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Arctic sea ice melt - natural or man-made?

Posted on 9 June 2008 by John Cook

Arctic sea ice has declined steadily since the 1970s. However, the 2007 summer saw a dramatic drop in sea ice extent, smashing the previous record minimum set in 2005 by 20%. This has been widely cited as proof of global warming. However, a popular mantra by climatologists is not to read too much into short term fluctuations - climate change is more concerned with long term trends. So how much of Arctic melt is due to natural variability and how much was a result of global warming?

The long term trend in Arctic sea ice

Global warming affects Arctic sea ice in various ways. Warming air temperatures have been observed over the past 3 decades by drifting buoys and radiometer satellites (Rigor 2000, Comiso 2003). Downward longwave radiation has increased, as expected when air temperature, water vapor and cloudiness increases (Francis 2006). More ocean heat is being transported into Arctic waters (Shimada 2006).

As sea ice melts, positive feedbacks enhance the rate of sea ice loss. Positive ice-albedo feedback has become a dominant factor since the mid-to-late 1990s (Perovich 2007). Older perennial ice is thicker and more likely to survive the summer melt season. It reflects more sunlight and transmits less solar radiation to the ocean. Satellite measurements have found over the past 3 decades, the amount of perennial sea ice has been steadily declining (Nghiem 2007). Consequently, the mean thickness of ice over the Arctic Ocean has thinned from 2.6 meters in March 1987 to 2.0 meters in 2007 (Stroeve 2008).

 

Global warming has a clearly observed, long term effect on Arctic sea ice. In fact, although climate models predict that Arctic sea ice will decline in response to greenhouse gas increases, the current pace of retreat at the end of the melt season is exceeding the models’ forecasts by around a factor of 3 (Stroeve 2007).

 


Figure 1: September Arctic Sea Ice Extent (thin, light blue) with long term trend (thick, dark blue). Sea ice extent is defined as the surface area enclosed by the sea ice edge (where sea ice concentration falls below 15%).

What caused the dramatic ice loss in 2007?

The sudden drop in sea ice extent in 2007 exceeded most expectations. The summer sea ice extent was 40% below 1980's levels and 20% below the previous record minimum set in 2005. The major factor in the 2007 melt was anomalous weather conditions.

An anticyclonic pattern formed in early June 2007 over the central Arctic Ocean, persisting for 3 months (Gascard 2008). This was coupled with low pressures over central and western Siberia. Persistent southerly winds between the high and low pressure centers gave rise to warmer air temperatures north of Siberia that promoted melt. The wind also transported ice away from the Siberian coast.

In addition, skies under the anticyclone were predominantly clear. The reduced cloudiness meant more than usual sunlight reached the sea ice, fostering strong sea ice melt (Kay 2008).

Both the wind patterns and reduced cloudliness were anomalies but not unprecedented. Similar patterns occurred in 1987 and 1977. However, past occurances didn't have the same dramatic effect as in 2007. The reason for the severe ice loss in 2007 was because the ice pack had suffered two decades of thinning and area reduction, making the sea ice more vulnerable to current weather conditions (Nghiem 2007).

Conclusion

Recent discussion about ocean cycles have focused on how internal variability can slow down global warming. The 2007 Arctic melt is a sobering example of the impact when internal variability enhances the long term global warming trend.

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Comments 51 to 100 out of 529:

  1. chris "On the other hand, if a secular temperature showing large preindustrial variability is adopted, such as MOBERG05, the climate is found to be very sensitive to solar changes and a significant fraction of the global warming that occurred during last century should be solar induced. If ACRIM satellite composite is adopted the Sun might have further contributed to the recent global warming. From the Conclusion: Phenomenological reconstructions of the solar signature in the Northern Hemisphere surface temperature records since 1600 N. Scafetta1 and B. J. West2
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  2. chris "low frequency, internal radiative forcing amounting to little more than 1 W m-2, assumed to be proportional to a weighted average of the Southern Oscillation and Pacific Decadal Oscillation indices since 1900, produces ocean temperature behavior similar to that observed: warming from 1900 to 1940, then slight cooling through the 1970s, then resumed warming up to the present, as well as 70% of the observed centennial temperature trend. While the proposed mechanism is admittedly speculative, it is also speculative to alternatively assume that low frequency changes in the general circulation associated with ENSO and the PDO do not cause non-feedback TOA radiative budget changes on the order 1 W m-2 - an amount that is less than 1% of the mean radiant energy flows of 235 W m-2 in and out of the Earth’s climate system. Based upon the evidence, it seems likely that the neglect of sources of internal radiative forcing has resulted in diagnosed feedbacks which give the illusion of a climate system that is more sensitive than it really is. This has then led to the development of climate models which produce too much global warming in response to the external radiative forcing caused by anthropogenic greenhouse gas emissions." From Summary and Discussion: Internal Radiative Forcing And The Illusion Of A Sensitive Climate System Roy Spencer University of Alabama at Huntsville April 22, 2008
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  3. leebert, I don't disagree that your quotes by Ramanathan are probably accurate. However they are soundbites that tell only part of the story. Statements from press releases and press releases in general are not very good primary sources for the science. However we have the very recent review by Ramanathan and Carmichael at hand (see citation in my posts above), and you have given us the url to Ramanathan's prepared testamonial for the Wegman hearing. These give a very straightforward account of the science according to Ramanathan, and I recommend you read Ramanathan's Wegman hearing testimonial again carefully. i.e.: http://oversight.house.gov/documents/20071018110734.pdf Rather than soundbites, it (and the Ramanathan & Carmichael review) gives a considered scientific account. It's then straightforward to come away with unambiguous conclusions concerning Ramanathan's interpretation of his (and other's) data: These are: (i) If one is interested in the Earth's average surface temperature anomaly, which we all take to be the parameter by which global warming is assessed, atmospheric aerosols en masse (including black carbon, atmospheric brown clouds and sulphurous/nitrous aerosols and so on) result in nett cooling of the Earth's surface. (ii) This results from the fact that aerosols (especially black carbon) have the dual effect of both cooling the surface by reflecting or scattering incident solar irradiation, preventing some of it from reaching the Earth's surface - global "dimming", and the atmospheric warming effect of trapping or scattering incident solar irradiation or (especially black carbon), absorbing solar irradiation reflected from the Earth's surface. (iii) We can't talk about the atmospheric warming contributions of aerosols without also considering the cooling contributions, particularly since the latter dominate the total effect of aerosols. As Ramanathan says in the Wegman testimonial you urled (url copied above - see page 5), after describing that the nett anthropological aerosol effect is a cooling one of -1.5 Wm-2 (+/- a bit) while the net anthropogenic greenhouse forcing is equivalent to +3 Wm-2: "..it leads to the conclusion that, globally, ABCs may have masked as much as 50% (+/- 25%) of the warming due to greenhouse gases." (iv) and of course it logically follows that if one were to eliminate anthropogenic aerosols the world would warm. Ramanthan states this very clearly (page 5 again): "The logical deduction from this estimate is that, if and when air pollution regulation succeeds in eliminating emission of these particles, the surface warming can intensify by about 0.7 to 1.5 K, where the range is due to a range in assummed climate sensitivity of 2 to 4 K per doubling of CO2." I don't think I or Ramanathan could say this more clearly! The nett anthropogenic aerosol effect is to cool the Earth. (v) Now if we could remove black carbon selectively (not easy since BC emissions occur with other emissions, and much of the BC warming effect is due to its interactions with other aerosols), then we could get a nett "once and for all" cooling, and this could help mitigate the effects of continued anthropogenic release of greenhouse gases. This is because black carbon's atmospheric warming effect is larger (by around 0.9 Wm-2 averaged globally) than it's surface cooling effect. I won't address your points about politics/activism, since I think one needs to get the science right before addressing the latter...
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  4. re #50 - You're still not getting it Quietman. Tung and Camp's analysis relates to the damped variation of the Earth's surface temperature response to the solar cycle. Their analysis suggests that they can pull out a solar cycle variation of nearly 0.2 oC. That means for example that at the solar cycle maximum near 1991 to the solar cycle minumum near 1997, the solar contribution was a cooling one by around 0.18 oC (according to Tung and Camp....from 1997 minimum to the maximum near 2001 the solar contribution was to add back that warmth....from 2001 to 2007/8 the solar cycle contribution subtracted that 0.18 warmth again...and so on... in other words the Earth has a slow damped cyclic response to the solar cycle. No one expects otherwise. Tung and Camp's value (0.18 oC solar cycle max-min) is a bit larger than others find. But it makes no nett warming/cooling contribution (unless the strength of the solar cycle varies very significantly). So as the Earth's surface warms under the influence of enhanced greenhouse gas forcing, so the sun provides a small cyclic warming---cooling---warming----cooling----warming etc. (it's the solar cycle!). Right now the solar cycle is making a slight cooling contribution, but during the next few years its contribution is going to be adding to the anthropogenic greenhouse gas contribution..... You truncated the Conclusion section from Tung and camp's preprint. I've reproduced it below the dotted line at the bottom of the post. Notice that the second thing that Tung and Camp determine is a measure of the Earth's climate sensitivity to doubling of atmospheric CO2 (or CO2 equivalents). They determine a value of 2.3 - 4.1 K (oC) per doubling of atmospheric CO2 equivalents. This is pretty much exactly what the rest of the scientific measurements of the Earth's climate sensitivity to CO2. Tung and Camp are pretty much in accordance with the rest of the science on solar and greenhouse gas contributions to the Earth's temperature. ---------------------- Full conclusions from Tung and Camp's paper that Quietman partially reproduced in post #50 " Using NCEP reanalysis data that span four and a half solar cycles, we have obtained the spatial pattern over the globe which best separates the solar-max years from the solar-min years, and established that this coherent global pattern is statistically significant using a Monte-Carlo test. The pattern shows a global warming of the Earth’s surface of about 0.2 °K, with larger warming over the polar regions than over the tropics, and larger over continents than over the oceans. It is also established that the global warming of the surface is related to the 11-year solar cycle, in particular to its TSI, at over 95% confidence level. Since the solar-forcing variability has been measured by satellites, we therefore now know both the forcing and the response (assuming cause and effect). This information is then used to deduce the climate sensitivity. Since the equilibrium response should be larger than the periodic response measured, the periodic solar-cycle response measurements yields a lower bound on the equilibrium climate sensitivity that is equivalent to a global warming of 2.3 °K at doubled CO2. A 95% confidence interval is estimated to be 2.3-4.1 °K. This range is established independent of models."
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  5. Re #51 and #52 It's unfortunate, Quietman, that you feel the need to hijack this thread by dumping inappropriate stuff. I just don't see the point. We've already seen that Tung and Camp is pretty much a mainstream paper, the conclusions of which are in accordance with solar/climate science in general (their max-min solar cycle contribution is a bit larger than others get, but their climate sensitivity measure is smack in the IPCC range). Let's very briefly (since this isn't the thread to address this stuff) look at the others. Spencer's paper. It seems odd that you've dumped both Spencer's paper and Tung and Camp's paper at the same time. They're totally incompatible. Spencer is pretending that some unsupported phenomenon ("internal radiative forcing") means that the Earth doesn't respond to enhanced greenhouse gas forcing as pukka science indicates. However Tung and Camp's analysis indicates that the Earth warms at equilibrium by 2.3 - 4.1 oC per doubling of atmospheric CO2. That's exactly what the rest of informed mainstream science says too. So which is it Quietman? You need to come to some conclusion yourself before just dumping inappropriate papers here. Scaffeta and West's paper is a mathematical exercise that addresses the issue entirely phenomenologically according to a set of "what if..." assumptions. They are neither climate nor solar scientists and their paper is a hypothetical exercise. Scientists that do solar science have established that the sun hasn't made any significant contribution to the warming of the last 30-odd years. Here's the Director for the Sun-Heliosphere Department of the Max Planck Institute for Solar System Research, Sami Solanki, writing in a paper several months ago [***]: ["The observed correlations between the Sun's behaviour and the Earth's climate have completely failed since the 1970s. In the past 30 or 40 years the Earth's temperature has gone up much more rapidly than you would expect from the Sun – indeed there is strong evidence that since 1985 all the changes in the Sun have been in the opposite direction to that required to warm the Earth."] and: ["But, in our view, there is no doubt at all that the ongoing global warming is not being caused by the Sun but mainly by the greenhouse gases such as CO2 that we are emitting."] [red]***[/red][i][b]Priest, Lockwood, Solanki and Wolfendale (2007)[/i] Astronomy & Geophysics Volume 48 Issue 3 Page 3.07-3.07.[/b]
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  6. Quietman:"I do read the papers, but I do not read into them, just the facts, not conclusions based upon some faith in a root cause." It seems that you don't read them that well, since you missed the entire conclusion of the T&C paper. Or when you say conclusions, do you mean the conclusions of the authors themselves? Furthermore, you put together papers whose conclusions are totally incompatible, and you do so only because they appear to support your opinion on one point, while in fact they don't really do that, which you would know if you actually read the papers. Leebert, you accuse activists of sweeping the issue of soot under the rug. Yet a relatively recent Gristmill article does a fairly accurate rendition of what Ramanathan found out, and it seems to agree with your position on the necessity of targeting BC. I did not read your (very)extensive post there - not as much disposable time as you or Chris - but I noticed that it was there for all to read, i.e. nobody tried to sweep it anywhere. Grist is as greenly active as it gets. A quick glance at what Greenpeace has on its site indicated that they would be highly favorable to any kind of reduction in BC soot emissions (surprise). I found little evidence on these "activist" sites that the issue was being avoided out of fear to detract from the CO2 problem. There may be a case to be made that it does not attract as much attention. Since the total particulate forcing is still negative (per Ramanathan), that lack of attention might not be as terrible a thing as you argue. According to yourself, it is rather governments that are trying to sweep the soot (highly inefficient way to dispose of it). You cited China and India but ironically, a little reading on the "activist" pages shows that the Bush EPA too has been trying its darndest to not enforce the CAA against industries violating particulate matter rules. Of course, they have been heavily criticized for that by, hmm, the activists. So you say that activists are trying to sweep the soot while they actually are actively fighting it. You also say that polluting countries governments are trying to sweep the soot, and in the case of the US they are doing so against opposition from the activists. Confusion indeed. As for the Ramanathan paper, there is anything but confusion in Chris's mind. His review is outstanding and does a much better job of carrying the author's findings than the press release you cited. FYI, I am not an "activist" and I'm interested in all the science about these issues that is accessible to me. Big thanks to Chris, who just made a bunch of science more accessible and also summarized it and nicely emphasized some important points (gee, you should get paid for that!). And finally, Leebert, I totally agree with you that BC emissions should be selectively reduced by all possible means.
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  7. The Grist article and Leebert's post: http://www.grist.org/news/2008/03/24/soot/index.html That post does look interesting a first glance. A Greenpeace account of "field work" or whatever you'd want to call it: http://www.projectthinice.org/blog/view/13057/ Snippet: "We are also seeing a lot of dark material (soot) covering some of the flatter ice as well. Anywhere there is soot, the snow is melting away faster than the surrounding areas." Would the Greenpeace people (green activists if there ever were some) really publish that kind of stuff if they wanted to sweep it under the rug?
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  8. Philippe, Chris, Thanks for the info. I too am short on time these days so I can't cover all the bases. Perhaps the crux of the misunderstanding is this: The brown clouds may provide a net masking but the BC detracts from the total possible masking. Is that a better synopsis? (FWIW I never intended to conflate BC with all global aerosol clouds). And when Ramanathan states that 40% of the Pacific's temp. anomalies are being caused by BC, I find that a very clear statement. Yes, it's a one-time fix, but it's also a 20-year window. Philippe: I'm glad to see GreenPeace along with Grist have come along but big environmental newspaper writers like Andy Revkin (dot Earth) have actively pooh-poohed the entire question of soot deposition in the Arctic. Good grief, I practically handed it on a plate to Revkin. He blew it off, discounting it as marginal against other dynamics affecting ice. John Tierney took interest, however. And if the activists *KNOW* about the airborne soot issue, then why aren't they announcing it as part of their campaign? Is their message getting diluted by the media? For the politicos to raise heck about polar bears & the Arctic w/out talking about soot mitigation seems disingenuous. There's something wrong with the game plan, and having been involved in a couple of activist organizations, I come into this with some pretty strong suspicions about their politics (having endured rants by 9/11 Truthers and anti-capitalists, etc.). Science fat vs. activist fancy? Well.... The climate moderates who suspect CO2's global impact tending toward the lower bounds are happy to pursue soot & ozone mitigation first and as objective efforts they seem far more feasible and certain. I think a gradual, stepped conversion to a low-carbon society is entirely feasible, but getting per capita CO2 output down to preindustrial levels by 2050? Not bloody likely! There's more to be learned, however, about aerosols in general. One of the big hangups the honest skeptics have about dangerous CO2-driven warming is that the temperature anomalies are lower in the southern hemisphere where BC is far less common (as are all aerosol levels). This, as opposed to the Arctic's 25 perc. of sesquicentennial AGW, largely due to sootfall (around 80-90%). I think a great many misgivings about climate science would be relieved if these apparent NH vs. SH discrepancies could be addressed. Is it b/c of the relative lack of BC coupled with a function of the Antarctic or ENSO? NCAR's Ken Ternberth's recent apostasy re: the Argo floats has kept the discussion very much alive, as have the recent studies showing lower relative humidity in the middle troposphere and less water vapor in the Antarctic as well. How those all shake out will take some time, as will Keenlyside. The calls against complacency don't seem to address the temperature plateau, since even were more warming due, the relative plateau (relative to the 1990's) doesn't seem to portend a worst-case outcome. Without the anticipated pipeline of heat in the seas, and with every year of slowed warming relative to accelerated CO2 levels, nature would have to exhibit an exponential rate of warming relative to CO2 levels alone. That seems truly unlikely to me. The climate stance of Pielke, Carter, Spencer, Lindzen, etc., is seeming more reasonable, that other mitigating factors are at play (cloud dynamics). If the honest skeptics are mistaken, what could be misleading them? Net aerosol effects? Help me then: The sun has dimmed -0.1 degrC worth since the early 1990's, that's about a -0.07/decade offset (and it's due to dim more) while the low end of aerosol masking -0.09 degr/decade, sea temperatures are currently stable (last I checked). If temperatures rise despite those negative forcings, there's a big problem. If temperatures remain stable with those negative forcings intact, will be fair to surmise those would represent the CO2 signal? That'd be a 0.18 degr/decade signal. Not ideal, but is it dangerous? People like good hard numbers, but not sound bites that scream "panic." Those breed suspicion b/c it smells like demagoguery. Smart people can read a balance sheet that accounts for the sun's dimming, the real net aerosol maskings, the Arctic warming (and what of it can be reversed), etc. Those IPCC bar graph & summaries are inadequate to the task. W/out some clearer figures as to what society is really dealing with the majority of people are going to be understandably reluctant to embark on a big program. What I constantly read looks like some very incomplete science and lots of politics. If you wonder why people resist the theory of dangerous AGW, this is why. What the CO2 mitigation program looks like is a self-administered austerity program (barring a sudden expansion of low-carbon technologies). Austerity programs hurt, and hurt big, and can even impair the ability to pay for a conversion to a low-carbon society. W/out a lot of extra heat in the pipeline, do we really need to pursue something so drastic, then? Already Britain is verging on an anti-green rebellion, the invasive burden of gov't interference would cause a real revolution here in the 'states. Japan says they can't afford Kyoto-level targets. The EU is looking at losing their steel industry to Asian steel makers. And with increasing trade deficits it's hard to bear yet more economic burdens. Bjorn Lomborg is correct in pointing out that we can't afford everything (even w/out big SUVs), so we can only do what's feasible. Which... brings us back to soot.
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  9. Just a brief piece of info to inform this discussion, "As we approach the time of year of the peak of areal coverage of Arctic sea ice and the minimum areal coverage in Antarctic sea ice, Climate Science is presenting a status report based on the excellent data analysis provided at the University of Illinois website The Cryosphere Today. The coverage for January 31 2008 is about 900,000 square kilometers below average for the Arctic [Northern Hemisphere] (see) and about 500,000 square kilometers above average for the Antarctic [Southern Hemisphere] (see). The Illinois website has also introduced an effective display of past Arctic sea ice coverage at the same time of the year (see Compare Daily Sea Ice)." http://climatesci.org/2008/01/31/current-status-of-arctic-and-antarctic-sea-ice-coverage/ Now, I really don't know what's causing the difference btw Arctic and Antarctic sea ice, but there certainly seems to be a large non-C02 component to sea ice variation. Cheers, :)
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  10. chris Re: "I just don't see the point." I agree.
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  11. Philippe Chantreau "conclusion" is the heading to the section for the quote (cut and paste, nothing added). I stopped arguing my point when I realized the problem was a predetermined view of any paper referenced and an accusation of my not reading them. I take the authors for what they say, no inference. In once case the author actually states three possibilities, that is what words like "IF" usually mean. This I consider a credible argument, the author says "IF" rather than making an assumption that a hypothesis he did not propose is a fact. The other paper clearly states that AGW needs a rethink, not that the hypothesis is bad but that it isn't good either. Again, given the evidence, this is credible. To blandly argue that a hypothesis is true because your friends say so is totally without merit.
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  12. phillipe I only have one point to make - nature has much greater effect on climate than AGW. All of the papers that I use for reference support this stance if you read them carefully without presupposition. I am an environmentalist but moreover I am a naturalist in the traditional sense of the word. I live in accord with nature. I study it for what it is and do not believe in tampering with it in any way for any reason. But I can read, have been for a very long time, first course in how climate works was those science books for children back in the 50s. I do not appreciate good work being twisted to meet someones agenda. I have read your comments in all of these posts and while I don't always agree with your views I do respect them.
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  13. chris On "Rhodes Fairbridge and the idea that the solar system regulates the Earth's climate." August 24th, 2007 by Warwick Hughes. "Rhodes is one of the few scientists to research the sun/climate relationship in terms of the totality of the sun’s impact on the earth (i.e. gravity, the electromagnetic force and output and their interaction)." ... "Rhodes also researched the idea that the planets might have a role in producing the sun’s variable activity. If they do and if the sun’s variable activity regulates climate, then ultimately the planets may regulate it." As for Dr. Mackey, the scientist you tore apart, his views are contained in his replies in a blog: Richard Mackey says: December 28th, 2007 at 5:03 am I suggest if you disagree with him that you contact him yourself. Richard Mackey. The article published by Dr. Fairbridge can be found here.. I am sorry but I do not have access the the published paper that the article is based on, nor his later papers. But the article is quite clear and in plain english. Dr. Fairbridge and his hypothesis is also referenced in this recent paper: Fingerprints of a Local Supernova by Oliver Manuel and Hilton Ratcliffe, which explains implications of the hypothesis.
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  14. chris Sorry - in my last post I meant to link Mackey's email address, epitrochoid@hotmail.com, but linked his office by mistake.
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  15. Quietman:"conclusion" is the heading to the section for the quote (cut and paste, nothing added)." Nothing added, but some omitted, see the complete conclusion given by Chris in post 54. Do you dispute that Tung and Camp come up in that paper with a sensitivity of 2.3 K at CO2 doubling? You talk about twisting good work. Tung and Camp reach a value for climate sensitivity to CO2 doubling that is almost identical to what the IPCC says, yet you suggest that their paper demonstrates that the climate sensitivity to CO2 has been overestimated by mainstream climate science (of which we'll assume IPCC's reports to be representative). I don't understand.
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  16. leebert/shawnet (#58/#59): You both mention the difference in effects in the Northern and Southern hemisphere in general (leebert) and specifically in relation to sea ice extent (Shawnet). You suggest that this is a problem for climate science, leebert: e.g. post #58 you say: [“One of the big hangups the honest skeptics have about dangerous CO2-driven warming is that the temperature anomalies are lower in the southern hemisphere where BC is far less common (as are all aerosol levels). This, as opposed to the Arctic's 25 perc. of sesquicentennial AGW, largely due to sootfall (around 80-90%). I think a great many misgivings about climate science would be relieved if these apparent NH vs. SH discrepancies could be addressed. Is it b/c of the relative lack of BC coupled with a function of the Antarctic or ENSO? “] But these discrepancies have been addressed at length, and this is a rather well understood phenomenon relating to the heat capacity of the oceans (more ocean in the S. hemisphere and thus greater heat capacity there) and ocean circulation properties (much more efficient transfer of surface heat in the deep Southern oceans compared to the Arctic oceans). The possibility that black carbon might play a role is possible. However remember that man-made atmospheric aerosols have a cooling effect overall (see Ramanathan’s work discussed at length on this thread), and since these are produced and concentrated largely in the Northern hemisphere, that seems a less than likely interpretation, unless, of course one is dealing only with the effects of ice-deposited black carbon. Here’s some excerpts from a recent review of ocean circulation modelling in which the mechanisms for hemispheric warming asymmetry are described, and illustrating that highly delayed Antarctic Circumpolar ocean warming has been predicted since the early 1980’s. One of the problems of this, of course, is that while the high latitude Southern oceans are apparently taking up much of the surface heat by transfer to the deeper layers, at some point this will become inefficient, and thus one might expect the Southern hemisphere warming to kick in… Here’s a bit of a summary from (direct excerpts are in [“bracketed quotation”] marks): S. Manabe and R. J. Stouffer (2007) Role of Ocean in Global Warming; J. Meterolog. Soc. Jpn. 85B 385-403. General point about ocean modulation of surface warming: [“In response to the increase in greenhouse gas in the atmosphere, the positive temperature anomaly initially appears in the well-mixed surface layer of the ocean called the “mixed layer”. Gradually, the anomaly spreads from the mixed-layer to the deeper layers of the ocean, thereby increasing the effective heat capacity of the oceans. The increase of effective heat capacity, in turn, results in the reduction of the rate of increase in surface temperature, reducing and delaying the warming as shown by Hoffert et al (1980) and Hansen et al. (1984).”] Discussing the early models of Schneider and Thompson (1981) to evaluate the delay in the response of the sea surface temperature to gradual increase in CO2, Manabe and Stouffer say: [“Their study shows that the time-dependent response of zonal mean surface temperature differs significantly from its equilibrium response particularly in those latitude belts, where the fraction of ocean-covered area is relatively large. Based upon the study, they conjectured that the response in the Southern Hemisphere should be delayed as compared to that in the Northern Hemisphere because of the inter-hemisphere difference in the fraction of the area covered by the oceans.”] In a later model Bryan et al (1988) made the same sort of analysis, investigating the role of the oceans in modulating the response of surface warming to enhanced greenhouse gases. [“They found that the increase in surface temperature is very small in the Circumpolar Ocean of the Southern Hemisphere in contrast to high latitudes of the Northern Hemisphere where the increase is relatively large.”] It’s not just the oceans per so of course. It’s also ocean and air currents, and particularly the mechanisms governing the efficiency of surface heat transfer into the deeper oceans. If this is efficient, the deep oceans will absorb heat and there might be little measured surface warming, at least for a while. So (speaking of Bryan et al (1988)) again: [“However, the detailed analysis of the numerical experiment reveals that the absence of substantial surface warming in the Circumpolar Ocean is attributable not only to the large fraction of the area covered by the oceans but also to the deep penetration of positive temperature anomaly into the oceans.”] Later models predict the same hemispherical Asymmetry that is seen in the real world. e.g. discussing the simulations of Manabe et al (1992): [“Figure 3 also reveals that there is a large asymmetry in surface warming between the two hemispheres. In the Northern Hemisphere, the surface warming increases with increasing latitude, and is particularly large in the Arctic Ocean. This is in sharp contrast to the Southern Hemisphere, where warming is relatively large in low latitudes and decreases with increasing latitudes. It becomes small in the Circumpolar Ocean of the Southern Hemisphere, particularly in the immediate vicinity of Antarctic Continent.”] Why is this, one might ask?! Here’s what Manabe and Stouffer say: [“One can ask: why the polar amplification of warming does not occur in the Southern Hemisphere, despite the existence of extensive sea ice which has a positive albedo feedback? As discussed in the following section, the absence of significant warming in the Circumpolar Ocean of the Southern hemisphere is attributable mainly to the large thermal inertia of the ocean, which results from very effective mixing between the surface layer and the deeper layers of ocean in this region. This is in sharp contrast to the Arctic Ocean, where very stable layer of halocline prevents mixing between the surface layer and the deeper layer of the ocean.”] [“In view of the absence of significant surface warming, it is not surprising that the area coverage of sea ice hardly changes in the Circumpolar Ocean despite the CO2-doubling.”] (n.b. remember this is a prediction from a model; we’re nowhere near CO2 doubling yet!). However that's what we're seeing in the real world. and so on….
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  17. Philippe The portion I point out in the conclusion is what is overlooked most often. I left out the obvious because long posts, like long reports, are normally not read. I have written many papers in my field and know that the summary and conclusion are what most people read, and not intently. In the blog Climate Science linked to in 63, Richard Mackey and Leif Svalgaard discuss this same paper. The conclusion is the opinion the authors have arrived at from their study. The body of the paper gives the facts used to arrive at that conclusion. But it is better to read the entire paper to determine the facts.
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  18. Just a brief point here, chris. "But these discrepancies have been addressed at length, and this is a rather well understood phenomenon relating to the heat capacity of the oceans (more ocean in the S. hemisphere and thus greater heat capacity there) and ocean circulation properties (much more efficient transfer of surface heat in the deep Southern oceans compared to the Arctic oceans). The possibility that black carbon might play a role is possible. However remember that man-made atmospheric aerosols have a cooling effect overall (see Ramanathan’s work discussed at length on this thread), and since these are produced and concentrated largely in the Northern hemisphere, that seems a less than likely interpretation, unless, of course one is dealing only with the effects of ice-deposited black carbon." The efficiency of heat transfer would be a good explanation for why the changes SH ice are of different magnitude than those of the NH IMO, but is not a particularily good explanation of why the sign of those changes is different. If the difference in ice buildup was primarily governed by the efficiency of heat transfer at the poles, one would expect the sign of the changes to be the same(one would just be slower than the other). Quietman, thanks for the link to the Rhodes Fairbridge article. Interesting stuff. Cheers, :)
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  19. shawnet, Yes, fair enough. I think the overall conclusion might be that the Antarctic sea ice is overall stable right now, whereas that in the Arctic is receding rather rapidly. If one considers the rate of change of Antarctic sea ice in the period late 1987 to now, this is a very small trend of around +12,000 km2 per year. During the same period, the Arctic sea ice trend is around -85,000 km2 per year (the trend from the start of 2001 is of the order of -131,000 km2 per year in the Arctic). One can see that the Antarctic sea ice isn't really doing a huge amount: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.south.jpg (cf the arctic sea ice: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg ) and although direct satellite measures of sea ice are only available since the mid-70's, the less direct data indicate that Antarctic sea ice extent was larger in the period 1900-1960 than now[***], so perhaps the Antarctic sea ice is just undergoing a bit of a small fluctuation/recovery. As expected, global surface warming just isn't penetrating wholesale into the Southern polar regions as it is in the Arctic. The Antarctic is a very big place 'though, and as we know some parts are undergoing some significant warming, especially the Antarctic peninsula and the Pine Island Bay region of West Antarctica, and this seems actually to be resulting in overall mass loss of the Antarctic ice sheet [*****]. But no-one considers significant loss of the Antarctic polar ice to be very likely, whereas the loss of Arctic sea ice and attenuation of some of the Greenland ice sheet is a real concern for the future... [***] N. A. Rayner et al. (2003) Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century; Journal Of Geophysical Research, 108, NO. D14, 4407. [*****] H. D. Pritchard & D. G. Vaughan (2007) Widespread acceleration of tidewater glaciers on the Antarctic peninsula, Journal Of Geophysical Research, Vol. 112, F03S29 E. Rignot et al. (2008) Recent Antarctic ice mass loss from radar interferometry and regional climate modelling, Nature Geoscience 1, 106 – 110.
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  20. Philippe In that last sentence please note "equivalent to a global warming of 2.3 °K at doubled CO2." You and chris have not been paying very close attention to the wording. The paper does not support chris' view, which is why Mackey used it to support his view in the Climate Science blog that I linked above in #63.
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  21. Re #70: You need to explain clearly what you are trying to convey there Quietman. Otherwise your comment is an unsubstantiated and cryptic one! Here's what Tung and Camp conclude and how this compares with other independent analyses as compiled, for example, in the IPCC reports. Tell us where you disagree with this interpretation and why: (i) Tung and Camp calculate a measure of the Earth's climate sensitivity to radiative forcing equivalent to an equilibrium temperature rise of 2.3 - 4.1 oC per doubling of atmospheric CO2 at 95% confidence levels. (ii) The IPCC climate sensitivity determined from an analysis of many studies, is an equilibrium temperature rise of 1.5 - 4.5 oC per doubling of atmospheric CO2 at 95% confidence levels. (iii) In other words Tung and Camp are in accord with the results of a whole slew of independent analyses compiled by the IPCC that indicates that the Earth's surface temperture responds to a forcing eqiivalent to a doubling of atmospheric CO2 somewhere near 3 oC (+/- a bit at 95% confidence levels.
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  22. Quietman, you also mentioned Spencer and his "internal radiative forcing." This is, by Spencer's own admission, a speculative mechanism. Put in your words, it would be a "root cause" in which one must have "faith." That's only part of the problem with it. As all other scientific works, it is open to scrutiny, some of which can be found here: http://www.realclimate.org/index.php/archives/2008/05/how-to-cook-a-graph-in-three-easy-lessons/langswitch_lang/sp#more-567 That same thread mentions how Spencer and Christy also have a history of allowing for years the use of data that had been shown to be invalid. I'm highly skeptical about Spencer's work, with much better reason than him saying stuff different from my "friends." In any case, that paper is very much incompatible with Tung and Camp, and it would invalidate their work if proved correct.
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  23. Philippe Acknowledged. I am skeptical about any hypothesis until it has been proven. But it does have some merit. I lean towards the Fairbridge idea because it is the most logical. Green activists don't like it because it's not about AGW, but it does explain why there is more vulcanism and tectonic activity in recent years and is not incompatible with Tung and Camp's paper. PS The friends remark was not aimed at you so please do not be offended. It was aimed at closed minds that will not even look at a paper if they don't like the author.
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  24. Philippe Solar-Cycle Warming at the Earth's Surface and an Observational Determination of Climate Sensitivity. By Ka-Kit Tung and Charles D. Camp From the Abstract: This model-independent, observationally-obtained climate sensitivity is equivalent to a global double-CO2 warming of 2.3 -4.1 °K at equilibrium, at 95% confidence level. The problem of solar-cycle response is interesting in its own right, for it is one of the rare natural global phenomena that have not yet been successfully explained. From the introduction: On the other hand there is a recurrent warming of the earth by the solar cycle. The periodic nature of the phenomenon allows the use of more sophisticated signal processing methods to establish the reality of the signal. Since the forcing is known, contrasting solar-max and solar-min years over multiple periods yields a pattern of earth’s forced response, which is better than previous attempts of using “warm-year analogs in recent century”--- some of which may be due to unforced variability --- to infer information relevant to future CO2 forcing. Our procedure for the solar-cycle signal yields an interesting pattern of warming over the globe. It may be suggestive of some common fast feedback mechanisms that amplify the initial radiative forcing. Currently no GCM has succeeded in simulating a solar-cycle response of the observed amplitude near the surface. Clearly a correct simulation of a global-scale warming on decadal time scale is needed before predictions into the future on multi-decadal scale can be accepted with confidence.
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  25. Philippe My remark about reading comprehension earlier refers to little oversights like the one below: "During the last 20 years or so, there has been a reversal from dimming to brightening at stations worldwide (Power, 2003; Wild et al., 2005)." C. W. Stjern, J. E. Kristjánsson, and A. W. Hansen, 2008 (link given in #17 above) Which says the exact opposite of what chris said.
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  26. re #75: That's a tad dishonest Quietman. Here's what chris said! (see post #12): referring the steady attenuation of arctic sea ice since the 1960's: ["ii) "solar brightening from lack of aerosols". Nope. The atmospheric aerosol load has increased rather significantly since the 1960's. Thus enhanced Arctic sea ice melt has increased despite the overall decreased solar irradiation reaching the surface. Rather than "solar brightening" we've actually had a bit of "solar dimming"."] This is consistent with the paper that you cited (Stjern et al (2008); urled below[***], in which solar irradiation reaching the surface is averaged over 11 high Northern latitude stations as an indication of "dimming"/"brightening". The relevant data is summarized in their Figure 3 which shows that from the 1960's (the period from which Arctic sea ice retreat began) the total surface irradiation in the high Northern latitudes has decreased very significantly (i.e. nett "dimming"), and therefore this is unlikely to be a causal factor in the long term decrease of Arctic sea ice since the middle of the last century. More specifically, the "surface solar irradiation" averages around 115 W/m2 in 1960 (note that fewer stations were monitored during this period) and decreases progressively to reach a low near 103 W/m2 around 1987 from which it recovers a bit to reach a level near 106/107 W/m2 now, still well below the levels of the early 1960's. http://folk.uio.no/jegill/papers/Stjern_etal_2008_IJClim.pdf
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  27. Re #74 Quietman Why not explain as clearly as you can, how you interpret Tung and Camp’s manuscript, with respect to their analysis of climate sensitivity. I did so in post #71. However you’re pursuing this argument by innuendo and allusion, and it’s not easy to know what you are trying to convey (at least in a scientific sense). When I have time I’ll post a more detailed explanation of my interpretation (it seems a very straightforward manuscript to me). Then we can see where the problem of interpretation lies.
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  28. Refocussing on the subject of this thread (the attenuation of Arctic sea ice) and the specific question of solar "dimming"/"brightening" in the Arctic and its potential contribution to sea ice recession, there are several relevant studies [e.g. *; **; ***] and these seem to yield a generally consistent conclusion. The Arctic sea ice has steadily receded since the 1960's although the trend has quickened (faster attenuation of summer sea ice) since around 2001. http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seasonal.extent.1900-2007.jpg During this period the solar irradiance measured at the surface has decreased at least through the mid 1980's (measured in high latitude Northern European stations [*]) and through the mid 1990's measured in Arctic stations [**], [***] (i.e. "solar dimming"). During the last decade or perhaps a bit longer it has recovered somewhat (less "solar dimming" or "solar brightening"!). However the solar irradiance at the surface is still a good bit lower now than it was in the 1960's (in other words the recovery from "solar dimming" has been smallish) [*]. What does this mean? (i) It's unlikely that variations in solar surface irradiation measured at the surface can have made a contribution to Arctic sea ice attenuation during the period since the 1960's since the variation has been in the wrong direction ("dimming"). More likely the "solar dimming" has mitigated somewhat the contributions (enhanced sea and surface temperatures; albedo effect including black carbon!) at least up 'til the mid-1990's. (ii) It's possible that the quicker pace of sea ice recession since around 2000, has a contribution from the small reduction in "solar dimming" since the mid-1990's. In other words the aerosol effects that were likely countering sea ice recession in the 1960's-1980's, are now doing so less effectively. [*] C. W. Stjern et al (2008) Global dimming and global brightening - an analysis of surface radiation and cloud cover data in northern Europe; submitted to Int. J. Climatol. http://folk.uio.no/jegill/papers/Stjern_etal_2008_IJClim.pdf [**]S. T. Weston et al (2007) Interannual solar and net radiation trends in the Canadian Arctic Journal Of Geophysical Research 112, D10105 [***] Stanhill G (1995) Solar Irradiance, Air-Pollution And Temperature-Changes In The Arctic, Philosophical Transactions Of The Royal Society Of London Series A- 352 247-258 ------------------------------------------ abstracts/extracts: [**] Although the trends are not explicitly linear, both data from Alert and Resolute Bay show an overall decrease in K↓ over the past half-century. Data from Alert shows a decrease of 2.25% of the daily mean CI, and Resolute Bay shows a decrease of 2.50% of the daily mean CI per decade. Although further data are needed to tell conclusively, it also appears that both sites show a recent recovery over the past decade. As is speculated by other authors [e.g., Stanhill, 1995; Lohmann et al., 2004; Che et al., 2005], it is most likely that changes in atmospheric constituents (aerosols and/or greenhouse gases) are the major cause. Further study in this area is definitely warranted. (K↓ is solar radiation; CI is daily "clearness index") [***] A highly significant decrease in the annual sums of global irradiance reaching the surface of the Arctic, averaging 0.36 W m(-2) per year, was derived from an analysis of 389 complete years of measurement, beginning in 1950, at 22 pyranometer stations within the Arctic Circle. The smaller data base of radiation balance measurements available showed a much smaller and statistically non-significant change. Reductions in global irradiance were most frequent in the early spring months and in the western sectors of the Arctic, coinciding with the seasonal and spatial distribution of the incursions of polluted air which give rise to the Arctic Haze.
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  29. chris at 01:33 AM on 19 June 2008 (#76) "re #75: That's a tad dishonest Quietman" Re: (ii) "solar brightening from lack of aerosols". Nope. The atmospheric aerosol load has increased rather significantly since the 1960's. Thus enhanced Arctic sea ice melt has increased despite the overall decreased solar irradiation reaching the surface. Rather than "solar brightening" we've actually had a bit of "solar dimming". This is consistent with the paper that you cited (Stjern et al (2008); urled below[***], in which solar irradiation reaching the surface is averaged over 11 high Northern latitude stations as an indication of "dimming"/"brightening". IN Global dimming and global brightening - an analysis of surface radiation and cloud cover data in northern Europe BY Camilla W. Stjern1,2 , Jón Egill Kristjánsson1 and Aksel Walløe Hansen3 IT CLEARLY STATES IN QUITE PLAIN ENGLISH THE FOLLOWING: "In the more recent decades, most of our stations show a turn to brightening, which agrees with the new global trend described by Wild et al.(2005)." "While Stanhill (1995) reported of widespread dimming in the Arctic up to the mid-1990s, the present study shows a turn to brightening also here." We are not talking about 1995 - this is about an event in summer 2007. That is what I mean when I say something is dated. Things have changed in the last few years. "Using NCEP reanalysis data that span four and a half solar cycles, we have obtained the spatial pattern over the globe which best separates the solar-max years from the solar-min years, and established that this coherent global pattern is statistically significant using a Monte-Carlo test. The pattern shows a global warming of the Earth’s surface of about 0.2 °K, with larger warming over the polar regions than over the tropics, and larger over continents than over the oceans. It is also established that the global warming of the surface is related to the 11-year solar cycle, in particular to its TSI, at over 95% confidence level." From the Conclusion: Solar-Cycle Warming at the Earth’s Surface and an Observational Determination of Climate Sensitivity. By Ka-Kit Tung and Charles D. Camp This is compared (equated) EQUIVALENT TO CO2 MODELING - NOT CAUSED BY CO2. THIS ALSO IS PLAIN ENGLISH. You can not expect someone to reply to arguments based on interpretations of papers that only support their own view rather than the authors conclusions.
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  30. I have been telling people for years that there is a huge difference between natural warming and Human related warming. One big problem with most Environmental scientists is that they apparently have never studied other sciences, and for the most part know which side of the warming "bread" holds the butter. By which I mean that there is little or no research money for scientists who don't toe the Warming line. Take polar ice melting for example. I can name some people who are quite glad, even if they don't know it, that the poles are melting. The people of the state of Texas. Remember Glaciers once covered most of what we now call North America. These glaciers have been receeding for thousands of years. We human types have only been measuring these changes for a few hundred years at best and tend to think that the Earth is a static place. It is not static. Here is a great example of what I mean. According to www.glacierbay.org when George Vancouver first sailed into Icy Strait in 1794 Glacier Bay was but a dent in a "Grand Pacific Glacier" some 4000 feet thick in places and some 20 miles wide. By 1879 when John Muir explored the bay the glacier had receeded some 30 miles, all without the help of humans, their cars and coal fired power plants. Lets face it the poles have been melting for a long time. Does that mean we should continue to burn fossil fuels at today's alarming rate? Hell no. Even if those fuels didn't pollute the Earth it would make best sense to use solar, wind and other renewable sources. Will we end up like Venus or Mars? Hell no. Venus is just too close to the sun and Mars lost it's atmosphere because it's core cooled and the magnetic field that protects a planet's atmosphere was lost. Are we destroying the Earth? Again no. We may not be able to live here anymore, but the Earth will be just fine.
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  31. (i) Quietman, science has its basis in straightforward presentation of data and honest discussion of that data and its interpretations. Skepticism is not about using semantic confusion and misrepresentation to attempt to make things appear other than they are [In this case your assertion that Stjern et al (1980) and my comments are not consistent!]. And one should read papers carefully and look at the data presented. It would be a wonderful piece of work that didn’t contain one or two sentences that, taken in isolation, could be construed to mean something that wasn’t quite consistent with the data and interpretation presented. But one shouldn’t hunt out these sentences/phrases, and attempt to construct an “argument” on them! See paragraph (iii) below. (ii) The bottom line is that (as John Cook outlines clearly in his top article, as does Kay et al, 2008, and so on), the evidence indicates that the anomalous arctic sea ice melt last summer is a consequence of a long term (30-40 years) persistent attenuation of arctic sea ice due to global warming and albedo feedbacks, on which a hardly-anomalous “weather” occurrence acted on an already-denuded and thinned ice sheet. (iii) Since the total solar irradiance measured at the surface has diminished during this long period according to the manuscript that you highlighted [down from 115 W/m2 around 1960, to a low near 103 W/m2 in the late 1980’s to a partial recovery to around 106/7 W/m2 now – see Figure 3 of Stjern et al (2008)], one can conclude that the nett contribution of aerosols in the arctic during the long period of attenuation of sea ice since the 1960’s has been a cooling one. In other words aerosols have protected the arctic sea ice from the full effects of enhanced-greenhouse-induced warming. The paper that leebert brought to our attention (Ramanathan and Carmichael; e.g. see posts #39, #48), makes a similar conclusion for the total aerosol contribution on a worldwide basis, which of course indirectly affects the arctic since it’s the transfer of excess thermal energy to the high northern latitudes that is a major contributor to the marked warming there. Might the apparent reduction in the aerosol effect in the arctic in the last 10 years have contributed to the more rapid attenuation of sea ice since the turn of the century? Yes of course (see post #78). However the aerosol “dimming” effect is (according to Stjern et al, 2008) still larger than in the 1960’s. In any case a reduction of “dimming” is not something we take much comfort from. As Ramanathan and Carmichael point out, clearing the skies of our aerosols will have the effect of further enhancing the warming resulting from our large enhancement of the earth’s greenhouse effect. And of course the aerosol effect, whether it’s increasing or decreasing, is another man-made contribution to the earth’s energy “budget”. That’s clear again I hope. I've repeatedly reiterated my meaning (in posts #19, #76, #78, and now here)..I'm not sure I can say it more clearly!
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  32. Quietman, Tung and Camp are pretty clear about their meaning in relation to climate sensitivity. You've done what you did with the Stjern paper, and are constructing you’re entire “argument” around extraordinary selective précis based on selective quoting. That’s not science and it ain’t skepticism either! Notice that the bit you’ve just reproduced (in your post #79) from Tung and Camp’s conclusion leaves out completely the second element of Tung and Camp’s analysis which is to use their analysis to calculate a value for the climate sensitivity. Let’s look carefully at Tung and Camp. (here’s the url:) http://www.amath.washington.edu/research/articles/Tung/journals/solar-jgr.pdf We are concerned here with what Tung and Camp mean when they refer to the “climate sensitivity” and whether this calculated “climate sensitivity” is in accord with the large number of independent studies that have been compiled by the IPCC to yield a “climate sensitivity”, which in standard usage, refers to the Earth’s equilibrium temperature response to a doubling of atmospheric [CO2]. Since doubling of atmospheric CO2 results in an enhanced radiative forcing of around 3.7 W/m2, one could also express the “climate sensitivity” in terms of the Earth’s equilibrium warming response to an enhanced radiative forcing of 3.7 W/m2. The mainstream scientific data compiled by the IPCC indicates that the Earth’s “climate sensitivity” is equivalent to a warming of 3 oC, plus/minus a bit at 95% confidence of warming due to doubled atmospheric [CO2]. Explicitly the 96% confidence range is 1.5-4.5 oC of warming per doubling of atmospheric [CO2] – this is the “climate sensitivity”. Tung and Camp’s manuscript (urled above) is numbered line by line throughout, so we can indicate clearly to what we are referring. Note that at this point we’re not interested in whether Tung and Camp is wrong or right - we’re taking their paper and its analysis at face value, and trying to make a clear interpretation of what they mean: (i) Clearly Tung and Camp’s measure of climate sensitivity is very similar to that of other mainstream science. It’s near 3 oC plus/minus a bit at 95% confidence level. The range is a bit tighter that that complied by the IPCC. That’s obvious from what they say in reference to their calculated climate sensitivity (see lines 16-18 in the abstract): [“This model-independent, observationally-obtained climate sensitivity is equivalent to a global double-CO2 warming of 2.3 -4.1 °K at equilibrium, at 95% confidence level.”] (ii) Do Tung and Camp mean by “climate sensitivity” what everyone else means by “climate sensitivity”. In other words are they referring to the forcing resulting from a doubling of atmospheric [CO2]? Yes. In lines 32/33 they say (referring to their estimate of the forcing from the solar cycle minimum to the maximum) : [“This solar radiative forcing is about 1/20 that for doubling CO2 (δQ~3.7 Wm-2).”] So they are in accord with the straightforward analysis that doubling [CO2] yields a radiative forcing of 3.7 W/m2 (iii) Do Tung and Camp agree that the IPCC complied data yields a 95% confidence range of “climate sensitivity” of 1.4 – 4.5 oC per doubling of atmospheric [CO2]? Yes. In lines 46-49, they say: [“Confidence in these models would be greatly increased if their climate sensitivity---currently with a factor of three uncertainty, yielding 1.5 °K to 4.5 °K equilibrium warming (ΔT2xCO2) due to a doubling of CO2 in the atmosphere [Houghton and et al., 2001]---can be calibrated against nature’s.”] (iv) Does the climate sensitivity calculated by Tung and Camp refer to the equilibrium warming resulting from a radiative forcing from doubling atmospheric [CO2]? Yes. In lines 51-55, they indicate that their method of determining the climate sensitivity will allow information about future CO2 forcing: [“Since the forcing is known, contrasting solar-max and solar-min years over multiple periods yields a pattern of earth’s forced response, which is better than previous attempts of using “warm-year analogs in recent century”--- some of which may be due to unforced variability --- to infer information relevant to future CO2 forcing.”] (see vi) and (vii) too! (v) Do Tung and Camp think that their “best value” of the climate sensitivity is nearer 2.3 oC rather than 3 oC? No. Tung and Camp’s value of 2.3 oC per doubling of atmospheric [CO2] (or per radiative forcing of 3.7 W/m2) is a lower bound: lines 373-377: [“Fortunately, a period of 11years is long enough to yield a useful lower bound. We can combine our lower bound, obtained completely independent of models, with the upper bound obtained also in a model-independent way by Forster and Gregory [2006] (subject to the assumption of priors mentioned above) to yield the following 95% confidence interval:”] and: lines 382-383: [“The lower bound of 2.3 °K happens to be the same as the model-derived value (2.4 °K) of Murphy et al [2004] after converting it into the 5-95% range of the latter; it is ~1 °K higher than the previous IPCC lower bound.”] and Tung and Camp explicitly state that they consider that the climate sensitivity is near 3 oC lines 364-366: [“Nevertheless, since the observed time lag in the solar-cycle response is small (see Appendix), our best guess is that the equilibrium climate sensitivity should not be too different from 3.0 °K.”] (vi) are Tung and Camp really talking about a climate sensitivity that is equivalent to the earth’s equilibrium surface warming due to a doubling of atmospheric [CO2}? Yes. The entire discussion leading up to their determination of climate sensitivity is done within the framework of previous determinations of values for the climate sensitivity, which is the Earth’s surface temperature warming at equilibrium in response to doubling atmospheric [CO2] (see lines 287-355) (vii) are we absolutely sure?! Yes. Tung and Camp express their climate sensitivity value explicitly in terms of a temperature range encompassing the 95% confidence levels that result from a doubling of atmospheric [CO2]: See their equation 2 (line 379) in which their climate sensitivity value is expressed as its range at 95% confidence: 2.3 °K< ΔT2xCO2 <4.1 °K . (“2xCO2” is subscripted) This can be stated verbally as: “2.3 degrees Kelvin is less than the change in temperature from doubling [CO2], which is less than 4.1 degrees Kelvin” And they’ve already assured us [see point (iii) above] that “deltaT2xCO2” means “equilibrium warming due to a doubling of CO2 in the atmosphere”.
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  33. Just spitballing here, but mightn't a possible explanation be that the cooling aerosols affect temperature generally (ie all the air) whereas soot has a highly concentrated effect. A particle of soot lying on an ice sheet will heat up directly on that ice sheet and will only affect the air temperature after that heat radiates out. Thus, soot could have a small overall heating(air temperature) affect and a large *melting* effect. Cheers, :)
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  34. shawnet, It's a reasonable possibility for a contribution....particles of soot lying on the ice might have a significant effect. You can see a similar effect walking in the mountains in the spring...where snow has melted back enough that rocks are poking out of the snow, there's usually a clear melt zone (like an empty "moat") around each rock, due to the absorbance of solar heat by the rock and the radiation of that warmth to the surrounding snow. According to one of the scientists that leebert referred to, and work published in Science last year [*], that might have had a significant effect in the arctic. However, according to a detailed analysis of black carbon found directly in Greenland ice cores [*], the largest deposition of "soot" (black carbon) was in the early to mid 20th century. The estimated early summer surface forcing was ~ 0.42 W/m2 before 1850, 1.13 W/m2 in 1850-1951 (and as high as 3.2 Wm2 in the early 20th century). It’s been around 0.59 W/m2 since 1951 to present. So at least by that analysis, soot on arctic ice (at least to the extent that Greenland ice cores are relevant) may not be having much more of an effect now than it was before 1850, although it may well have contributed to the attenuation of sea ice in the early part of the 20th century, when there was quite a sharp rise in arctic temperatures too... [*] J. R. McConnell et al (2007) 20th-century industrial black carbon emissions altered arctic climate forcing; Science 317, 1381-1384.
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  35. Here's an alternative POV, "Fig. 6 shows the change in surface albedo in our transient climate simulation for 1880–2002 for March to April and May to June. The specified spectral-mean snow albedo changes were 0.83 × 1.5% ~ 1.25% for snow/ice in the Arctic Ocean and 0.83 × 3% ~ 2.5% for snow over Northern Hemisphere land. The surface albedo changes are diminished over land by vegetation masking of the snow (14), which is very effective in forested areas but ineffective in tundra regions with little vegetation. The warming of the surface and air due to the soot albedo effect enhances the surface albedo changes over both land and ocean because of enhanced snow aging (increased grain size) and especially because of the earlier onset of spring melt. Thus, the soot-lowered albedo and increased temperatures initiate positive feedbacks via earlier snowmelt and rainfall. Fig. 5 shows the change in the net short-wave heating of the surface for the same periods as in Fig. 6. Note that the regional flux changes at the surface are as much as 10 W/m2 and more. This compares with a typical annual-mean forcing of <1 W/m2 (Fig. 1). Clarke and Noone (2) calculated a maximum May-to-June surface flux perturbation of ≈6 W/m2 for an assumed snow albedo perturbation of 2%. Given that our soot-imposed albedo change for the period 1880-2002 was only ≈1.25% (over sea ice), this means that we find a surface heating about twice as large as that calculated by Clarke and Noone (2). The cause of this difference is the positive feedbacks in our climate model that reduce the albedo further, especially the acceleration of the summer melt season. Our results are not in disagreement with those of Clarke and Noone (2), because they mentioned in their concluding remarks the likelihood that such positive feedbacks would enhance the soot albedo effect. These positive feedbacks, especially the acceleration of the melt season, have practical implications. The perturbations of surface fluxes are largest in the regions of sea ice, permafrost, glaciers, and the low altitude portion of the Greenland ice sheet that is subject to summer melt. This suggests that soot may contribute to thinning of sea ice (16), melting permafrost, glacier retreat, and accelerating movement of Greenland ice (17)." http://www.pnas.org/cgi/content/full/2237157100/DC1/2 Soot climate forcing via snow and ice albedos James Hansen * , and Larissa Nazarenko * Cheers, :)
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  36. Yes, fair enough...notice however that Hansen and Nazarenko: (i) conclude their abstract with ["However, soot contributions to climate change do not alter the conclusion that anthropogenic greenhouse gases have been the main cause of recent global warming and will be the predominant climate forcing in the future"] and: (ii) have, in their more recent work downgraded the role of black carbon/snow/ice albedo effects. The paper you cited is here: J. Hansen and L. Nazarenko (2004) Soot climate forcing via snow and ice albedos; Proc. Natl. Acad. Sci 101 423-428 (abstract below [*]) The paper can be downloaded from NASA/GISS: http://pubs.giss.nasa.gov/docs/2004/2004_Hansen_Nazarenko.pdf Note that Hansen and Nazarenko assign a total black ice/albedo forcing of 0.15 W/m2 and a total contribution to global warming since 1880 of 0.17 oC. However they later reassess this and downgrade the contribution of black ice/albedo forcing to 0.05 W/m2 (and total contribution to global warming of 0.065 oC) in their more recent study: Hansen, J. et al (2007) Climate simulations for 1880-2003 with GISS modelE. Clim. Dynam., 29, 661-696. (see Appendix A5) This can also be downloaded from NASA/GISS: http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_3_small.pdf A recent study by Flanner et al (2007), concludes that the BC effect in the arctic has been quite significant too [**]. Hansen and Nazarenko point out that the BC emissions that affect the arctic (mostly from Eurasia) dropped sharply in the 1990's due to the breakup of the former Soviet Union. So, again, that tends to argue against the contribution from BC as a major contributor to the acceleration of artic sea ice recession since around 2000, let alone the very dramatic anomalous drop of summer sea ice last year. Presumably the reduction in total aerosol load from Eurasia will have both "cooling" effects (reduction of BC component) and "warming" effects (reduction of aerosol screening of surface solar irradiation), so things are unlikely to be straightforward! e.g. Hansen and Nazarenko (2004) say: ["Snow samples in the 1980s (6), including sites in Alaska, Canada, Greenland, Sweden, and Spitzbergen, and on sea ice in the central Arctic, yielded typical BC amounts of 10–50 ppbw (excluding Greenland). "Arctic haze" studies (19) showed that most of the aerosols originated in Europe and the Former Soviet Union (FSU) in winter/spring driven by circulation around the Icelandic Low and Siberian High. BC emissions from Eurasia probably declined sharply in the 1990s as, e.g., FSU BC emissions fell by a factor of four with the collapse of the FSU economy (20). Reduced BC emissions are not necessarily permanent in the face of possible economic recovery, increased shipping in the opening Northwest and Northeast Passages, regional hydrocarbon resource development, and increased use of diesel-powered vehicles."] Hansen and Nazarenko (2004) abstract [*] "Plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of +0.3 W/m2 in the Northern Hemisphere. The "efficacy" of this forcing is 2, i.e., for a given forcing it is twice as effective as CO2 in altering global surface air temperature. This indirect soot forcing may have contributed to global warming of the past century, including the trend toward early springs in the Northern Hemisphere, thinning Arctic sea ice, and melting land ice and permafrost. If, as we suggest, melting ice and sea level rise define the level of dangerous anthropogenic interference with the climate system, then reducing soot emissions, thus restoring snow albedos to pristine high values, would have the double benefit of reducing global warming and raising the global temperature level at which dangerous anthropogenic interference occurs. However, soot contributions to climate change do not alter the conclusion that anthropogenic greenhouse gases have been the main cause of recent global warming and will be the predominant climate forcing in the future." [**]M. G. Flanner et al (2007) Present-day climate forcing and response from black carbon in snow, J. Geophys. Res. 112, D11202
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  37. John I think we are finding a little more evidence of my vulcanism hypothesis: "International expedition discovers gigantic volcanic eruption in the Arctic Ocean" Please read Fire under the ice Public release date: 25-Jun-2008, (natural causes).
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  38. Are you suggesting that the 1999-2001 events melted the ice in 2007?
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  39. Chris, "Hansen and Nazarenko point out that the BC emissions that affect the arctic (mostly from Eurasia) dropped sharply in the 1990's due to the breakup of the former Soviet Union. So, again, that tends to argue against the contribution from BC as a major contributor to the acceleration of artic sea ice recession since around 2000, let alone the very dramatic anomalous drop of summer sea ice last year. Presumably the reduction in total aerosol load from Eurasia will have both "cooling" effects (reduction of BC component) and "warming" effects (reduction of aerosol screening of surface solar irradiation), so things are unlikely to be straightforward!" I agree that BC is unlikely to be a major contributor in the last year. This is likely the result of a natural confluence of factors, especially considering that the sea ice extent has already rebounded to around the 2001-2002 levels.(http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg). Much more interesting IMO is why the Antarctic and Arctic changes are in opposite directions for the last while. BC may go part of the way to explaining this though it probably can't explain the whole thing. I wouldn't be surprised if the trend is the result of many things, possibly including ocean currents, BC and vulcanism. Cheers, :)
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  40. Shawnet, There are two questions aren't there! (a) What's caused the remorseless attenuation of arctic sea ice since the 1960's? (b) What's caused the massive excess summer melt in 2007? and you also asked again: (c) why the difference betwen the Nrthn. and Srthn. hemisphere? Question (b) has been more or less answered (see the excellent summary of the science by John Cook at the top of the page). It seems that the remorseless attenuation of arctic sea ice since the 1960's has made the ice sheet very vulnerable to short term summer "weather" conditions. Note that while the winter arctic sea ice extent has recovered a tad, it's the summer sea-ice extent that is the critical factor, and so we'll have to wait to see to what extent 2007 was a recoverable blip. Question (c) has been answered pretty much (see posts #66/#69) The differences in the effects of global warming on Antarctic and Arctic are reasonably well defined. It's largely a question of sea and ocean currents and the way that excess heat is distributed from the lower latitudes to the higher. There may be some BC contribution. After all there is little BC found in the Antarctic (on the other hand the cooling aerosols also predominate in the Arctic cf the Antarctic). Vulcanism is a red herring I suspect [for (a), (b) and (c)]. It doesn't make a lot of sense at all. One needs to make a clear cut explanation of how this "vulcanism" works. At the very least one needs to address the facts that: (i) the most volcanically-active region in the the Arctic or Antarctic is the area in and around Iceland (an eruption every 5 years on average; 1/3'd of all lava expelled in the last 500 years is in Iceland which not only sits astride the opening of the plates running along the opening Atlantic basin, but also above a "mantle plume")... ...however the region around Iceland and S. Greenland is the one area of the Arctic that has actually cooled a tad since the 1960's. How can "vulcanism" be an explanation for marked warming when the most volcanically-active region has cooled??? (ii) The vulcanism in the Arctic (and Antarctic) is of long-long-standing (millions of years). Without some evidence that this vulcanism has (a) all of a sudden increased markedly in the relevant regions and periods, (b) that any thermal energy is of a magnitude and appropriately distributed to contribute to the observed melt, and so on....one should remain rather skeptical of such a notion. Question (a) has an explanation that is well-supported by the scientific evidence: massive enhancement of the Earth's greenhouse effect. The warming in the arctic is pretty much as expected from supplementing the Earth's greenhouse gases with extra CO2, methane, nitrous oxides, tropospheric ozone and CFC's. There may well be a significant contribution from BC although we've had pretty much all the forcing from that source already according to Hansen and Nazarenko, and it's not clear that the warming effect of BC has been greater than the cooling effect of other manmade aerosols. Certainly according to Hansen, and Ramanathan and Carmichael, the total worldwide aerosol effect (BC et al) is a cooling one. It may be net warming in the arctic 'though. One would have to look at the numbers carefully, if the appropriate one's are available.
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  41. Philippe No more than AGW did, neither is about 2007. Both are about recent warming. I have seen evidence cropping up everywhere for increased worldwide vulcanism since 1976 but it has been steadily ignored. Am I the only one making the solar connection? Gravitational stress stronh enough to effect the sun has to also be more than strong enough to effect the earth's inner circulation.
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  42. Shawnet, the ice area is actually very close to what it was last year, due to a period of fast melting in the spring: http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png Quietman, you say " have seen evidence cropping up everywhere for increased worldwide vulcanism since 1976." Can you point to papers where that evidence is compiled and (better) analyzed?
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  43. Re "vulcanism" This notion seems to be creeping in, in an unsubstantiated manner! So it's worth pointing out that volcanic eruptions generally result in short periods of cooling due to the release into the high atmosphere of volcanic aerosols that are relatively quickly washed out of the skies. This is an obvious and well-documented effect of volcanos. Thus the eruption of Pinatubo and the subsequent trosposphere and ocean surface cooling "pulse" was useful in analysing the response of the Earth to reduced forcing and the rate of recovery after superficial cooling, and so on: e.g.: Soden BJ et al (2002) Global cooling after the eruption of Mount Pinatubo: A test of climate feedback by water vapor, Science 296, 727-730. And very large volcanic eruptions are well known for their rather unpleasant cooling effects (e.g. Tambora and the subsequent "year without a summer"). We've had quite a few volcanic eruptions since the middle of the last century, and so the global temperature rise has been periodically "knocked back" by these cooling "pulses": e.g. see Figure 1 of: http://pubs.giss.nasa.gov/docs/2005/2005_Hansen_etal_1.pdf So if someone has a notion that "vulcanism" is contributing to global (or regional) warming, then a little bit of substantiation with some scientific evidence would be nice!
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  44. chris "This notion seems to be creeping in, in an unsubstantiated manner!" It is unsubstantiated only to a few deniers. At all the other columns and blogs I have read, it is acknowledged. The world around you sees the increased vulcanism, why don't you? Or are you confusing vulcanism with eruptions? And don't bother to quote Hansen, he has too much to lose by admitting that he started this whole thing in error, rendering his work useless.
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  45. Undersea vulcanism - more than just eruptions and those eruptions do not cause cooling, they cause warming. This is not atmospheric ejecta. You have done your CO2 homework, not study up on vulcanism and plate tectonics, geomagnetism and ocean forcings.
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  46. Philippe Yes I could but there are too many. I did my homework, now you can google it just as easily. I have better things to do at this time of year. The weather is quite pleasant, low 70's with a cool canadian breeze and I have several acres to take care of. I have to restrict my on-line time to coffee breaks so I really do not have the time to look up the links for my paper collection which is a few hundred megabytes at this time. You and chris can continue believing in the CO2 induced AGW myth if you want to, otherwise investigate like I did.
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  47. Quietman, If you consider that "undersea vulcanism" is contributing to global (or regional) warming, then you need to give us some evidence. Remember that: (i) the mid-ocean plates have been slowly ripping themselves apart for countless (almost!) millenia. Has this process suddenly intensified since the middle of the 20th century? Evidence please. (ii) one of the more active mid ocean plate-separations lies towards and then in Iceland, as the plates carrying America and Europe rip apart at the mid-Atlantic ridge. This is a region with massive "vulcanism" (undersea and above sea). However, this region is one of the rare locations on earth that has actually cooled since the middle of the 20th century. How can "vulcanism" provide an explanation for warming (global or regional) if one of, if not the most active, region "vulcanism"-wise has actually cooled a tad since the mid 20th century? Explanation please. (iii) Science progresses on the basis of evidence. If you'd like to pursue "vulcanism" as a contributory factor in local or global warming, you'll need to find some evidence. You can't keep ducking these straightforward requests and expect to be taken seriously. Evidence please. Otherwise we're likely to be skeptical of your unsupported claims! Note btw: (a) that greenhouse-gas induced warming (resulting largely from massive enhancement of the atmospheric carbon dioxide concentration) is hardly a "myth". One of the very papers that you cited in support of something or other, concludes with a determination of the earth's climate sensitivity to doubling atmospheric [CO2]: 2.3 °K< ΔT2xCO2 <4.1 °K . (“2xCO2” is subscripted)[***] Which say's: “2.3 degrees Kelvin is less than the change in temperature from doubling [CO2], which is less than 4.1 degrees Kelvin” (Tung and Camp consider that the climate sensitivty is around 3 oC (+/- a bit). [***]Tung and Camp: http://www.amath.washington.edu/research/articles/Tung/journals/solar-jgr.pdf Clearly Tung and Camp don't consider man-made enhancement of the earth's greenhouse effect via massive enhancement of the atmospheric CO2 concentration "a myth". (b)that science doesn't progress on the basis of "blogs" and "columns"! (c) that unsubstantiated denigration of scientists (your unsubstantiated comments re Hansen) doesn't constitute skepticism! I hope you're not one of those " ...closed minds that will not even look at a paper if they don't like the author". (d) It's not only science that is all about the evidence. Skepticism too is all about the evidence!
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  48. Chris, "Question (a) has an explanation that is well-supported by the scientific evidence: massive enhancement of the Earth's greenhouse effect. The warming in the arctic is pretty much as expected from supplementing the Earth's greenhouse gases with extra CO2, methane, nitrous oxides, tropospheric ozone and CFC's. There may well be a significant contribution from BC although we've had pretty much all the forcing from that source already according to Hansen and Nazarenko, and it's not clear that the warming effect of BC has been greater than the cooling effect of other manmade aerosols. Certainly according to Hansen, and Ramanathan and Carmichael, the total worldwide aerosol effect (BC et al) is a cooling one. It may be net warming in the arctic 'though. One would have to look at the numbers carefully, if the appropriate one's are available." Chris, the point about the SH and NH is that the GE can't explain the loss of ice in the SH, *because there isn't one*. There's a gain(and one reasonably close to the loss in the NH). Since there is the same amount of CO2 in the SH as the NH, CO2 cant explain the state of the cryosphere in toto. Phillippe:"Shawnet, the ice area is actually very close to what it was last year, due to a period of fast melting in the spring: http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png" I don't think that what I said and what you said really disagree. It is just a question of what you are comparing it to. I was comparing it to the early part of this century, while your link compares it to the 1979-2000 mean. Cheers, :)
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  49. Quietman, thank you for the condescending tone. It is a good reminder of what we all should try to avoid, I will be more watchful to not reproduce anything like it. Shawnet, the comparison I was concerned about on that graph was between this year and last year. The current extent does not bode well for what Sep minimum will be, but time will tell.
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  50. Shawnet, the Tale of the Tape at Cryosphere Today seems to disagree with you: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg The magnifying function helps to see that the current level is significantly lower than any in 01-02. What data are you using?
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