Skeptical Science Comments

Comment on CO2 levels during the late Ordovician

dhogaza

gallopingcamel ...

L&C (2009) was quite thoroughly shot down in a follow-on paper in GRL.

And elsewhere ...

The best part of the story is how they cherry-picked snippets of data to fit their conclusion, though the bit about using model results that didn't include all changes in forcing to "disprove models" is a close second IMO (the model results they used had been generated to explore response to SST changes only). If they're going to complain that coupled atmosphere-ocean GCMs are giving incorrect results, one would expect them to actually *compare* with such results, wouldn't one?

James Annan was quick to pick up on that point.

I'm curious, is there any reason you read L&C (2009) in isolation? Or did you simply pick up a summary from one of the usual denial sites?

Comment on CO2 levels during the late Ordovician

Riccardo

gallopingcamel,
the often used aproximate relationship between forcing F and CO2 concentration is F(W/m^2)=5.35*ln(C/Co) and the temperature increase DT is proportional to the forcing DT=l*F where l is the climate sensitivity. So you get:

DT=5.35*l*ln(C/Co)

if you take Co as the current value (380 ppm) and a climate sensitivity of l=0.8 K/(W/m^2) you get different numbers.
Anyway, the linear aproximation between DT and F cannot be pushed as far as 10000 ppm.

Comment on CO2 levels during the late Ordovician

Ebel

The greenhouse effect has nothing to do with the heat conductivity - nothing to do with the change due to increase in CO2 concentration.

A saturation does not exist. Under saturation, some understand that on the surface of the earth emitted photons hardly reach the universe - but there is strongly absorbed which is also strongly emitted. Instead of reaching the ground than other photons emitted photons the universe - what does that have to do with saturation?

With increasing concentration of greenhouse gases is changing the pressure and temperature of the Earth's tropopause increasingly in the direction of Venus and Mars tropopause. The column pressure of CO2 in the Earth's tropopause is approximately 0.11 mbar - this is comparable to the pressures of the Venus and Mars tropopause, which are almost pure CO2 atmospheres.

Sincerely,

Comment on Watts Up With That's ignorance regarding Antarctic sea ice

doug_bostrom

GFW at 15:35 PM on 14 March, 2010

Yeah, the thing about curves is they don't have any notion of where to end. I do think that fitting curves to existing data is an interesting exercise, thought provoking, as long as one does not put on skis and follow the line wherever it leads, no matter how far.

Comment on CO2 levels during the late Ordovician

gallopingcamel

From Peru (#51), according to the IPCC (AR4) climate models the radiative forcing due to CO2 has a logarithmic relationship to global temperature. Thus using your numbers and taking today's conditions as a starting point the relationship between CO2 and global temperature should look like this:

1,000 ppm add 2.5 Celsius
2,000 ppm add 4.4 Celsius
10,000 ppm add 8.8 Celsius

While most scientists accept that CO2 has a significant effect some believe that the IPCC exaggerated the scale. For example, Lindzen & Choi (2009) suggest that the radiative forcing is six time weaker than the IPCC says. If L&C09 is correct you can divide the above temperature increases by a factor of 6.

The Venusian atmosphere is ~97% CO2 (970,000 ppm). If our atmosphere had the same composition one would expect temperatures to be ~21 Celsius higher than today assuming the IPCC is right.

Please note that I am a physicist rather than a climate scientist so the real experts may dispute my numbers!

Comment on Watts Up With That's ignorance regarding Antarctic sea ice

GFW

Hmm, I think Dr. Roper's heart is in the right place, but his curve fits are a little too theoretical and make unwarranted extrapolations. For example, he has this really cool fit to sea level as a function of temperature, but it ignores the fact that with the current configuration of the continents, it doesn't matter how hot it gets - 70 meters sea level rise is about all we can get by melting all the ice.

Comment on CO2 levels during the late Ordovician

GFW

I just realized one could misread my third sentence. Replace with "The temperature at a fixed altitude near the saturation threshold altitude goes up as the concentration of CO2 and the saturation threshold altitude both go up.

Comment on CO2 levels during the late Ordovician

GFW

The thing to understand about saturation is that there is always an altitude above which the absorption is not saturated. That altitude goes up with overall concentration of course. The temperature at that altitude goes up as the concentration goes up. But that means the temperature at every level below that altitude also goes up (search on "atmospheric lapse rate").

Comment on Guest post: scrutinising the 31,000 scientists in the OISM Petition Project

Philippe Chantreau

I'd go further and highlight thay any scientific field that is studied enough will, at some point, see the emergence of some level of consensus, unless no significant progress is being made in the understanding of that field. Scientific consensus is the normal extension of progressing knowledge.

Comment on CO2 levels during the late Ordovician

From Peru

If we continue to release CO2 to the atmosphere, at what point will the CO2-greenhouse effect saturate (that is, the point at which all the IR in the CO2-absorbed wavelenghts is absorbed, so that any further CO2 concentration increase will have no effect on greenhouse effect)?

1000 ppm?
2000 ppm?
10 000 ppm?

By the way, is Venus already CO2-saturated in the CO2 wavelenghts?

Comment on Guest post: scrutinising the 31,000 scientists in the OISM Petition Project

greendirectionconsulting

Phillippe Chantreau writes:
There seems to be some misunderstanding as to what scientific consensus means...The consensus model of Earth climate slowly emerged from all the research being done. Study after study being reviewed and published. It is not a consensus of opinion but of research results

Brilliant! - about time somebody highlighted this. The denialists represent the consensus that we talk about basically as meaning that we are saying that a majority of scientists believe a certain thing.

All they did with the Oregon petition was craft a cleverly weasel worded statement, as I pointed out earlier in these comments, that enabled them to say 'look - this huge number of "scientists" don't agree with the consensus' and Bob's your Uncle - an enduring denier meme, supremely and successfully misleading to the general public, was born.

Perhaps we need to emphasise that it is the enormous weight of evidence and research that is the "consensus" view.

Comment on Watts Up With That's ignorance regarding Antarctic sea ice

doug_bostrom

A fellow posted here yesterday with a curve fitting/function derivation exercise for Antarctic sea ice versus ozone hole intensity (sorry, not enough coffee yet, can a hole be "intense?").

Antarctic Summer Sea Ice Area

Prof. Roper surmises from his exercise that Antarctic sea ice should shortly be heading into decline, but he adds the caveat, "Many more data are needed in the future to make this date more certain."

Dr. Roper does some other fun derivations elsewhere on his site, mostly based on paleo data. Interesting to think about. He has a large collection of ruminations on global warming from a physicist's perspective here:

Global Warming Web Pages by L. David Roper

I hope Dr. Roper will continue to post here.

Comment on Watts Up With That's ignorance regarding Antarctic sea ice

Peter Hogarth

There was a question about how ice melts at -13 C, of course Johns figure 3 is temperature anomaly, with seasonal variations removed. If we put them back in:

The data is NOAA: http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries (-70 to -90 latitude loaded). These are monthly values so the summer daily values will be a bit higher judging by the Northern Hemisphere monthly/daily data. Anyway, the chart gives the idea, (temp in summer can get above freezing)...

90.BerÃ©nyi PÃ©ter at 11:18 AM on 11 March, 2010

Nice graphics! the 2002 minimal Ozone hole is curious, but there's bigger dips/peaks in sea ice elsewhere. Though there is good evidence of significant Antarctic sea ice reductions in the 20th century overall, the small upwards trend over past 30 years is the interesting factor.

Comment on Guest post: scrutinising the 31,000 scientists in the OISM Petition Project

Tom Dayton

Following up on Philippe's comment about the consensus being based on evidence rather than simple voting, here is a link to Naomi Oreskes's new talk, which addresses that topic right from the start. She even responds to skeptics who bring up Galileo as a counterpoint.

Other commenters have pointed to this talk repeatedly, but some other commenters seem to not have bothered to watch it. It would be more productive if some of the commenters who deny the role of consensus in science, were to react specifically to Oreskes's points.

Comment on CO2 levels during the late Ordovician

Peter Hogarth

One of the main points of this post is that our understanding of temperature and CO2 levels over the past few million years has evolved and become much more detailed over the past few years. As we look more closely at new higher resolution data we find that the linkage between temperature and CO2 is very tight, and it seems previous ideas about high temperatures concurrent with low CO2 levels were based on incorrect interpolations over huge geological time periods. We also find that some other higher estimates of ancient CO2 levels need to be revised. For example the 2010 paper by Breecker reports âAtmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100â. It appears that for paleosols, (fossil soils, one of the main proxy sources for estimating ancient CO2 levels) previously assumed soil CO2 concentrations during carbonate formation were far too high (by factors of around 2 or more). If this is taken into account it follows that ancient climates did not involve variations of 1,000s of ppmV of CO2, and past greenhouse climates were accompanied by concentrations similar to those currently projected for A.D. 2100. In addition the corrected paleosol record agrees more closely with other independent proxy paleo-evidence (such as that from fossil plant stomata) which adds confidence in both results. Obviously this gives some perspective on current rising levels of CO2 and temperature.

Breeckers work has been commented on by Dana Royer in 2010, Fossil soils constrain ancient climate sensitivity . Here she follows up on estimates of CO2 sensitivity up on her earlier work summarized graphically (2009) in Climate Sensitivity during the Phanerozoic: Lessons for the Future . This shows that recent revisions of climate sensitivity (change of temperature due to doubling of CO2) derived from paleo records have been converging on values around 3 degrees C.

Some have asked about CO2 rise preceding temperature rises in the past, and to add to what Ned at 02:18 AM on 13 March, 2010 has listed:

âThe Paleocene-Eocene Thermal Maximum (PETM) occurred approximately 55 million years ago, and is one of the most dramatic abrupt global warming events in the geological record. This warming was triggered by the sudden release of thousands of gigatons of carbon into the atmosphere and is widely perceived to be the best analogue for current anthropogenic climate changeâ This is quoted from Productivity feedback did not terminate the PETM Torfstein 2009. It has also been argued in Carbon dioxide forcing alone insufficient to explain PETM warming. (Zeebe 2009) that either current estimates of climate sensitivity are underestimates (as Breeckers work suggests), or that other positive feedbacks or causes are operating. In Ocean chemistry and atmospheric CO2 sensitivity to carbon perturbations throughout the Cenozoic (2010) Stuecker and Zeebe add that recent work indicates an increased sensitivity to carbon cycle perturbations and state âwe expect much more severe effects in the near future than during the PETM because of the likely higher anthropogenic release rate (even at the same total carbon input)â.
There is also earlier evidence (120 million years ago) of dramatic negative consequences of rapid increases in CO2 from MÃ©hay 2009, âA volcanic CO2 pulse triggered the Cretaceous Oceanic Anoxic Event 1a and a biocalcification crisisâ.

We must also appreciate (as John pointed out) that the gradual increase in solar output over the past 4 billion years (which we can estimate from looking at similar stars at various stages in their evolution) is likely to lower the threshold of CO2 levels at which the transition between glacial (we still have ice caps on Greenland and Antarctica, as well as the Himalayas) and essentially ice free conditions will occur, as well as other temperature sensitive thresholds or tipping points.

The link between glaciation (obviously related to temperature) and CO2 levels, and the effects of positive feedback, lags, etc are covered comprehensively in the scientific literature, but I list some recent work Flower 2009 ,
Langebroek 2009, (for middle Miocene, 13.9 million years ago)
Tripati 2009 (covering the past 20 million years), Westerhold 2009 âthe crossing of a critical pCO2 threshold may have led to the formation of the first ephemeral ice sheet on Antarctica as early as_50 Ma agoâ

None of this work precludes other drivers (lesser or greater) for global temperature and climate, and in geological history as well as now, other factors must be taken into account (such as insolation, plate tectonics, etc) but the weight of evidence for rising/falling CO2 levels being a significant cause as well as an effect of temperature rising/falling is overwhelming and increasing, and explanations for climate change which do not include CO2 have so far either been falsified or have been diminished in significance due to conflicting, ambivalent or updated evidence.

Comment on Guest post: scrutinising the 31,000 scientists in the OISM Petition Project

Philippe Chantreau

There seems to be some misunderstanding as to what scientific consensus means. Nobody has polled the members of scientific associations and ranked their opinions to come up with a consensus.

The consensus model of Earth climate slowly emerged from all the research being done. Study after study being reviewed and published. It is not a consensus of opinion but of research results. When considering these results as a big picture, a certain model can be defined, which is supported by an overwhelming preponderance of evidence, very much like in Ned's plate tectonics comparison.

Within that model, some stuff will be settled, some will have a certain level of uncertainy or unresolved inconsistencies, some will be the subject of much debate and some will even be unknown. This applies to Quantum Theory as well as Evolution or Climatology. None of it is "proven true." Science does not provide truth. Truth is vocabulary appropriate in the law, theology, politics and so forth.

In science, the word truth should be limited to the qualification of mathematical facts, really. Science attempts to understand reality. It does that by approximating with models, mind constructs. Since it is well known that these are approxiamtions, "truth" is out of the question.

Scientific consensus is in fact a strong statement of validity. It means that a very large body of research points in a certain direction, not that a number of people in positions of influence agree to make a model the "chief" model. There is no choice as to what the model is: it is dictated by the evidence.

There are numerous theories very much shakier than the consensus model of Earth climate. It would be very interesting to subject theories used in psychology, medicine, economics and many other fields to the same level of scrutiny applied to climate science and see how they hold up.

I would also be interested to see how the experts in these fields would react when faced with media campaigns aimed at having their expertise challenged by amateurs, their work and reputation attacked, and throwing each and every word they write or say into endless spins of misquote and misinterpretation.

Comment on CO2 levels during the late Ordovician

dhogaza

Current deforestration is causing soils to wash away and exposing large areas of fresh rocks in the tropics to the atmosphere. This increaes the rate of rock weathering and therefore c02 is also being removed from the air at greater rates due to current deforestation. Never heard this mentioned from pro AGW advocates.

Thingadonta ... as regards global warming per se, we don't need to understand the carbon cycle. We *measure* the rate of increase of CO2 directly, and we have quite solid figures on how much CO2 we spew into the atmosphere. The difference between the two tells us that carbon sinks take up about half of the CO2 we emit, and apparently that relationship's been quite constant for decades.

I'm not saying that people don't study the carbon cycle, it's a hot area of research, primarily because of interest in what happens in the future. Will sinks continue to absorb CO2 at the same rate? Faster? Slower? Plus just the general curiousity that science brings to the study of the world - we should know precisely how the carbon cycle works because it's our species' nature to try to understand questions of this sort.

So there's lots of work going on in the area under the umbrella of research related to climate change, and of course a lot is known, i.e. the amount of CO2 absorbed by the oceans, etc.

But it's just not terribly relevant to the broader discussion of CO2-forced global warming. CO2 goes up by a measured rate, sensitivity lies between 2.5-4C, so we can expect a range of warming in the future, the significance of which depends on the actual sensitivity. Narrowing the uncertainty of sensitivity is more crucial for policy then the understanding the full details of the carbon cycle, along with things like sea level rise and other impacts.

Comment on CO2 levels during the late Ordovician

Philippe Chantreau

We should probably keep in mind that there is only so far that climates can be compared between vastly different geological eras.

Our current glaciation/deglaciation cycles apply to continents and, more importantly, oceans as they are configured today.
http://www.whoi.edu/oceanus/viewArticle.do?id=2508

Under different conditions, especially different oceanic circulations, tresholds for climatic regime changes would likely be different.

So, really, what should preoccupy us is how different our current CO2 levels are from anything seen during the whole glaciation/deglaciation record of the past few hundred thousand years.

Comment on CO2 levels during the late Ordovician

chriscanaris

Thanks for pointing out the reference to the lower Ordovician insolation. I chased up the reference to the Royer 2006 paper - sorry but I haven't yet mastered the hyperlinks. However, it says:

âGlobal climate models calibrated to mid-Cenozoic conditions suggest a threshold of 560â1120 ppm (DeConto and Pollard, 2003; Pollard and DeConto, 2005), however during the Late Ordovician surface conditions were different, most notably in having an ~4% lower solar constant. A consequence of this decreased luminosity is that if all other thermal forcings were held constant, the CO2 threshold for initiating glaciations would be higher.â

I guess we are not that far away from 560 ppm, which could be a worry.

However, how does this 4% lower insolation compare with insolation as per the Maunder Minimum? The thread âWhat would happen if the sun fell to Maunder Minimum levels?â started on 19/02/10 argues inter alia for the very weak influence of solar forcing. The use of very different units - percentages as per Royer and Watts/M2 in the Maunder Minimum thread - makes it difficult to know how much weight to give the 4% insolation figure.

Comment on CO2 levels during the late Ordovician

John Mason

Should have added.... the pervasive leaching that led to the bleached wall-rocks clearly took a very long time indeed.... in post-glacial times the lead-bearing lodes have had ~12,000 years worth of weathering but with only modest results.