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Weather vs Climate

Posted on 26 March 2011 by dansat

The "skeptic" claim "scientists can't even predict the weather right" is based more on an appeal to emotion than fact.  The inference is that climate predictions, decades into the future, cannot be possibly right when the weather forecast for the next day has some uncertainty.

In spite of the claim in this myth, short term weather forecasts are highly accurate and have improved dramatically over the last three decades. However, slight errors in initial conditions make a forecast beyond two weeks nearly impossible.   

Atmospheric science students are taught "weather is what you get and climate is the weather you expect". This is why this common skeptical argument doesn't hold water. Climate models are not predicting day to day weather systems. Instead, they are predicting climate averages. 

A change in temperature of 7 degrees Celsius (°C) from one day to the next is barely worth noting when you are discussing weather. Seven degrees, however, make a dramatic difference when talking about climate. When the Earth's average temperature was 7ºC cooler than the present, ice sheets a mile thick were on top of Manhattan! 

A good analogy of the difference between weather and climate is to consider a swimming pool. Imagine that the pool is being slowly filled. If someone dives in there will be waves.  The waves are weather, and the average water level is the climate. A diver jumping into the pool the next day will create more waves, but the water level (aka the climate) will be higher as more water flows into the pool. 

In the atmosphere the water hose is increasing greenhouse gases. They will cause the climate to warm but we will still have changing weather (waves).  Climate scientists use models to forecast the average water level in the pool, not the waves. A good basic explanation of climate models is available in Climate Change–A Multidisciplinary Approach by William Burroughs. 

Source: AMS Policy Statement on Weather Analysis and Forecasting. Bull. Amer Met. Soc.,79,2161-2163

*Image source: Meehl, G. A., C. Tebaldi, G. Walton, D. Easterling, and L. McDaniel (2009), Relative increase of record high maximum temperatures compared to record low minimum temperatures in the U.S.Geophys. Res. Lett.36, L23701, doi:10.1029/2009GL040736.

NOTE: This post is also the Basic rebuttal to "scientists can't even predict the weather right"

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Comments 101 to 131 out of 131:

  1. Umm, as to evidence that ENSO doesnt impact long term energy budget, then I would say total OHC from argo, from here, supported by sealevel rise. I also usefulness of models which I am sure you don't. Add in paleo estimates of climate sensitivity and I would say a very long way from "no evidence".
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  2. You point to 5 years of Argo data as evidence that ENSO wont change in the future and become biased one way or the other?

    You point to paleo estimates that show considerable natural variability and somehow reason that ENSO or other ntural effects like clouds didn't play a part?

    You're right about the models though. I dont have any doubt in my mind whatsoever with regards their usefulness for modelling altered future climatic conditions given their reliance on carfully tuned parameters that work against today's conditions.
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  3. My point was not evidence that ENSO won't change. It was evidence that ENSO is not much of a player in total OHC.

    I argue against ENSO because its very hard to see physical reason for it to be able to do so. Paleo estimates show uncertainty about sensitivity, which is not the same as variability. However, it is extremely difficult to account for past climate with sensitivity as low as you are trying to claim. Your turn, where is your evidence for low sensitivity. There is plenty of evidence for a number about 3.

    See model reliability thread for "careful tuning of parameters". Try some evidence to support that accusation. Show me where a model parameter was tuned to fit overall climate instead of the empirical data on which it was based, but post it over there, not here.
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  4. Tim 101,

    The warm water volume plotted there is only limited to a narrow band along the equator, according to the discharge oscillator theory the warm water discharges out of the region, and it doesn't mean that the overall OHC will change.

    scaddenp 102,
    From fig 2, I can see that there is a dip around 1997-1998, but then around 2008 there is a dip too, but that is a la nina year. Also from 2002-2005 there is an El Nino, but the mean looks flat there.
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  5. @IanC : NOAA was quite specific about their understanding of ENSO and OHC.

    ""El Niño/Southern Oscillation (ENSO) variability is intimately linked to alternating stages of oceanic heat content build-up and discharge in the equatorial Pacific (Wyrtki, 1985; Cane et al, 1986; Zebiak, 1989). "

    Hence if ENSO biases one way or the other in the future we can expect a related change in trend for OHC.
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  6. Tim, I saw your exchange with Gavin. I understood your comments about "where's the modelled results for OHC post 2003" to imply that Gavin knew what they were and was deliberately not publishing them because he thought they would be embarrassing. You obviously did not accept the response he gave you. It appears that moderator thought similarly. If this was not what you implied, then I fear you have expressed yourself badly.

    IanC, I stand corrected, I should have examined the data more closely before expressing an opinion where I know so little.
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  7. TimTheToolMan @108

    "variability is intimately linked to alternating stages of oceanic heat content build-up and discharge in the equatorial Pacific" The surface layer of the equatorial Pacific isn't the entire volume of the ocean. And if heat is being exchanged between the ocean and atmosphere this doesn't necesarily mean a change to Total Heat Content.

    That said anything that causes a heat flux into/out of the atmosphere is likely to have implications for atmospheric phenomena that impact on the heat balance to space. So a more permanent ENSO switch could possible cause a change to THC, a set point change if you will. But I can't see how this could lead to a longer term change in OHC TREND!
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  8. scaddenp

    Fig 2 from Lyman is interesting. Looks like a plateau in the mid 90's, a rise then another plateau in the late 2000's. Could that be the solar cycle?

    Obviously dangerous to read too much into eyeballing short range graphs.
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  9. Tim 108,

    That statement is made in the context of the discharge oscillator model, where heat is transported in and out of the equatorial region horizontally. The build up is due to heat outside the equatorial strip transported into the strip, so if you add up the heat content from region where WWV is calculated, and the heat content of the ocean outside the region there should be no change.

    P.3 of Meinen and McPhaden 2010 contains a diagram that explains the discharge oscillator theory. The svendrup transport is a transport in the meridional (N-S) direction, which transports the warm water outside the equatorial region that results in the build up of heat in the equator.
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  10. This discussion shows how bad indicator the average temperature is. In many systems, average surface temperature is not directly correlated with internal energy, barring the case of an isothermal copper sphere (and the Earth is obviously not an isothermal sphere).
    * plug a fridge : the average surface temperature will increase and the internal energy content will decrease
    * red giants are cooler than main sequence star but their thermal content is higher

    of course Earth temperature will not vary so much, but still, variation of tenths of degrees can occur without net energy change and even without energy budget change (people often confuse the energy content with the energy flow ) During an intense El-niño -La Niña cycle, average temperature vary by 0.5 °C or more - that is 40 years of supposed anthropic warming ! this can not of course be attributed in a change of the same energy content . Discussing whether the energy content has varied or not is immaterial : it's just uncorrelated, because variations occur mainly through redistribution of temperatures. The point of climate models is that they assume that above 30 years, no spontaneous variation can occur without a change of forcings. But, to my knowledge, there is absolutely no scientific demonstration of this - it is just an assumption.
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  11. johnd #92

    I'd love to carry on the discussion, whenever you have the time.

    You say:

    Examining the uncertainties and limitations of our current far from complete understanding, and how those limitations has a substantial impact on the global climate predictability.

    Those uncertainties are well known and openly discussed, too. Those who use the available mainstream science are able to make some pretty good projections. The competing theories have trouble fitting in all the data.

    John, I'm no expert. I don't even work in this field. After your last post I think you don't either. If you do not understand the relevance of those questions, I suggest you at least try, or ask. There are lots of pretty qualified people here that have shown to be delighted in answering any honest question asked.
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  12. At the end of the day, the"skeptic" tactic of conflating weather and climate to confuse lay people is scientifically wrong and a red herring. "Skeptics" here either seem to be trying to detract from that disingenuous tactic by their camp or worse yet, are defending it.

    ENSO is transient and has been shown to play very little role in modulating long-term temperature trends. See Foster et al. (2010):

    "The suggestion in their [McLean et al. 2009] conclusions that ENSO may be a major contributor to recent trends in global temperature is not supported by their analysis or any physical theory presented in that paper, especially as the analysis method itself eliminates the influence of trends on the purported correlations."

    Foster et al. go state in their conclusions that:

    "It has been well known for many years that ENSO is associated with significant variability in global mean temperatures on interannual timescales. However, this relationship (which, contrary to the claim of MFC09, is simulated by global climate models, e.g. Santer et al. [2001]) cannot explain temperature trends on decadal and longer time scales."

    So I challenge skeptics here to, instead of pontificating and talking through their hats, publish a paper which successfully challenges/refutes the findings of Foster et al. (2010).
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  13. Alexandre at 22:39 PM, to avoid getting side tracked we will need to keep reminding ourselves of the topic of this thread, and also that the paper I referenced is relevant to that topic.

    Regarding your "pretty good projections", whilst I don't mind discussing such a short time frame, generally if anyone other than someone pro AGW introduces examples of less than 30 years, accusations of cherry picking resonate loudly.

    Your "pretty good projections" are based on a rise of 0.33°C in the global mean surface temperature increase(land and ocean combined) for the 16 years after 1990.
    My paper indicates the linear trends of global, terrestrial, and ocean mean SAT during 1982 to 2008 as being 0.14, 0.21, and 0.10°C per decade, respectively. This is based on data from the global NCEP Reanalysis which is made available for climate studies.

    So immediately there is considerable difference of opinion there.

    Next your study ties temperature and sea level rise directly to CO2.

    My study has this to say on page 6 --
    "With assimilating merely historical SST observations, the SINTEX-F coupled model
    reproduces realistic interannual variations and long-term trend of the global SAT during 1982-2008.
    The ENSO-related interannual signals and colder/warmer states before/after the 1997/98 climate shift are correctly captured."

    Regarding what might be driving such warming, the study notes "Whether the terrestrial warming might be caused by local response to increasing greenhouse gas (GHG) concentrations or by sea surface temperature(SST) rise is recently in dispute."

    What the researchers found as part of the study was that depending on the time frame being modeled, it was not necessary to include GHG's in order to find correlation.
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  14. johnd, you seem to have either slightly misinterpreted the Luo paper or deliberately quoted out of context. It proposes that short term enhanced land surface temperatures are driven mainly by Sea Surface temperatures (SST) and heat exchange, rather than directly by GHG and radiative effects. They show that short term (seasonal to interannual) variations in Surface Air Temperature (SAT) is driven mainly by SST (the topic of their paper). They also accept SST is a longer time constant function due to longer term natural variations superimposed on a warming trend due to radiative forcing and GHG. If true, this implies better predictability of regional SAT at periods of over a year by using SST conditions to initialise the models. Some quotes from the paper:

    “We note that the SST warming itself may be driven by both the increasing GHGs forcing and slowly-varying natural processes (Solomon et al. 2007). The SST change was found to play a dominant role in determining the land/ocean warming contrast probably via complex hydrodynamic-radiative teleconnections”.

    “Considering large uncertainties in local climate response to GHGs forcing but relatively robust response of the global mean temperature (Solomon et al. 2007), here we examine potential influence of the trend of global mean surface temperature on climate predictability at lead times of up to 2 years”.

    “The warming trend in the tropics, partly due to the increasing GHGs forcing (Liniger et al. 2007), is about two-thirds of the global warming (Fig. 7b).”

    And the last sentence of their conclusion: “The intrinsic predictability of global warming, which is arisen from the long memory of ocean warming, provides hope for enhanced prediction of climate anomalies (interannual variations + warming trend) under the increasing GHGs forcing”
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  15. Peter Hogarth at 07:07 AM, I think you will find that one of your excerpts from the paper is the same as one I offered earlier.

    I find that one has to be careful to understand whether at various points they are examining what influences are being manifested in the physical world or in the modeling.

    I am not sure what the points are of your last two comments. Can you elaborate.
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  16. johnd at 08:11 AM on 29 March, 2011

    If you are agreeing with the authors that GHG forcing is driving longer term global trends in SST and SAT, but shorter term variations in (primarily) tropical SST may in turn be driving corresponding interannual variations in SAT (such as the well known connection between ENSO or tropical SST variations and global SAT variations), then I have misunderstood your point in the final section of 116 and duly apologise. If I rephrase to clarify:

    If the time frame is long, it is necessary to include GHGs to get correlation.
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  17. johnd #116

    Yes, Rahmstorf compares those 16 years of observations with the early IPCC projections, and finds they were pretty good. And yes, he also acknoledges the short period - although that's not cherry picking, since he used all the available period.

    Your paper has not been tested against such a long period, so I'm not sure why you're so prompt to dismiss the mainstream (successful) science. Besides, the japanese paper does not deny the GHE long term importance.

    Again: the obstruction of IR radiation by GHG is well established, well known and observed. The better modelling of ocean circulations is an important work that will improve interannual and decadal predictions - it does not contradict the GHE.

    I stress you avoided to answer any question regarding the evidence supporting the consensus (lack of time).
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  18. Alexandre at 22:43 PM, I think the JAMSTEC paper is attempting to address most of the difficulties the Rahmstorf paper notes, in being able to produce reliable, and thus useful climate projections.

    One aspect this introduction of the Rahmstorf study reveals, is the necessity to consider the difference between data sets used by different researchers.

    Rahmstorf used a rise of 0.33°C in the global mean surface temperature over the 16 years whereas JAMSTEC using NCEP would have used 0.22°C based on a trend of 0.14°C per decade determined over the period 1982 to 2008.
    This is a huge difference, particularly when being used to project trends.

    If the NCEP data was used instead in the Rahmstorf study it would appear that the lower temperature trend would have required the study to focus on the lower areas of uncertainty within the IPCC projections rather than the upper areas as it has done.

    What differences do you see the use of the NCEP data would have made to the study?

    It would be interesting to see if the error bands of the different trends overlap, if they did, one would be left wondering of their usefulness, if not, the possibility that either one of the two is not a valid representation, or maybe even both.

    JAMSTEC are not seeking to overturn any accepted basic principles, they acknowledge all known contributing factors.
    I interpret this paper as not attempting to eliminate any of the factors that combine to produce a changing climate, but rather identify which of those play key roles and in what order of importance under varying circumstances.

    This thread is about the prediction of weather as compared to the prediction of climate. I feel the JAMSTEC paper ties the two together.
    It is all very well to make projections about what the average global climate may be at some distant time, but what is most important is to know how it is going to manifest itself specifically in different regions.
    As is hardly necessary to do, the JAMSTEC paper shows that there is still a lot of uncertainty of what are all the contributing factors that causes our existing climate to manifest itself in the ways it does in the here and now.

    To alleviate your apparent stress, I guess these are the questions you are referring to.
    What ocean oscillation became suddenly warmer now then on the last millennium or two?

    - Why did the outgoing longwave radiation diminish on the last decades?

    - Why did backradiation become more intense?

    - Why did IR radiation trapped by GHG have no effect on temperature this time?
    ......

    I'm not certain that anyone can adequately answer such questions.

    The current understanding is that there is an energy imbalance at the TOA, and the surplus is , well, missing.
    Until such time the understanding of the processes involved are such that the energy budget can be balanced, then we can only speculate.

    What I am more interested in is that other threshold that energy has to cross at the surface.
    Of one thing I am certain, any solar energy that may be sunk by the oceans is firstly subject to the conditions that control that surface threshold, before it can even expect to cross the threshold at the TOA.
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  19. johnd at 13:23 PM on 30 March, 2011

    You say:

    Rahmstorf used a rise of 0.33°C in the global mean surface temperature over the 16 years whereas JAMSTEC using NCEP would have used 0.22°C based on a trend of 0.14°C per decade determined over the period 1982 to 2008.

    This part of your answer (along with a few other bits) makes me wonder if you understood what that Rahmstorf paper is all about. He's not projecting anything, nor is he hindcasting.

    He did not "use the upper areas" of uncertainty nor the lower ones. He just juxtaposed observations and projections, with the whole uncertainties, and compared them.

    And the observations match those projections pretty well. My untrained eye would even say that global temperatures are closer to the upper limit of uncertainty ranges than the lower (of course, so are emissions as well). So, if the IPCC (not Rahmstrof) had used an even lower projected warming rate, as you suggest, it would yield poorer results. Have a look:



    Of course, 16 years is not long enough for such a noisy signal, but so far, so good. And if you add the 3 last years, the projection is still just as good. We should keep watching this, but nothing here suggests the IPCC should have thought it would warm less.

    About your other point:

    The current understanding is that there is an energy imbalance at the TOA, and the surplus is , well, missing.

    Maybe you are confusing energy balance at the TOA with the climate heat content?

    The radiative difference is not missing. It's radiating back down, as predicted and observed.
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    Moderator Response: [mc] fixed image width
  20. Alexandre at 02:35 AM, if we are to accept that two trends determined from each data base as absolute, then obviously either the temperature at one, or both, ends of the time period used are different.

    If it is such that the error range of each data base is so large that they overlap, that would make any discussion involving such small temperature differences meaningless.
    So which do you think accounts for the differences?

    On the matter of the energy imbalance, what you are referring to is something different.
    The energy imbalance is so small it cannot be directly measured at the TOA. Instead it is inferred by trying to account for all the heat within the system. Unfortunately the bottom line only balances with a portion entered as missing.
    Without being to accurately quantify all the heat, the baseline remains unknown. (perhaps a bit like the matter regarding the trends mentioned above)
    This has been discussed in a number of threads,"Tracking the energy from global warming" being one that you could reference.
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  21. Climate vs weather.

    A group of activists headed up to the arctic circle in May 2009 to "raise awareness" that the "warmer climate" was creating mild snow, ice, and temperature conditions there, thus driving polar bears to extinction.

    They were driven back by ferocious snow, ice, and temperature conditions that nearly killed them; they needed to be rescued lest they die under the horrific cold conditions they found on the way. The number of polar bears they encountered was posing yet more deadly risk to the party.

    It incident was all due to colder "weather" and not the warmer "climate"



    http://blogs.telegraph.co.uk/news/jamesdelingpole/9802307/Global_warming_explorers_in_Arctic_get_nasty_shock_polar_ice_caps_blooming_freezing/
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    Moderator Response: Yes exactly, as you pointed out this is an example of weather not climate. If your argument is that the arctic is not warming, please take it to one of the related Arctic threads posted here.
  22. Bruce@124 If you think there is anything interesting in that, you have just demonstrated that you don't understand the difference between weather and climate. A warming climate does not imply there will not be bad weather, there isn't anything ironic about it. Dellingpole shows rather poor taste in his sarcastic gloating about it IMHO, I don't know why anyone would want to share in that.
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  23. Muoncounter, thanks for the invitation. The distinction between weather and climate relevant to global warming is the what affects the mean flow of energy at TOA on a global basis. The current change in CO2 forcing and the forcings in this graph: /news.php?n=1025#64969 change the climate. OTOH weather responds to cyclical changes in forcing, diurnal and seasonal being obvious and ENSO being less cyclical and less obvious. The current southward movement of the polar jet is purely weather because it will move back north next spring. If it does indeed move further north in the summer that would be a climate effect of AGW. I do not believe that is yet evident.

    One of the numerous climate effect of the ice sheets is a southward movement of the polar jets in the NH and northward movement in the SH. This causes various changes in weather which result in permanent (or semi-permanent) changes in the mean flow of energy at TOA. The specific one in the paper I linked here /news.php?p=1&t=55&&n=1025#64963 was that the poleward movement of the polar jet was a large factor in the transition from glacial to interglacial, IOW weather change causes climate change.

    Editorial note: I agree I should not gum up the Pielke thread debating weather versus climate or forcing versus feedback. However there are points Pielke made that are not being directly addressed, namely his contention that the glacial climate regime (read weather regime) is very different (result is net cooling); and his other contention that the global average temperature (as shown in the diagram (first link above) is skewed by the increase in elevation due to the ice sheets. Each point should be clarified and addressed. His writings may sometimes contain different usages of terms, so I was also trying to clarify terminology with my posts (and I may or may not have been correct).
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    Response:

    [DB] Dr. Pielke's points are noted and will be addressed.

  24. Eric (skeptic) - "The distinction between weather and climate relevant to global warming is the what affects the mean flow of energy at TOA on a global basis."

    Please do not forget that changes induced by temperature shifts are feedbacks, not forcings. If long term weather patterns change due to temperature shifts, and (a second step, requiring some evidence) change TOA imbalance, they are feedbacks, part of the climate sensitivity. Which again is estimated by looking at initiating radiative imbalance and the resulting temperature changes, roughly 3-3.5C/doubling of CO2, or 3-3.5C for 3.7 W/m^2 forcing imbalance.
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  25. Eric#123: "weather responds to cyclical changes in forcing, diurnal and seasonal being obvious and ENSO being less cyclical and less obvious."

    Agreed. But your contention was, if I understand correctly, that weather changes are both 'semi-permanent' and a forcing for climate change. Maybe this is a semantic question, but how are seasonal cycles 'semi-permanent'? And how can cycles, which are in response to energy imbalances, be considered 'forcings'?

    Do you consider ENSO a forcing? If la Nina is a cause for the Texas/New Mexico/Mexico drought, are we now in a 'semi-permanent' drought?
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  26. KR, a permanent shift in the jet stream (southward in the NH) due to ice sheets growing in the NH is a forcing just like the change in (global average) albedo caused by the ice sheets. It must therefore be added to the diagram that was shown in the Pielke thread that claims the only forcing is from ice albedo and GHGs. If the southward migration of the jet (NH) only caused more snow and a larger ice sheet, then the chart in the diagram would be correct. If the change in jet configuration were due merely to temperature changes specifically GAT, that chart would be more or less correct. But neither of those conditions is true. Also that diagram is missing forcing from dust.

    In short, the estimates of the first order forcing effects of ice sheets must include the permanent changes in weather, not just ice and snow albedo changes. There are many papers on the topic of LGM climate discussing LGM weather. Among the cooling influences are increased meridional flow (more heat loss in higher latitudes) and increased water cycle (although that one less certain). Here's one such paper: http://www.cnrm.meteo.fr/recyf/IMG/pdf/Laine_et_al09.pdf noting that the results are very model-dependent.

    The two consequences of permanent weather change forcing is that the diagram in the Pielke thread is incomplete and the CO2 change sensitivity cannot be calculated statically. Thus it requires the same models used for modern climate sensitivity studies, except with much more uncertainty since modern studies can be verified against present-day weather and paleo-weather models cannot. Another consequence is that the paleo sensitivity evidence is not an independent line of evidence, but another use of the same models used for modern sensitivity derivations.

    Muoncounter, seasonal cycles show that weather is a feedback to solar-driven temperature changes. But for the glacial period, summer is gone, replaced by a short rainy season. The cause of the change is the ice sheets, specifically their orographic and local temperature effects. Note that is not global temperature or average temperature or anything that can be used to estimate sensitivity but a specific local temperature contrast between the cold ice sheet and the warm land areas, a southerly jet with a stronger storm track.

    I should have used clearer language. The change in paleo weather varies by season and there are seasonal cycles. But the change is secular. ENSO is is mostly a cycle that redistributes heat between parts of the ocean and atmosphere and then reverses and returns the heat to the source. But ENSO can also exhibit secular changes that amount to a forcing. As a simple hypothetical example, if we entered a regime of El Nino all the time then we would have less outgoing longwave radiation all of the time and thus global warming and in that (hypothetical) case, ENSO would be a forcing. The connection is that ENSO modulates precipitation (El Nino = more precip) and precip is negatively correlated with OLR. Regional differences are quite pronounced so it can be a bit difficult to see the global effect.

    La Nina is a major cause for the Texas drought. If we entered a semi-permanent La Nina, then Texas would have a semi-permanent drought all other things being equal.
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  27. Eric (skeptic), what was the net (down minus up) change in irradiance at the tropopause at the LGM due to the change in the position of the northern polar jet stream?

    I am not raising an issue of uncertainty here. Rather, I am raising a definitional issue. The radiative forcing is defined by the IPCC as follows:

    "The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values."

    (quoted from wikipedia.)

    Patently, a change in the position of a jet stream will make no direct difference to the net irradiance at the top of the troposphere. As such, if treated as a forcing, then its forcing is, always, 0 W/m^2. Hypothetically such a change could result in more snow or ice, resulting in a higher albedo, but those changes would all be feedbacks and hence not part of the forcing.

    So, even if it where appropriate to treat a change in jet stream position as a forcing, adding its value to the graph would not change by an iota the estimate of the climate sensitivity.

    This is if you persist in ignoring the logical point that changes to the position of the jet stream is a response to temperature changes, and hence part of the feedback system.
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  28. Eric (skeptic) @126, a condition of permanent El Nino would increase OLR, not decrease it. If conditions could maintain the El Nino permanently, this would be compensated for by other cooling effects elsewhere in the climate to restore the OLR to the equilibrium level. More likely, the excess loss of energy to space would result in a termination of El Nino conditions.

    I should note that El Nino is associated with precipitation in some areas (Eastern Australia), but with a lack of precipitation in others (New Zealand, Peru), so your simple mechanism of El Nino => increased water vapour => reduced OLR does not work. On the other hand, El Nino's are associated with extended hot surface waters on the Pacific, which means the mechanism El Nino => warm water => increased upwelling radiation => increased OLR does work.
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  29. Eric#126: "for the glacial period, summer is gone,"

    That's a bit of an over generalization; summers may be shorter, but they are not absent. All that is necessary for glacial advance is an excess of snowfall/accumulation over summer melt. That does not require that 'summer is gone.' The glacial margin areas of New England the upper Midwest have many varved clay deposits, sedimentary evidence of winter/summer cycles. In addition, the Gulf of Mexico has a large column of sediments deposited during the glacial stages, carried south from glacial margin runoff by shortened versions of the rivers we see today.

    "if we entered a regime of El Nino all the time ... ENSO would be a forcing."

    We must not be using the same definition of 'forcing.' A cyclical response mechanism, driven by an uneven distribution of heat cannot (as I understand the word) be a 'forcing.' The primary forcings are those agents that either trap heat (ie, GHGs, black carbon), alter insolation (solar variation, orbital parameters, etc) or change albedo (aerosols, etc).
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  30. Tom, your point is valid, namely that a forcing must make a direct and permanent difference in the TOA radiative balance. I believe the position of the polarjet passes that test in several ways. The main one is that a meridional jet will transfer more heat to higher latitudes to be radiated away. In the general, the further south the polar jet, the higher amplitude the long waves within it. The redistribution of heat will directly raise the global net outgoing-incoming radiation.

    On El Nino, Tom, your points are very valid. I mentioned the regional differences of El Nino around the globe. Despite those offsetting differences, the net effect is to increase outgoing-incoming. I should have also mentioned the relative increase in warmer SST area and increased OLR from that. I am not sure how a permanent El Nino could be compensated for elsewhere, where is elsewhere?

    muoncounter, your definition of forcing seems to match Tom's, namely a change in albedo or a change in trapped heat. I believe that is a bit too narrow as I explained above. Specifically the uneven distribution of heat that you maintain is not a forcing can be a forcing if there is a permanent change causing it that is not an effect of a average temperature change. If, as a hypothetical example, we slow the spinning of the earth, the lengthening of the diurnal cycle will cause an average global temperature increase as night temperatures tend to have a lower limit but day temperatures would rise relatively more (ignoring other potential effects of a slowing rotation). But that would be a forcing because it causes a change in temperature even though it doesn't directly change radiation or albedo.
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  31. Last October (sorry for the delay) Tom said: "changes to the position of the jet stream is a response to temperature changes, and hence part of the feedback system."

    The problem with that logic is that the changes to the position of the jet in response to temperature (more precisely other factors like the continental ice sheets which respond to temperature) when transitioning between glacial and interglacial are completely different from the changes to the jet when transitioning from the present climate to the CO2-doubled climate. There is no way to apply the sensitivity derived from the paleo weather changes to today's weather changes.
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