On Nov 25, 2009, at 8:19 AM, Bill Powers wrote:
> Guys (& Gals):
>
> I've got a few questions about the human influence on global climate warming. This issue has become such a political football and both sides of the ball that I can't tell what to believe or even to suspect.
>
> 1) Is it certain that global climate warming is taking place?
Yes.
> 2) How is this determined (e.g., average terrestrial albedo, satelite SST, etc.)?
All of the above. Whether it's surface stations or SST measurement, or radiosonde measurements or satellite measurements (once you correct for reading the stratosphere's temperature in the mid-troposphere) all over the world shows warming. That's what it's called GLOBAL warming.
> 3) It seems to me that we have terrestrial data of varying quality over something like 50 years, esp. with the advent of satelite remote sensing. I know this data is noisy, but I had thought that there was persistent and evident trend. Is this so. Yes in
It has and the data has gotten less noisy. The way you deal with noise is measure over a greater time since most of what we call noise is actual cyclical variation. As long as you keep the amount of time long enough you can measure the trends.
> 4) I've been hearing that climate warming has significantly leveled off over the past ten years or so. Is this so? If it is, how is this consistent with recent assertions that we are losing glacial ice at increasingly alarming rates. There can't be that long of a time lag.
The rate of increase has leveled off in the current decade. Still, eleven of the last twelve years are the warmest in the last 150. There are large decadal length factors that can hide the overall trend, particularly the El Nino Southern Oscillation. 1998 was the El Nino of the century. If you mark your ten year trend arbitrarily starting in 1997, 1998, and 1999 you get radically different answers. 1998 was an outlier way above the trendline.
The "lag" you are referring to is the fact that the oceans store heat. Right now we are experiencing the effects of carbon put in the atmosphere 20-30 years ago. From an electrical engineering standpoint it's a capacitor. Getting back to the noise question a capacitor filters it out. One key fact is the Southern Hemisphere has more ocean than the Northern Hemisphere. What happens is the warming trend is less pronounced but also less noisy in the SH. That's why I look at the SH for any trends and sho' 'nuff the SH continues to a slower but continued warming trend. Climate skeptics ask why is the Arctic is melting while the Antarctic is not. It's because of this effect that the computer models predict that Antarctica would be stable for decades to come. Then came the scary part. Antarctica is melting at a faster rate than it should be. The GRACE satellite measurements showed large amounts of ice loss. See page 28 here. http://www.ccrc.unsw.edu.au/Copenhagen/Copenhagen_Diagnosis_HIGH.pdf So, there is legitimate concern that the computer models may not be accurate enough but so far when we compare the models against reality the models have underestimated the problem. Another thing that should be noted is computer models do well only when the predicted state is nearby to the current state. Paleoclimate research has shown that if we are 3-6 degrees higher than now we enter a "different planet" regime but unlike previous such warming periods we will be entering it three orders of magnitude faster than we ever have in the history of our planet. So, if we do the experiment and enter this "planet" we will be flying completely blind.
> 5) Assuming that global warming is reasonably well established, we can expect that there will significant discussion of the causes. Is the debate primarily about the effect of human activities on global warming?
That's not debated either because the different kinds of warming have different "signatures". For example, if the warming was due to solar variability the stratosphere and the surface would both warm. If on the other hand it was due to AGW the surface will warm faster than the stratosphere and there will be polar amplification where the poles heat faster than the temperate regions. We have observed the latter. This is the reason why in 2009 when the AGU, one of the largest earth science societies, when polling its members who publish peer-reviewed articles in climatology 97% stated that anthropogenic global warming was true.
> 6) In what manner is the effect of human activity assessed? Is it primarily through computer modeling?
No it's through direct observation and measurement now. The amounts of CO2 is measured as well as temperatures at the various altitudes. Downward looking satellites as far back as the early 60s saw the telltale signature of the greenhouse effect of CO2. This was how water, which is also a greenhouse gas, was acquitted of the warming that was already seen back then. AGW is properly a theory in that it has know and understood physical mechanisms of why things are happening the way they are. CO2 causing warming was first posited by Svente Arrhenius in 1898(!). What changed was ever better computer modeling. But as I noted above the computer models are never "good enough". (It's good enough, though, to completely reconstruct the entire 20th Century instrumental record.) This is an important way the science advances when there is a disconnect between the model and the measurement then the model is examined and improved along with greater understanding of the underlying mechanisms. Then lather rinse repeat.
> 7) It seems that at least some of the "cover up" identified with these hacked emails is the apparent slowing of global warming. Is this true?
In 1998, there was a disconnect between one set of tree ring data and everything else. The e-mails in question should be interpreted in the context of what do you do with the outlier problem. Sometimes the outlier completely invalidates everything else but more often than not it doesn't. When you see the word "real" in the e-mails this is the instrumental record which is far more accurate and precise than a proxy record. I understand people being critical of the proxy data what I don't get is preferring it to the instrumental data in order to prove a non-existent cooling. Remember this was 1998 before the earth "cooled"! If this was a cover up it was a really lousy one. In the intervening decade from the e-mails we now have a more accurate instrumental record, better computer models, and many more and more accurate paleoclimatic proxies and much better techniques. One of the results of the problem above is that many of the paleoclimate research papers do their analysis twice, both with and without tree ring data and when they get the same answer they get a more robust solution. One of the ways scientific consensus is reached is when the same answer happens from multiple sources. This happened for the paleoclimatic data when it was tested in different ways the "hockey stick" survived and went from a leading edge paper in 1998 that might well be wrong to a firmly established consensus. The fact there were problems with the data back then pushed the science forward. For example:
Mann ME, et al. (2008) Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. Proc Natl Acad Sci USA 105:13252–13257.
Luterbacher J, Dietrich D, Xoplaki E, Grosjean M, Wanner H (2004)European seasonal and annual temperature variability, trends, and extremes since 1500. Science 303:1499–1503.
Wahl ER, Ammann CM (2007) Robustness of the Mann, Bradley, Hughes reconstruction of surface temperatures: Examination of criticisms based on the nature and processing of proxy climate evidence. Clim Change85:33–69.
Mann ME, Rutherford S, Wahl E, Ammann C (2007) Robustness of proxy-based climate field reconstruction methods. J Geophys Res112:D12109.
Osborn TJ, Briffa KR (2006) The spatial extent of 20th-century warmth in the context of the past 1200 years. Science 311:841–844.
The abstract of Wahl and Amman is representative of many of the papers:
The Mann et al. (1998) Northern Hemisphere annual temperature reconstruction over 1400–1980 is examined in light of recent criticisms concerning the nature and processing of included climate proxy data. A systematic sequence of analyses is presented that examine issues concerning the proxy evidence, utilizing both indirect analyses via exclusion of proxies and processing steps subject to criticism, and direct analyses of principal component (PC) processing methods in question. Altogether new reconstructions over 1400–1980 are developed in both the indirect and direct analyses, which demonstrate that the Mann et al. reconstruction is robust against the proxy-based criticisms addressed. In particular, reconstructed hemispheric temperatures are demonstrated to be largely unaffected by the use or non-use of PCs to summarize proxy evidence from the data-rich North American region. When proxy PCs are employed, neither the time period used to “center” the data before PC calculation nor the way the PC calculations are performed significantly affects the results, as long as the full extent of the climate information actually in the proxy data is represented by the PC time series. Clear convergence of the resulting climate reconstructions is a strong indicator for achieving this criterion. Also, recent “corrections” to the Mann et al. reconstruction that suggest 15th century temperatures could have been as high as those of the late-20th century are shown to be without statistical and climatological merit. Our examination does suggest that a slight modification to the original Mann et al. reconstruction is justifiable for the first half of the 15th century (∼+0.05∘), which leaves entirely unaltered the primary conclusion of Mann et al. (as well as many other reconstructions) that both the 20th century upward trend and high late-20th century hemispheric surface temperatures are anomalous over at least the last 600 years. Our results are also used to evaluate the separate criticism of reduced amplitude in the Mann et al. reconstructions over significant portions of 1400–1900, in relation to some other climate reconstructions and model-based examinations. We find that, from the perspective of the proxy data themselves, such losses probably exist, but they may be smaller than those reported in other recent work.
This is not to say there is not a coverup. See the following investigation by the NASA IG about a real coverup of climate science:
http://oig.nasa.gov/investigations/OI_STI_Summary.pdf
The IG also manages freedom of information requests and this report was after the original request was made in 2007. The IG must have believed that there was no coverup by the scientists, just the White House.
Rich Blinne
Member ASA
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Received on Wed Nov 25 12:09:22 2009
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