Tuesday, September 26, 2006

Well lookee that....

Hansen, Sato, Ruedy, Lo, Lea and Medina-Elizade have published their latest screed on "Global temperature change" in the Proceedings of the National Academy of Sciences.

and if you actually use the GISS or the Hadley Center temperature records the agreement is excellent. Of course, if you want to falsify the prediction, you can always engage in climate fraudit, straight out denial is also a popular sport in comments sections as well. Eli has had a series of posts on the Hansen paper and testimony in 1988 where the original prediction was made (the graph above is an update of that one, with the same model predictions and data up to 2005). The new paper says (about the old predictions)

Observed warming (Fig. 2) is comparable to that simulated for scenarios B and C, and smaller than that for scenario A. Following refs. 18 and 14, let us assess ‘‘predictions’’ by comparing simulated and observed temperature change from 1988 to the most recent year. Modeled 1988–2005 temperature changes are 0.59, 0.33, and 0.40°C, respectively, for scenarios A, B, and C. Observed temperature change is 0.32°C and 0.36°C for the land–ocean index and meteorological station analyses, respectively.....
Not bad for a first generation model, and they got a lot of other things right too. Now this does not say the model was perfect, just that it was useful, moreover there are good scientific reasons why it worked, including good physics, and a relatively short period between then and now.
Close agreement of observed temperature change with simulations for the most realistic climate forcing (scenario B) is accidental, given the large unforced variability in both model and real world. Indeed, moderate overestimate of global warming is likely because the sensitivity of the model used (12), 4.2°C for doubled CO2, is larger than our current estimate for actual climate sensitivity, which is 3 1°C for doubledCO2, based mainly on paleoclimate data (17). More complete analyses should include other climate forcings and cover longer periods. Nevertheless, it is apparent that the first transient climate simulations (12) proved to be quite accurate, certainly not ‘‘wrong by 300%’’ (14). The assertion of 300% error may have been based on an earlier arbitrary comparison of 1988– 1997 observed temperature change with only scenario A (18). Observed warming was slight in that 9-year period, which is too brief for meaningful comparison.
14 is Michael Cricheton, 18 is Pat Michaels.

In the period between 1988 and 2005 CO2 concentrations increased about 30 ppm, or about 1/10th of that equivalent to a doubling. Thus, the higher assumed climate sensitivity (~40% high) would only result is a ~4% difference in the forcing if you assume a linear trend, less if you use the proper logarithmic dependence of CO2 forcing on CO2 mixing ratios. I think Hansen et al are being much too modest.


M.J. S. - (Wacki) said...

ugh....... the fate of the world rests on getting quality information out and the NAS makes people pay to see this article. And people wonder why scientists havea tough time fighting misinformation campaigns.

Anonymous said...

Hansen may have got it right, but as we all know from Roger Pielke, Jr, he "got things right for the wrong reasons":

"With respect to Jim Hansen’s 1988 predictions, his Scenario C88 was the most accurate with respect to emissions 1990-2000. That scenario froze time in 2000, meaning that going forward there are two evolving scenarios which both have dramatically overestimated emissions [emphasis added]. The lower of the two [scenarioC] is thus “more accurate” than the other. Neither is particularly accurate or realistic. Any conclusion that Hansen’s 1988 prediction got things right, necessarily must conclude that it got things right for the wrong reasons. [emphasis added]"


EliRabett said...

Sorry anon, RPJr is a political scientist and can neither add nor multiply. Hansen got pretty close to the actually forcing over the last 18 years.

Roger can argue that the C senerio was better until 2000, but it was only slightly better than the B, which Hansen called the most likely. Then again Roger is exaggerating to discredit Hansen. BTW that appears to be his cottage industry. Showing that Roger is a ton short of a clue is mine, and I have a much easier job.

B and C diverge noticeably only after ~ 2000 for the greenhouse gas concentrations and only after ~2005 in the global temperature or forcings. The principle difference being that emissions stop at 2000 in C. You can see this in the figure showing the forcings in the original paper.

Anonymous said...

It is clear from all your graphs showing GHG forcing that you have done a lot of work on this subject, which makes the following very interesting (at least to me):

Pielke posts a link to your graphs at the end of the comments section after his post and sites your work as a confirmation of his claims about Hansens predictions.

"His more accurate conclusions on the data are quite similar to mine (though I anticipate he may find some differences on N2O) and those published by Hansen in 1998, namely (a) Hansen’s 1988 scenarios generally overshot actual emissions, and (b) some errors in projecting individual emissions rates may have cancelled out, thereby making the total forcing projected more accurate."


EliRabett said...

I have noticed the tendency at Prometheus to make statements about links that are not bourne out by the links. This was one such case.

The reference to the information posted here was at the end of a long to and fro challenging Pielkes misreading of the Hansens paper in which the three scenerios were outlined.

At that time there was a concerted effort involving Michaels and others and pushed forward by Pielke to try and discredit Hansen's 1988 prediction. The proof that the prediction was correct is in the figure at the top of this post.

The key to understanding why it worked was well stated by James Annan in the thread you reference:

"This seems rather petty. Rather than looking at the details of every different GHG, it would be more meaningful to look at the overall forcing and how the climate responded to it. After all, predicting future CO2 (etc) levels is hardly in the domain of the climate scientists - but what we can tell you about is the relationship between emissions and climate change (with at least some degree of accuracy, as Hansen has shown). I've no doubt that if you were to re-run this model with observed GHG changes (and eg pinatubo in the right place), the output would match observations very well indeed.

Of course, it turns out that predicting the medium-term temperature change is a pretty easy thing to do - but we only know that through the work of climate scientists in understanding both how the climate responds to forcing, and how the anthropogenic forcing dominates natural effects."

To which I would add, that Scenerios B and C for CO2 match what actually happened very well, and that is the major forcing

M.J. S. - (Wacki) said...


I think your blog just made it on my "favorites" list. A quick question, in the models CO2 are the same for B & C up to 2010.


and up to 2010 there seems to be the same in CO2 forcing between B&C here as well:
graph 2

Yet the trace gases are very different. Is there an anthropogenic difference between A&B or is that difference considered "natural feedbacks"? Pre 2010 only of course.

M.J. S. - (Wacki) said...

ugh....... change my B&C's to A&B's. Sorry about that.

Hank Roberts said...

More info: the drop in anthropogenic emissions when the USSR collapsed was not only in CO2, but also in methane.


"... a new study by an international research team supports the suspicions of some experts that the leveling off was probably temporary and caused by a downturn in emissions from industry and most likely related to the collapse of the Soviet Union and its economy.

"After 1999, emissions from industry and other human activities began rising again, particularly in China, according to the study, which will be published today in the journal Nature. But that increase in methane from manmade sources appears to have been masked by a reduction in methane from sources in nature. Tropical droughts reduced methane released by bacteria in muddy wetlands, the study said."


Climate change: A nasty surprise in the greenhouse p405

The Kyoto Protocol aims to reduce emissions of greenhouse gases such as methane. But it seems that the fall in human-induced methane emissions in the 1990s was only transitory, and atmospheric methane might rise again.

Jos Lelieveld


Anonymous said...

But it seems that the fall in human-induced methane emissions in the 1990s was only transitory, and atmospheric methane might rise again."

Not only might human emissions increase, as Eli pointed out on an earlier post, a vast store of methane is trapped in the frozen soil of the arctic and, if released, it could dwarf future human releases.

The latter is a component of the "ticking time bomb of global warming" that Jim Hansen refers to. Once the methane starts being released in large quantities it may be an unstoppable deluge.

Tenney Naumer said...

Dear Eli,

Please, would you be so kind as to update the graph with the numbers through 2008 (my goodness! how did he know to get that plateauing in there?)?

And, also, I would not to copy it and post it on my blog, if you wouldn't mind.

Thanks so much,

Tenney Naumer