Bishop Hill +++Climate sensitivity is low+++
Dec 19, 2012 Climate: sensitivity Matt Ridley has an article in the Wall Street Journal which is of incalculable importance.
Mr. Lewis tells me that the latest observational estimates of the effect of aerosols (such as sulfurous particles from coal smoke) find that they have much less cooling effect than thought when the last IPCC report was written. The rate at which the ocean is absorbing greenhouse-gas-induced warming is also now known to be fairly modest. In other words, the two excuses used to explain away the slow, mild warming we have actually experienced—culminating in a standstill in which global temperatures are no higher than they were 16 years ago—no longer work.
In short: We can now estimate, based on observations, how sensitive the temperature is to carbon dioxide. We do not need to rely heavily on unproven models. Comparing the trend in global temperature over the past 100-150 years with the change in “radiative forcing” (heating or cooling power) from carbon dioxide, aerosols and other sources, minus ocean heat uptake, can now give a good estimate of climate sensitivity.
The conclusion—taking the best observational estimates of the change in decadal-average global temperature between 1871-80 and 2002-11, and of the corresponding changes in forcing and ocean heat uptake—is this: A doubling of CO2 will lead to a warming of 1.6°-1.7°C (2.9°-3.1°F).
Warming at a snail's pace is a small problem, not a big one.
The Wall Street Journal is paywalled, unless you go via Google. Click here and then click on the first entry on the search results.
Reader Comments (56)
shub,
"The yellow line shows no variability whatsoever. Which means, in the models, its contribution to the formula above should be minimal, or zero?"
I'm not sure, but if the graph is showing what I suspect, the slope in it is because of the changing balance between surface and deep ocean warming. It's all to do with the difference between transient climate response and equilibrium climate sensitivity.
The simple concept of 'sensitivity' is actually a simplification of more complicated behaviour. The sensitivity varies with timescale and probably with temperature, involves time delays and memory effects, and stuff we don't understand. I think Nic Lewis has alluded to this a time or two in his previous discussions. One of the problems with using observations from the satellite record to estimate sensitivity is that it only estimates the *short term* sensitivity, on the scale of months or years. The sensitivity over decades and centuries might be different - and indeed I have a vague recollection of someone saying that's how the models behaved. They had a lower apparent sensitivity over months than they had long-term. But don't quote me on that.
Dung: what I wrote was totally on topic. You wrote condescendingly of Ridley being as wrong as the IPCC. I assume you feel your own sentence was on topic. If so then so was my response, indicating that I trusted Ridley and Lewis a lot more, from experience, than you and most other greenhouse doubters around here. This is nothing personal - I just don't have a high opinion of your judgment on the science in this area and on the right way to bring forward effective criticism of the IPCC, in order to improve AR5. I think Matt and Nic have got it exactly right. So completely on topic and nothing personal, so please don't take it that way.
Richard, Dung
Take it somewhere else.
There isn't anything to take.
IIRC, Professor Richard Lindzen expressed the opinion that a doubling of CO2 would produce a warming of about 1.4 C about one decade ago.
It is aerosols that are the big unknown, and it would appear that they have been used to date as a fiddle factor.
All the data sets are unreliable and not fit for purpose, but probably the best quality data set is the satelitte temp records. Unfortunately, this data set is rather short to have full confidence in extrapolations.
The satelitte data set shows that in the past 33 years temperatures have not risen as a consequence of the additional CO2 emitted during that period (which is approximately 2/3rds of all manmade CO2).
The temperatures were flat between '79 amd '97 and flat between '99 and 2012. There is only a step change in and around the supoer El Nino of '98 and unless CO2 somehow caused that El Nino (and no one has suggested a mechanism whereby CO2 could cause that result), the inescapable conclusion is that the temperature sensitivety in the present state of Earth's environ is statistically zero (or so unmeasurably low that no CO2/temp fingerprint can be found in the satellite record).
As the staelitte record lengthens and if this record continues to show a flat temperature stasis (possibly only interupted by El Nino type events), it will become more and more obvious that sensitivity is close to zero. The team can make whatever adjustments they wish to make to the land based record but if that record gets too far out of kilter with the satelitte record, it will look rediculous (if not suspicious).
There are any number of reasons why sensitivity may be close to zero such as for practical purposes the atmosphere is fully saturated at about the 370ppm CO2 level such that an increase in CO2 above that figure has no or all but no effect, or it may be that there are significant problems with the 'basic physics' possibly that DWLWIR lacks sensible energy and for example cannot heat the oceans, or other such similar issues. Obviously black carbon is altogether a different issue, and it may be that black carbon is partly responsible for ice and glacial melts.
As I said, the above is dependent upon the true effect of aerosols. I envisage that when accurate and relaible data is in, it will be seen that sensitivity is significally below the levles that even Ridley is suggesting.