I have not been blogging climate much because none of the debates ever change. So here are some quick updates
- 67% to 90% of all warming in climate forecasts still from assumptions of strong positive feedback in the climate system, rather than from CO2 warming per se (ie models still assuming about 1 degree in CO2 warming is multiplied 3-10 times by positive feedbacks)
- Studies are still mixed about the direction of feedbacks, with as many showing negative as positive feedback. No study that I have seen supports positive feedbacks as large as those used in many climate models
- As a result, climate models are systematically exaggerating warming (from Roy Spenser, click to enlarge). Note that the conformance through 1998 is nothing to get excited about -- most models were rewritten after that date and likely had plugs and adjustments to force the historical match.
- To defend the forecasts, modellers are increasingly blaming natural effects like solar cycles on the miss, natural effects that the same modellers insisted were inherently trivial contributions when skeptics used them to explain part of the temperature rise from 1978-1998.
- By the way, 1978-1998 is still the only period since 1940 when temperatures actually rose, such that increasingly all catastrophic forecasts rely on extrapolations from this one 20-year period. Seriously, look for yourself.
- Alarmists are still blaming every two or three sigma weather pattern on CO2 on global warming (polar vortex, sigh).
- Even when weather is moderate, media hyping of weather events has everyone convinced weather is more extreme, when it is not. (effect explained in context of Summer of the Shark)
- My temperature forecast from 2007 still is doing well. Back in '07 I regressed temperature history to a linear trend plus a sine wave.
Much of the climate debate turns on a single logical fallacy. This fallacy is clearly on display in some comments by UK Prime Minister David Cameron:
It’s worth looking at what this report this week says – that [there is a] 95 per cent certainty that human activity is altering the climate. I think I said this almost 10 years ago: if someone came to you and said there is a 95 per cent chance that your house might burn down, even if you are in the 5 per cent that doesn’t agree with it, you still take out the insurance, just in case.”
"Human activity altering climate" is not the same thing as an environmental catastrophe (or one's house burning down). The statement that he is 95% certain that human activity is altering climate is one that most skeptics (including myself) are 100% sure is true. There is evidence that human activity has been altering the climate since the dawn of agriculture. Man's changing land uses have been demonstrated to alter climate, and certainly man's incremental CO2 is raising temperatures somewhat.
The key question is -- by how much? This is a totally different question, and, as I have written before, is largely dependent on climate theories unrelated to greenhouse gas theory, specifically that the Earth's climate system is dominated by large positive feedbacks. (Roy Spenser has a good summary of the issue here.)
The catastrophe is so uncertain that for the first time, the IPCC left estimates of climate sensitivity to CO2 out of its recently released summary for policy makers, mainly because it was not ready to (or did not want to) deal with a number of recent studies yielding sensitivity numbers well below catastrophic levels. Further, the IPCC nearly entirely punted on the key question of how it can reconcile its past high sensitivity/ high feedback based temperature forecasts with past relative modest measured warming rates, including a 15+ year pause in warming which none of its models predicted.
The overall tone of the new IPCC report is one of declining certainty -- they are less confident of their sensitivity numbers and less confident of their models which have all been a total failure over the last 15 years. They have also backed off of other statements, for example saying they are far less confident that warming is leading to severe weather.
Most skeptics are sure mankind is affecting climate somewhat, but believe that this effect will not be catastrophic. On both fronts, the IPCC is slowly catching up to us.
Dr. Roy Spencer has compared the output of 73 climate models to actual recent temperature measurements. He has focused on temperatures in the mid-troposphere in the tropics -- this is not the same as global surface temperatures but is of course related. The reason for this focus is 1) we have some good space-based data sources for temperatures in this region that don't suffer the same biases and limitations as surface thermometers and 2) This is the zone that catastrophic anthropogenic global warming theory says should be seeing the most warming, due to positive feedback effects of water vapor. The lines are the model results for temperatures, the dots are the actuals.
As Spencer writes in an earlier post:
I continue to suspect that the main source of disagreement is that the models’ positive feedbacks are too strong…and possibly of even the wrong sign.
The lack of a tropical upper tropospheric hotspot in the observations is the main reason for the disconnect in the above plots, and as I have been pointing out this is probably rooted in differences in water vapor feedback. The models exhibit strongly positive water vapor feedback, which ends up causing a strong upper tropospheric warming response (the “hot spot”), while the observation’s lack of a hot spot would be consistent with little water vapor feedback.
The warming from manmade CO2 without positive feedbacks would be about 1.3C per doubling of CO2 concentrations, a fraction of the 3-10C predicted by these climate models. If the climate, like most other long-term stable natural systems, is dominated by negative feedbacks, the sensitivity would be likely less than 1C. Either way, the resulting predicted warming from manmade CO2 over the rest of this century would likely be less than 1 degree C.
More on declining estimates of climate sensitivity based on actual temperature observations rather than computer models here.