Ultra-conservative report still concludes sea level rise could reach 6 inches a decade by century’s end! Deniers duped by leaker’s blunder.
Figure SPM.6.a. Warming in two IPCC scenarios reveals humanity’s choice. With aggressive action to reduce greenhouse gas emissions (RCP 2.6 with 443 ppm of CO2 in 2100), warming is modest and adaptation is plausible. With continued inaction (RCP 8.5 with 936 ppm in 2100), warming is a catastrophic and unmanageable 10°F over much of Earth’s habited and arable land — and more than 15°F over the Arctic. This projection ignores many key amplifying feedbacks, such as the release of permafrost carbon, which would likely lead to far greater warming.
The draft 2013 Fifth Assessment report of the Intergovernmental Panel on Climate Change leaked this week makes clear inaction on climate change would be devastating to modern civilization. The report finds that the human fingerprint on climate has grown more obvious, concluding “it is virtually certain” the energy imbalance that causes global warming “is caused by human activities, primarily by the increase in CO2 concentrations. There is very high confidence that natural forcing contributes only a small fraction to this imbalance.”
Yes, I know, the easily-duped deniers and their media stooges have reported the opposite is true, that solar forcing has been a significant driver of recent warming, but the deniers are as likely to be right as the flat earthers. The only question is why anyone still listens to them. I’ll repost a debunking of their nonsense below.
The draft Summary for Policymakers (the only thing 99% of people will ever read) finds:
It is extremely likely [">95% probability"] that human activities have caused more than half of the observed increase in global average surface temperature since the 1950s. There is high confidence ["About 8 out of 10 chance"] that this has caused large-scale changes in the ocean, in the cryosphere, and in sea level in the second half of the 20th century. Some extreme events have changed as a result of anthropogenic influence.
That multiply-hedged morass is pretty much the mildest statement that could possibly be made. A December 2011 study found it’s “Extremely Likely That at Least 74% of Observed Warming Since 1950″ was manmade; it’s highly likely all of it was (see Figure 1 below).
For me, the leaked draft, which has not yet been peer reviewed — and thus still has time to be watered down yet more – underscores how pointless the IPCC has become. Like the 4th assessment before it, this ultra-conservative and instantly obsolete report ignores the latest science — see “Fifth Assessment Report Will Ignore Crucial Permafrost Carbon Feedback!” Note that including the permafrost feedback would probably make the RCP8.5 scenario in the top figure as much as 1.5°F warmer!
And like the AR4, the AR5 scenarios low-ball future impacts — “Arctic sea ice area is projected to decrease by 28% for September” for the 2016–2035 period vs. 1986–2005. Seriously IPCC, a 28% drop is the scenario your touting? In fact, as we have reported, many experts warn of “Near Ice-Free Arctic In Summer” in a decade if recent ice volume trends continue.
Even so, the uber-conservative AR5 draft makes clear to anyone who reads between the lines that inaction would be suicidal for humanity, with devastating warming and sea level rise that could hit a half a foot a decade by 2100. How precisely does one adapt to that?
Indeed, the report guts the one remaining myth of those who downplay future impacts, that clouds would act as a negative (or weakening) feedback. It finds:
The net radiative feedback due to all cloud types is likely positive.
But the report fails to clearly spell out what the recent science says about inaction — for that you might try “An Illustrated Guide to the Science of Global Warming Impacts” or the recentWorld Bank report, which warned “A 4°C [7°F] World Can, And Must, Be Avoided” To Avert “Devastating” Impacts.
So I can’t see why AR5 would motivate anyone to act more than AR4 and thus I see little real-world value in the entire effort — see my November 2007 post, “Absolute MUST Read IPCC Report: Debate over, further delay fatal, action not costly“! Plus ça change, plus c’est la même chose.
Once again, the authors twist themselves in pretzels to over-hedge every statement with their precise (but inaccurate!) terminology. And so we learn in the draft Summary for Policymakers (SPM):
It is very likely that the Arctic sea ice cover will continue to shrink and thin in the course of the 21st century as global temperature rises.
No, really, it is “very likely” — “> 90% probability” — which I guess means, what, that the IPCC seriously thinks there is an up to 10% chance Arctic sea ice cover will stop shrinking and thinning???
Observations and analysis of drought make clear it is already intensifying in many key regions thanks to global warming — see “NOAA Bombshell: Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts” and “Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse.” But all AR5 can muster up for the probability of future “increases in frequency and/or intensity of drought” is “Likely [> 66% probability] in some regions” — which I guess means the IPCC thinks there is 1 in 3 chance it won’t happen anywhere! How could that be with the kind of warming we will see in the RCP8.5 scenario, which, it must be added is really just business as usual emissions and far from the worst-case?
This failure to warn the public and policymakers echoes the great failing of their 2011 extreme weather report (see “Blockbuster IPCC Chart Hints at Dust-Bowlification, But Report Is Mostly Silent on Warming’s Gravest Threat to Humanity“).
In it most extreme scenario, RCP8.5 — about 936 ppm of CO2 in 2100 (not a worst-case in the real world because of permafrost and other feedbacks) — sea level rise in 2100 is only about 2 feet. That assumes you can figure out what this means: “The contributions from ice sheet dynamical change and anthropogenic land water storage are treated as independent of scenario, since scenario dependence cannot be evaluated on the basis of existing literature, and as having uniform probability distributions, uncorrelated with the magnitude of global climate change.” Clarity ain’t the IPCC’s strong suit.
In any case, most climate scientists expect considerably higher sea level rise, especially if we don’t act. That’s what the recent literature says — see “Sea levels may rise 3 times faster than IPCC estimated, could hit 6 feet by 2100” and “JPL bombshell: Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050.”
Finally, if you read the denier blogs or columnists — and if so, you have no one to blame but yourself — you’ve probably heard something about how the IPCC finds cosmic rays are a major climate driver. In fact, the SPM finds:
Cosmic rays enhance aerosol nucleation and cloud condensation nuclei production in the free troposphere, but there is high confidence that the effect is too weak to have any significant climatic influence during a solar cycle or over the last century.
Below I’m reposting a Skeptical Science piece on the subject.