Important new research led by NOAA scientists, “Irreversible climate change because of carbon dioxide emissions,” finds:
… the climate change that is taking place because of increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop … Among illustrative irreversible impacts that should be expected if atmospheric carbon dioxide concentrations increase from current levels near 385 parts per million by volume (ppmv) to a peak of 450-600 ppmv over the coming century are irreversible dry-season rainfall reductions in several regions comparable to those of the “dust bowl” era and inexorable sea level rise.
I guess this is what President Obama meant when he warned today of “irreversible catastrophe” from climate change. The NOAA press release is here. An excellent video interview of the lead author is here.
The Proceedings of the National Academies of Science paper gives the lie to the notion that it is a moral choice not to do everything humanly possible to prevent this tragedy, a lie to the notion that we can “adapt” to climate change, unless by “adapt” you mean “force the next 50 generations to endure endless misery because we were too damn greedy to give up 0.1 percent of our GDP each year” (see, for instance, McKinsey: Stabilizing at 450 ppm has a net cost near zero or the 2007 IPCC report).
The most important finding concerns the irreversible precipitation changes we will be forcing on the next 50 generations in the U.S. Southwest, Southeast Asia, Eastern South America, Western Australia, Southern Europe, Southern Africa, and northern Africa.
Here is the key figure (click to enlarge):
Figure: Best estimate of expected irreversible dry-season precipitation changes, as a function of the peak carbon dioxide concentration during the 21st century. The quasi-equilibrium CO2 concentrations shown correspond to 40 percent remaining in the long-term as discussed in the text. The yellow box indicates the range of precipitation change observed during typical major regional droughts such as the “dust bowl” in North America (except, of course, this Dust Bowl lasts 1,000 years, not 10 to 20, which is what some people might call a desert).
On our current emissions path, we are headed toward 1,000 ppm by century’s end, as a close reading of the IPCC report makes clear (see my 2008 recent Nature online article). That would put essentially every at risk region into conditions worse than the Dust Bowl for a long, long, long time. Clearly we must peak no higher than 450 ppm.
Discount rates used in some estimates of economic trade-offs assume that more efficient climate mitigation can occur in a future richer world, but neglect the irreversibility shown here.
This is also an important admonition to reporters who cover the climate economics debate (see “How the press bungles its coverage of climate economics“).
The lead author, NOAA senior scientist Susan Solomon, spoke to reporters this morning:
Asked whether current efforts by some scientists and engineers to invent ways to suck excess CO2 straight out of the air would mean global warming could in fact be reversed after all, she agreed it would, “if by some miracle” such engineering feats could ever be realized.
Otherwise, she said, her study was only further proof of the urgency of the need for humanity to drastically reduce its greenhouse emissions worldwide.
Heck, I say, let’s do some geo-engineering research, but let’s not be deluded into thinking that pursuing research is the same thing as having any reason to believe that research will lead to anything practical or affordable — or any more successful than the billions we have flushed down the toilet trying to build a practical and affordable hydrogen car.
If geo-engineering CO2 out of the air is plausible and affordable at a large scale, it is only after serious mitigation, to go from, say, a brief peak at 450 ppm, back to 400 ppm or lower. Going from 1,000 ppm down to below 400 ppm is not only a staggering task to imagine — where the heck would you put the hundreds of billions of tons of carbon? — but it would also be too late to save the ocean from becoming one large, acidic dead zone, and, in any case, we probably would have crossed carbon cycle tipping points that unleash the methane in the peatlands and permafrost.
Bottom line: A few decades of prevention is worth 1,000 years of
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