Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0812721106 (2009)

Credit: JTYLER/ISTOCKPHOTO.COM

The warming, droughts and swollen seas caused by human-generated carbon dioxide are essentially irreversible, say scientists, and will not subside for at least 1,000 years even if emissions cease. It has long been known that a fraction of emitted CO2 lingers in the atmosphere and perpetuates the greenhouse effect for millennia after the bulk of emissions have been absorbed by the ocean.

Now, researchers led by Susan Solomon of the US National Oceanic and Atmospheric Administration in Boulder, Colorado, take a look at how long the effects of that lingering CO2 would last if emissions were abruptly cut off at various atmospheric carbon dioxide concentrations. Using climate projections through 3000 AD, the group estimates that if the atmospheric concentration of CO2 peaked at 600 parts per million, the Mediterranean and western Australia would see centuries of drought, with rainfall down by 13–16 per cent — more than the 10-per-cent drop that caused the 1930s 'dust bowl' in the United States. Slow thermal expansion of the ocean would ultimately raise seas 0.4–1 metres.

Larger responses are possible, as the models don't include ice sheet loss and other important feedbacks. Geoengineering schemes still on the drawing board could offer relief, but were not included in the study.