On March 12, researchers reported that carbon dioxide concentrations in the atmosphere moved above 400 parts-per-million en route to a springtime peak. During spring, trees and other plants begin to draw down CO2 levels to fuel leaf growth. But this is the second time in as many years that levels have risen above 400 ppm, a mark never before experienced in the entire time our species has walked the Earth.
So the important question is: exactly how sensitive is the Earth's climate to these ever-increasing greenhouse gases? Will warming happen gradually or quickly, and to what extent? Even more importantly, how can we find out without the potentially catastrophic experiment we are presently running?
A recent study suggests that other greenhouse gases may be the key to answering this question. Specifically soot-like air pollution and ozone. Taking into account the unique characteristics of this localized air pollution suggests that the climate is "very unlikely" to be insensitive. The research appears in the journal Nature Climate Change. [Drew T. Shindell, Inhomogeneous forcing and transient climate sensitivity]
That means climate change with an increase of more than a degree Celsius compared with the last century is very likely already. It's going to take cutting out most further greenhouse gas pollution to restrain further global warming.
—David Biello
[Scientific American is part of the Nature Publishing Group.]
