Greenhouse gas growth rates

We posit that feasible reversal of the growth of atmospheric CH 4 and other trace gases would provide a vital contribution toward averting dangerous anthropogenic interference with global climate. Such trace gas reductions may allow stabilization of atmospheric CO 2 at an achievable level of anthropogenic CO 2 emissions, even if the added global warming constituting dangerous anthropogenic interference is as small as 1°C. A 1°C limit on global warming, with canonical climate sensitivity, requires peak CO 2 ≈ 440 ppm if further non-CO 2 forcing is +0.5 W/m 2 , but peak CO 2 ≈ 520 ppm if further non-CO 2 forcing is -0.5 W/m 2 . The practical result is that a decline of non-CO 2 forcings allows climate forcing to be stabilized with a significantly higher transient level of CO 2 emissions. Increased “natural” emissions of CO 2 , N 2 O, and CH 4 are expected in response to global warming. These emissions, an indirect effect of all climate forcings, are small compared with human-made climate forcing and occur on a time scale of a few centuries, but they tend to aggravate the task of stabilizing atmospheric composition.