Department of Earth System Science

Anthropogenic emissions of short-lived, chemically reactive gases, such as NO_x and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O₃, CH₄ and the HFCs. This study uses the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NO_x and CO emissions into (i) short-lived modes involving predominantly tropospheric O₃ and (ii) the long-lived mode involving a global coupled CH₄-CO-O₃perturbation. Combining these two classes of greenhouse perturbations—large, short-lived, regional O₃ increases and smaller, long-lived, global decreases in CH₄ and O₃—we find that most types of anthropogenic NO_x emissions lead to a negative radiative forcing and an overall cooling of the earth.