The importance of atmospheric chemistry in the calculation of radiative forcing on the climate system

Abstract

An interactive two‐dimensional model of the troposphere, stratosphere, and mesosphere, in which dynamics, radiation, and chemistry are treated interactively, is used to investigate the anthropogenic changes in the steady state chemical composition of the atmosphere since preindustrial times and to assess the associated changes in radiative forcing on climate. The perturbations in the atmospheric oxidation capacity due to anthropogenic emissions of source gases are found to be significant. In the troposphere, an ozone increase of 80–120% at northern midlatitudes and a global decrease of 10–20% in the OH concentration since the preindustrial period are calculated. In the polar lower stratosphere of the southern hemisphere, an ozone depletion since preindustrial times reaching more than 60% during spring is calculated as a result of rapid catalytical destruction of ozone by chlorine radicals in the presence of polar stratospheric clouds. Particular attention is given to the induced changes in radiative forcing. These results stress the potentially important role of chemical feedbacks on climate and indicate that the direct forcing associated with increasing concentrations of greenhouse gases is enhanced by about 30% when these feedbacks are taken into account. On a global average basis, the greenhouse effect of tropospheric ozone represents approximately 17% of the total radiative perturbation. This forcing is characterized by a strong latitudinal dependence, peaking at midlatitudes in the northern hemisphere. The importance of indirect climate forcings by stratospheric ozone (including local cooling of the stratosphere) is confirmed. It is found that the net (solar + infrared) indirect effect of stratospheric ozone changes is to increase the chlorofluorocarbon direct radiative forcing. On the other hand, the change in the longwave forcing associated with water vapor increase in the stratosphere appears to play a minor role.

Photolysis imprint in the nitrate stable isotope signal in snow and atmosphere of East Antarctica and implications for reactive nitrogen cycling

“…e after Hudson et al (2002). f Based on a dry deposition velocity of 0.5 cm s −1 (Hauglustaine et al, 1994) and a mean accumulation rate of 3.1 g cm −2 yr −1 (Legrand and Delmas, 1988;Röthlisberger et al, 2000).…”

Impact of climate change on tropospheric ozone and its global budgets

“…Numerous studies of the evolution of tropospheric O 3 changes since preindustrial times and the associated radiative forcings have been carried out using various chemical transport or climate models (e.g., Hauglustaine et al, 1994;Forster et al, 1996;Roelofs et al, 1997;Berntsen et al, 2000;Brasseur et al, 1998;Stevenson et al, 1998a;Mickley et al, 1999;Hauglustaine and Brasseur, 2001;Grenfell et al, 2001). However there is often significant difference between models in their predictions of ozone change, (see, e.g.…”

Global change: state of the science

“…Changes in tropospheric ozone above the boundary layer, which contains much of the ozone from local and regional air pollution, can also a ect climate (Lacis et al, 1990). Ozone changes in this region are much more uncertain than those in the stratosphere, although calculations indicate that an increase in ozone over recent decades, as suggested by some measurements, should add to the warming e ect in radiative forcing from greenhouse gases (Wang et al, 1993;Hauglustaine et al, 1994). Estimates of the change in radiative forcing since the 1700s for tropospheric ozone range from 0.2 to 0.6 Wm À2 (IPCC, 1995).…”