The Contribution From Emissions of Different Gases to the Enhanced Greenhouse Effect

The main purpose of this paper is to compare the different contributions, that mankind has made to perturbing the atmosphere`s radiative balance. We have, and will continue to perturb both the balance of outgoing long-wave radiation and the balance of incoming short-wave radiation. Human activities since preindustrial times have caused a substantial enhancement of the greenhouse effect, a process involving the absorption of outgoing long-wave radiation which leads to a warming of the lower atmosphere. Because the atmosphere`s short-wave radiative balance is affected by the presence of small particles (aerosols) produced by the oxidation of sulphur compounds, anthropogenic emissions of sulphur dioxide (SO{sub 2}) have also caused a perturbation of the overall balance. The greenhouse gases we will consider are, in order of importance: carbon dioxide (CO{sub 2}), Methane (CH{sub 4}), nitrous oxide (N{sub 2}O) and the halocarbons. We use observed and model-based concentration data together with the most recent information relating concentrations to radiative forcing to estimate the individual contributions of the different gases to the changing radiative balance of the atmosphere. We also estimate the ranges of uncertainty in each of these estimates. We base all results on the 1992 IPCC emissions scenarios IS92a-f. We begin with amore » summary of 1990 conditions, then consider each gas separately (but lumping the halocarbons into a single group), to compare their relative importance.« less