Atmospheric Chemistry and Climate in the Anthropocene

Humans are changing critical environmental conditions in many ways. Here, the important changes in atmospheric chemistry and climate are discussed. The most dramatic examples of major human impacts are the increase of the “greenhouse” gases, especially carbon dioxide (CO2), in the atmosphere and the unpredicted breakdown of much of the ozone in the lower stratosphere over Antarctica during the months of September to November, caused by the emissions of chlorofluorocarbons (CFCs). Other, more regional but ubiquitous examples include photochemical smog and acid rain.

Industrial activities are not alone in causing air pollution and in changing the chemical composition of the atmosphere. Biomass burning, which takes place largely in the developing world, also contributes in major ways.

In the future, climate warming due to CO2 emissions will continue to increase over present levels and pose a major problem for humankind. Current radiative forcing by “greenhouse gases” can, to a substantial degree (up to half), be dampened by increased backscattering of solar radiation, either directly by aerosol particles or indirectly through their influence on cloud albedo, or also by cloud feedbacks independent of anthropogenic aerosols. Cloud and hydrological cycle feedbacks provide major challenges. It is unlikely and undesirable that aerosol emissions will continue to increase, as greater emphasis will be placed on air quality, also in the developing world. However, due to its long atmospheric lifetime and expected growth in global emissions, CO2 will continue to accumulate, exacerbating climate warming and related problems in the future. Drastic measures are thus needed at the international level to reduce the emissions, in particular, of CO2 through energy savings, alternative energy sources, and sequestration.