Atmospheric Composition Change: Climate–Chemistry Interactions

The coupling between climate change and atmospheric composition results from the basic structure of the Earth atmosphere climate system, and the fundamental processes within it. The composition of the atmosphere is determined by natural and human-related emissions, and the energy that flows into, out of, and within the atmosphere. Atmospheric composition influences climate by regulating the radiation budget. Potentially significant contributions to the climate impact are provided by compounds such as CO2, CH4, O3, particles, and cirrus clouds. For the chemically active gases, processes in the atmosphere are important, with large spatial and temporal variations. The climate–chemistry interactions are therefore characterized by significant regional differences with regions such as South East Asia being a future key region due to significant increases in energy use and pollution emission. Likewise, ship and air traffic represent important sectors because of significant increases in emissions in recent years. The relative contributions to the emissions from various sectors are expected to change significantly over the next few decades due to differences in mitigation options and costs.