Global Atmospheric-Biospheric Chemistry

Abstract

International concerns about the possibility of detrimental future climate change rest to a significant degree on the documented fact that the atmospheric levels of a number of long-lived greenhouse gases are steadily rising. The underlying causes for the currently observed changes in atmospheric composition involve both natural physical, chemical and biological processes and vital human activities like energy and food production. There is also clear evidence for major changes in atmospheric composition over the last 160,000 years contained in ice cores. The ice core data show us that atmospheric changes can be driven by natural processes alone so the current human processes need to be understood in terms of their perturbations to the natural biogeochemical cycles. Human activity is certainly a major contributor to the positive atmospheric trends of CO2 (0.4% per year), CH4 (1.2 down to 0.3% per year), and N2O (0.25% per year) in recent decades. Humans are in addition the sole contributor to the observed positive CF2Cl2 and CFCl3 trends (4.0% and 3.8% per year respectively in 1978-1988, 2.6% and 3.2% per year respectively in 1989-1991) and probably also for the observed negative trends in stratospheric O3 (0.2% to 3% per year depending on latitude). Tropospheric O3 appears to have increased at least in northern hemisphere midlatitudes over the last century and there are reasons to expect such an increase based on combustion-derived emissions. Similarly, SO2 levels, while controlled in some industrially developed countries, are increasing in several industrially developing regions due particularly to increased coal combustion. All of these trends are important to radiative forcing of climate change: positive trends for CO2, CH4, N2 O, CFCl3, CF2Cl2, and tropospheric ozone produce a positive (warming) force while negative trends for stratospheric ozone and positive trends for SO2 (and thus for the derived reflective sulfate aerosols) produce a negative (cooling) force. Biological processes in terrestrial ecosystems (cultivated or natural) play major roles in the budgets of CO2, CH4 and N2O while marine biology plays a significant role in controlling remote marine atmospheric SO2 levels and the flux of CO2 between atmosphere and ocean. The International Global Atmospheric Chemistry (IGAC) Project of the International Geosphere-Biosphere Program (IGBP) is underway and devoted to understanding the complex coupled atmospheric and biospheric chemistry leading to currently observed changes in atmospheric composition and to improving our capability to predict future changes in atmospheric gaseous and paniculate composition.KeywordsMethane EmissionBiomass BurningStratospheric OzoneCloud Condensation NucleusAtmospheric CompositionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.