Atmospheric ozone and climate change

摘要

Ozone concentrations in the troposphere have increased significantly since pre-industrial time due to emission of ozone precursors (NOx, CO, CH_4, NMHC). Using a combination of observations and model studies it has been estimated that the global average value has increased with approximately 30 % to its present global average value of approximately 50 ppb. During the last two decades ozone growth in the troposphere has slowed down, and he current trend is unclear. Future increases in ozone are critically depending on the emission scenarios used. Adopting the IPCC SRES high emission scenario (A2), model studies give a significant growth in the ozone burden. Over the next 100 years average tropospheric concentrations could increase by more than 50 %. Estimates of radiative forcing give tropospheric ozone as the third most important man induced greenhouse gas (after CO_2 and CH_4). Estimates of the radiative forcing from tropospheric ozone since pre-industrial time are of the order 0.3 to 0.4 W/m~2. The observed changes (reductions) in stratospheric ozone are estimated to give a noticeable negative radiative forcing. The growth in ozone during this century could lead to a radiative forcing up to 0.6 W/m~2. This would be a significant contribution to the overall radiative forcing. The few studies performed up to now of the climate-chemistry interaction indicate a two way effect: Climate changes is likely to substantially affect the ozone chemistry, and changes in ozone chemistry affect the forcing of the climate system.