The tropopause is the boundary between troposphere (which is based at the earth's surface and has temperature that decreases with height) and the stratosphere (which is a stable region of very low levels of vertical mixing above the troposphere). The tropopause is higher than the global average in warm regions (e.g., tropics) and lower in cold regions (e.g., polar regions). If the atmosphere is warming due to climate change, then we might expect the height of the tropopause to increase. Santer et al (2003) have reviewed data on tropopause heights and find that, indeed, it has increased over the period 1979-1999 by about 200 m. They use a global climate model to simulate this process and examine the impact of changes in greenhouse gases and ozone. Ozone absorbs UV radiation in the stratosphere, which provides heat to balance the heat loss due to infrared radiation. Reduced ozone levels means reduced heating and hence rise of the tropopause. Increased concentration greenhouse gases in the troposphere leads to increased absorption of infrared radiation throughout this region and also contributes to a rise in the tropopause. According to the global climate model used by Santer el al, (2003) these two factors can explain 80% of the rise in the tropopause height over the 20-year period they examined. More discussion on this research is supplied by Hoskins (2003).
Reference
Hoskins, B. J., 2003: Climate change at cruising altitude. Science 301, 469-470.
Santer, B. D. et al, 2003: Contributions of anthropogenic and natural forcing to recent tropopause height changes. Science 301, 479-483.
