Long-term evolution of the cold point tropical tropopause: Simulation results and attribution analysis

Abstract

The height, pressure, and temperature of the cold point tropical tropopause are examined in three 140 year simulations of a coupled chemistry climate model. Tropopause height increases approximately steadily in the simulations at a mean rate of 63 ± m/decade (2σ confidence interval). The pressure trend changes near the year 2000 from -1.03 ± 0.30 hPa/decade in the past to -0.55 ± 0.06 hPa/decade for the future. The trend in tropopause temperature changes even more markedly from -0.13 ± 0.07 K/decade in the past to +0.254 ±0.014 K/decade in the future. The tropopause data were fit using regression by terms representing total column ozone, tropical mean sea surface temperatures, and tropical mass upwelling. Tropopause height and pressure closely follow the upwelling term, whereas tropopause temperature is primarily related to sea surface temperature and ozone. The change in tropopause temperature trend near the year 2000 is related to the change in the sign of the ozone trend with the sea surface temperature having an increased role after 2040. A conceptual model is used to estimate tropopause changes. The results confirm the regression analysis in showing the importance of upper tropospheric warming (connected with sea surface temperature) and stratospheric cooling (connected with CO2 and O3). In the past, global warming and ozone depletion have opposite effects on the tropopause temperature, which decreases slightly. For the future simulation, global warming and ozone recovery reinforce which increases the tropopause temperature. In particular, future tropopause change is found not to be an indicator of climate change alone. Copyright 2008 by the American Geophysical Union.