Contributions of anthropogenic and natural forcing to recent tropopause height changes.
Observations indicate that the height of the tropopause-the boundary between the stratosphere and troposphere-has increased by several hundred meters since 1979. Comparable increases are evident in climate model experiments. The latter show that human-induced changes in ozone and well-mixed greenhouse gases account for approximately 80% of the simulated rise in tropopause height over 1979-1999. Their primary contributions are through cooling of the stratosphere (caused by ozone) and warming of the troposphere (caused by well-mixed greenhouse gases). A model-predicted fingerprint of tropopause height changes is statistically detectable in two different observational ("reanalysis") data sets. This positive detection result allows us to attribute overall tropopause height changes to a combination of anthropogenic and natural external forcings, with the anthropogenic component predominating.
Santer
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BD
Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. santer1@llnl.gov
Wehner
M F
MF
Wigley
T M L
TM
Sausen
R
R
Meehl
G A
GA
Taylor
K E
KE
Ammann
C
C
Arblaster
J
J
Washington
W M
WM
Boyle
J S
JS
Brüggemann
W
W