title: Contributions of anthropogenic and natural forcing to recent tropopause height changes.
abstract: 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.
authors.affiliation: Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. santer1@llnl.gov
authors.forename: B D
authors.initials: BD
authors.lastname: Santer
authors.forename: M F
authors.initials: MF
authors.lastname: Wehner
authors.forename: T M L
authors.initials: TM
authors.lastname: Wigley
authors.forename: R
authors.initials: R
authors.lastname: Sausen
authors.forename: G A
authors.initials: GA
authors.lastname: Meehl
authors.forename: K E
authors.initials: KE
authors.lastname: Taylor
authors.forename: C
authors.initials: C
authors.lastname: Ammann
authors.forename: J
authors.initials: J
authors.lastname: Arblaster
authors.forename: W M
authors.initials: WM
authors.lastname: Washington
authors.forename: J S
authors.initials: JS
authors.lastname: Boyle
authors.forename: W
authors.initials: W
authors.lastname: Brüggemann