Use of changes in tropopause height to detect human influences on climate

The height of the global-mean tropopause shows a steady increase since 1979 in re-analyses of numerical weather forecasts. This is in agreement with results from a climate model driven by natural and anthropogenic forcings. Superimposed on the multi-decadal overall trends in both simulations and re-analyses are higher-frequency fluctuations (with periods of few years) related to explosive volcanic eruptions. Global-mean tropopause height has the desirable property of acting as a natural filter, removing much of the ENSO variability that hampers the interpretation of tropospheric and surface temperature changes. In model simulations with anthropogenic forcings, changes in tropopause height can be detected roughly 20 years earlier than changes in surface temperature.