Vinnikov et al. (1996) Vinnikov, Konstantin Ya., Alan Robock, Ronald J. Stouffer and Syukuro Manabe, 1996: Vertical patterns of free and forced climate variations. Geophys. Res. Lett., 23, 1801-1804.


Observations of the vertical structure of atmospheric temperature changes over the past three decades show that while the global-average lower atmosphere has warmed, the upper troposphere and lower stratosphere have cooled. While these changes resemble model calculations of the expected changes due to observed anthropogenic increases of greenhouse gases, decreases of lower stratospheric ozone, and increases of tropospheric aerosols, the changes may also have been caused by natural unforced internal fluctuations of the climate system. Here we use the results of a 1000-year simulation from a mathematical model of the coupled ocean-atmosphere-land system performed without any changes in external forcing, so that we may consider its variations as a surrogate for free, internally-generated, natural fluctuations of the climate system. When the global mean surface air temperature is warm in the model, the lower troposphere, upper troposphere and lower stratosphere are also warm over most of the Earth, in contrast to the observations of the last three decades and to model simulations of the forced climate response due to increased greenhouse gases. The observed temperature change of the past three decades is therefore unlikely to have been caused by natural internal variations of the climate system, thereby strengthening the argument that these changes can be attributed to anthropogenic activities.

Prepared by Alan Robock ( ) - Last updated on April 21, 1999