Observational satellite data and a computer model have predicted response to human influence have a common latitude/altitude pattern of atmospheric temperature change.
The key features of this pattern are global-scale tropospheric warming and stratospheric cooling over the 34-year satellite temperature record.
The troposphere is the lowest portion of Earth's atmosphere. The stratosphere lies above the troposphere.
A new report compared multiple satellite records of atmospheric temperature change with results from a large, multi-model archive of simulations. Fingerprint information has proved particularly useful in separating human, solar and volcanic influences on climate.
"Human activity has very different effects on the temperature of the upper and lower atmosphere, and a very different fingerprint from purely natural influences," said Benjamin Santer of Lawrence Livermore National Lab, the lead researcher on the paper. "Our results provide clear evidence for a discernible human influence on the thermal structure of the atmosphere. Current climate models are highly unlikely to produce this distinctive signal pattern by internal variability alone, or in response to naturally forced changes in solar output and volcanic aerosol loadings."
Natural internal fluctuations in climate are generated by complex interactions of the coupled atmosphere-ocean system, such as the well-known El Niño/Southern Oscillation. External influences include human-caused changes in well-mixed greenhouse gases, stratospheric ozone and other radiative forcing agents, as well as purely natural fluctuations in solar irradiance and volcanic aerosols. Each of these external influences has a unique "fingerprint" in the detailed latitude/altitude pattern of atmospheric temperature change.'
"The pattern of temperature change that has been observed vertically in the atmosphere, from ground level to the stratosphere, fits with what is expected from human-caused increases in greenhouse gases. The observed pattern conflicts with what would be expected from an alternative explanation, such as fluctuations in the sun's output," Santer said.
Co-author of the paper Céline Bonfils noted that major volcanic eruptions also can profoundly disturb the vertical structure of atmospheric temperature. "During the recovery from such eruptions, tropospheric warming and stratospheric cooling also occur" Bonfils said. "But in contrast to volcanic influences, human-caused atmospheric temperature changes affect all latitudes and last longer. This suggests that the recent changes in temperature are not simply a recovery from past volcanic events."
Benjamin D. Santer, Jeffrey F. Painter, Céline Bonfils, Carl A. Mears, Susan Solomon, Tom M. L. Wigley, Peter J. Gleckler, Gavin A. Schmidt, Charles Doutriaux, Nathan P. Gillett, Karl E. Taylor, Peter W. Thorne, and Frank J. Wentz , 'Human and natural influences on the changing thermal structure of the atmosphere', PNAS September 16, 2013, doi:10.1073/pnas.1305332110