Human Activity Directly Affects Vertical Structure of Atmospheric Temperature: A Study

The vertical structure of atmospheric temperature is directly affected by human activity, a new published in the Proceedings of the National Academy of Sciences study suggests.

Conducted by researchers from a wide range of scientific institutions, the study compares multiple satellite records of changes in atmospheric temperature with results with "a large, multi-model archive of simulations," according to the press release detailing the report.

From this data the researchers detected several patterns, including a 34-year period of warming in the lowest portion of the Earth's atmosphere in conjunction with cooling in the layer right above it. 

"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," said Benjamin Santer, the study's lead researchers and a climate scientist from the Lawrence Livermore National Laboratory."

More than simply monitoring trends, however, the researchers analyzed the information in order to tease out their specific causes.

"Human activity has very different effects on the temperature of the upper and lower atmosphere, and a very different fingerprint from purely natural influences," Santer said. "Our results provide clear evidence for a discernible human influence on the thermal structure of the atmosphere."

Deciphering this fingerprint was key to differentiating human-caused temperature change with that caused by natural causes, each of which carry a fingerprint of their own.

"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," Santer explained. "The observed pattern conflicts with what would be expected from an alternative explanation, such as fluctuations in the sun's output."

Among those naturally-occurring phenomenon most disturptive to the vertical structure of atmospheric temperature are volcanoes. However, as co-author and LLNL researchers Celine Bnofils notes, "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."