Geophys. Res. Lett. http://doi.org/9q6 (2015)

The increase in global surface temperatures due to climate change is well known. Another, less-explored consequence is thermal expansion of the atmosphere, which can trigger circulation changes that also affect regional climate.

Nikolaos Christidis and Peter A. Stott, from the Met Office Hadley Centre, UK, investigate recent changes (from 1979 onwards) in the temperature and circulation of the lower atmosphere. Using satellite and model data, they determine trends in geopotential height, a measure of the height necessary to reach a given pressure in the atmosphere (in this case, 500 millibar). They then use statistical analysis to attribute these changes to either natural or anthropogenic causes.

Overall, they find a significant increase in this geopotential height owing to human influence. However, this trend is spatially variable. For example, in the Northern Hemisphere the increase is stronger over the poles relative to the mid-latitude regions. This could affect the position of the North Atlantic jet stream, which regulates European climate.

This suggests that warming of the lower atmosphere may lead to circulation changes. But this effect is weak and needs to be investigated further to determine which changes are robust.