Polar amplification

Polar amplification is the phenomenon that any change in the net radiation balance (for example greenhouse intensification) tends to produce a larger change in temperature near the poles than the planetary average. On a planet with an atmosphere that can restrict longwave radiation to space (a greenhouse effect), surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict. Where the atmosphere or an extensive ocean is able to convect heat polewards, the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict.  

In the extreme, the planet Venus is thought to have experienced a very large increase in greenhouse effect over its lifetime, so much so that its poles have warmed sufficiently to render its surface temperature effectively isothermal (no difference between poles and equator).   On Earth, water vapor and trace gasses provide a lesser greenhouse effect, and the atmosphere and extensive oceans provide efficient poleward heat transport. Both palaeoclimate changes and recent global warming changes have exhibited strong polar amplification, as described below.

Feedbacks associated with sea ice and snow cover are widely cited as the main cause of recent terrestrial polar amplification. However, amplification is also observed in model worlds with no ice or snow. It appears to arise both from a (possibly transient) intensification of poleward heat transport and more directly from changes in the local net radiation balance (an overall decrease in outward radiation will produce a larger relative increase in net radiation near the poles than near the equator).

Some examples of climate system feedbacks thought to contribute to recent polar amplification include the reduction of snow cover and sea ice, changes in atmospheric and ocean circulation, the presence of anthropogenic soot in the Arctic environment, and increases in cloud cover and water vapor. Most studies connect sea ice changes to polar amplification. Some models of modern climate exhibit Arctic amplification without changes in snow and ice cover. The individual processes contributing to polar warming are critical to understanding climate sensitivity.

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