The role of the atmospheric energy transport in recent Arctic climate change
Supported by the Research Council of Norway
Does changes in the atmospheric circulation lead to Arctic warming and melting of the Greenland ice sheet?
The Arctic shows some of the world’s most significant signs of climate change. These signs include a strong negative trend in summer sea-ice cover, and a warming which is three times larger than the global average.
A large concern for humanity is that the climate change in the polar regions will lead to significant melting of the ice sheets and glaciers and hereby to rising of the sea level. Through the history we have built cities and infrastructure at low altitude close to the sea; human habitation at many of these locations will be challenged given a sea-level rise of a few meters. The melting of the Greenland ice sheet has in recent decades increased to the extent that this ice sheet is now one of the major contributors to sea-level rise.
The atmospheric circulation plays a crucial role for the Arctic climate. For instance, in the the high Arctic where solar radiation is absent in the winter months, the temperature would have been far below -100 °C during this season, had it not been for the atmospheric circulation bringing warm air from the south to these northerly latitudes. In addition the atmospheric circulation plays a key role for the melting of the Greenland ice sheet, since it can bring warm air in over the ice leading to ice melt, or humid air leading to more precipitation and ice growth.
There has been little emphasis on the role of the atmospheric circulation in recent Arctic climate change and in the recent strong melt of the Greenland ice sheet. Based on a combination of analysis of observations, statistical methods, and modelling this project will approach these questions.
Some project results of 2019:
Science work within the project reveals that humid winds cause considerable more Arctic warming than previously known. As the climate changes due to enhanced concentrations of greenhouse gases in the atmosphere, more humid air is transported northward contributing to warming and melting of sea ice in the Arctic. The humid air increases the cloudiness over the Arctic, and both the clouds and the humid air enhance the greenhouse effect over the Arctic inducing more absorption and re-emission of longwave radiation back to the surface hereby leading to increased surface warming (Gaversen and Langen, J. Climate, 2019).
Within the project, development is conducted of methods to estimate contributions to the atmospheric energy transport due to various atmospheric phenomena such as cyclones and what is known as planetary waves. A study within the project shows that planetary waves accomplish by far the largest part of the atmospheric energy transport in the mid latitudes, especially when it comes to extreme cases where the energy transport is in particularly strong. This study increases our understanding of the physical processes underlying the atmospheric energy transport (Lembo et al., Geophys. Res. Lett., 2019).
Graversen R. G. and P. L. Langen: On the Role of the Atomspheric Energy Transport in 2xCO2-Induced Polar Amplification in CESM1. J. Climate, 32, 3941-3956, 2019
Lembo V., G. Messori, R. Graversen, and V. Lucarini: Spectral Decomposition and Extremes of Atmospheric Meridional Energy Transport in the Northern Hemisphere Midlatitudes, Geophys. Res. Lett., 46, 7600-7613, 2019