Climate change

Over the past 50 years Earth's climate has become warmer and is projected to increase by 2-5 degrees until the end of the 21st century. Climate models forced by increased greenhouse gas emissions suggest that under global warming the Hadley cells, jet streams and midlatitude storm tracks will shift poleward. While the poleward shift is a robust response across most models, there is currently no consensus on what the underlying dynamical mechanism is. We use numerical modeling ranging from idealized models to full GCMs study the consequence of global warming, with focus on the extratropical climate and large scale circulation. In a series of papers we have shown that in addition to a poleward shift in the genesis latitude of the storms, associated with the shift in baroclinicity, the latitudinal displacement of cyclonic storms increases under global warming. This is achieved by applying a storm-tracking algorithm to an ensemble of CMIP5 models. The increased latitudinal propagation in a warmer climate is shown to be a result of stronger upper-level winds and increased atmospheric water vapor. These changes in the propagation characteristics of the storms can have a significant impact on midlatitude climate. Another key issue is the fact that as a result of global warming upper level temperature gradients are expected to increase while lower-level temperature gradients are expected to decrease. This, in addition to the variation in static stability strongly affect baroclinicity in the atmosphere. Understanding how baroclinicity variation will affect the eddy fields is a key direction of research.

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