The weather in Eurasia, Australia, and North and South America is heavily influenced by the strength and position of extra-tropical storm tracks. Climate change is altering the temperature gradient between the warm equator and the colder polar regions; this is expected to affect the position and strength of mid-latitude storms. But exactly how will it alter those storms? Using the Coupled Model Intercomparison Project (CMIP5) ensemble, Jascha Lehmann from Germany’s Potsdam Institute for Climate Impact Research and colleagues rolled climate forward to 2100 and looked at the change in storm tracks under a high carbon-dioxide-emissions scenario.

The team found a distinct tale of two hemispheres. Averaged over the northern mid-latitudes, future mean storm track activity showed little change during the winter, but significant decreases during the summer. Meanwhile, in the southern hemisphere storm activity intensified during winter but showed little change during the summer. “In both cases this leads to an amplified seasonal signal,” said Lehmann, whose findings are published in Environmental Research Letters (ERL).

The differing response between the hemispheres is partly due to the arrangement of continents and ocean, with the northern hemisphere's more continent-heavy distribution making for more chaotic air-flow patterns.

People in both hemispheres could be in for some unpleasant weather. “Storms bring moist and cool air from the oceans to the continents and thus a weakening of storm tracks during northern-hemisphere summer could possibly lead to more prolonged heat waves or droughts in the mid-latitudes across Europe and North America,” said Lehmann. Meanwhile, inhabitants of Australia, New Zealand, South America and South Africa, at mid-latitudes in the southern hemisphere, might experience stronger and more frequent winter storms, leading to a greater likelihood of flooding.

For the residents of the Somerset Levels, UK, an area particularly badly hit by flooding last winter, it may come as a relief to hear that such weather is not expected to become the norm. However, Lehmann and his colleagues caution that there will be regional exceptions where the weather patterns don't follow the average northern-hemisphere pattern. And early regional indications suggest that Western Europe could see an increase in winter storm track activity.

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