Arctic hurricanes, also known as polar lows, are explosive storms that develop and die over a few days. They form when cold air from the Arctic flows south over warmer water: the air takes up heat, expands and rises, generating convection currents that sometimes snowball into storms.
Zahn and his colleague Hans von Storch, of the Meteorological Institute at Hamburg University, used a global climate model to project the impact of three scenarios on temperature, humidity and other variables in 2100. They then fed this data into a regional model to assess how polar lows may respond.
Assuming that greenhouse gas emissions rise rapidly in the future, the frequency of Arctic hurricanes could fall from an average of 36 per winter to about 17 by 2100, the model suggests. If emissions rise more slowly the number of hurricanes could fall to 23 per winter.
Polar lows are less likely to form in the future because climate change will warm up the air in the north Atlantic faster than it warms up the ocean, reducing the thermal difference and reducing the risk of convection currents forming.
The Arctic is of great interest to oil and gas companies, but Doug Parr, chief scientist at Greenpeace UK, says many are concerned that extreme weather as well as icebergs could damage rigs and trigger oil spills. However he warns industry against interpreting Zahn’s results as a signal that the region is safe to exploit.
“As we have seen from BP in the Gulf of Mexico, there are plenty of hazards associated with drilling for oil and gas that have nothing to do with the weather,” says Parr. “Even if the frequency of hurricanes declines, we would be bonkers to go into such a fragile ecosystem and risk sacrificing it just to obtain more oil.”
Erik Kolstad at the Bjerknes Centre for Climate Research in Bergen, Norway, adds that while polar lows may be reduced in some Arctic regions, they would only move onto others where sea ice has retreated to form new ocean.
“These regions include the Barents Sea, where the Russians are exploring for gas and oil, the Northern Sea Route, where shipping companies hope to be able to travel from Asia to Europe, and in the Beaufort Sea, where the Canadians are exploring for oil and gas,” says Kolstad.
Fewer polar storms could also mean less extreme weather in the UK, says Suzanne Gray at the Mesoscale Group at the University of Reading, who was not part of the research team. “Polar lows occasionally lead to heavy snowfall even over England. Motorways get blocked and people have to sleep in their cars overnight. So perhaps we won’t be seeing so many of them in the future.”