Warming Arctic may be influencing hurricanes

IN THE wake of devastating back-to-back hurricanes Harvey and Irma, climate scientists are discussing the link between climate change and extreme storms with renewed vigour.

They agree on some points – for instance, many researchers believe a warmer atmosphere will produce hurricanes with higher rainfall.

But other theories about climate change and extreme weather are more controversial.

Recent events have once again raised one of the biggest debates in climate science – whether the warming Arctic might be influencing the tracks of hurricanes and other weather patterns.

Some climate scientists suggest that warming in the Arctic could affect the flow of large-scale atmospheric currents – notably the jet stream, a huge, wavy air current that flows from west to east around the world and has a major influence on global weather patterns.

Some scientists suggest the theory could help explain the remarkable trajectory of Hurricane Sandy, which crashed into the New Jersey coast in 2012. And now they suggest that the unusual behaviour of Hurricane Harvey – which stalled over Texas, dumping record amounts of rain – could be related to Arctic-driven changes in the jet stream as well.

In a Facebook post, published in the aftermath of Harvey’s landfall, climate scientist Michael Mann of Pennsylvania State University noted that Harvey’s devastating stalling behaviour had been made possible by weak prevailing winds, which were associated with “a greatly expanded subtropical high pressure system over much of the US, with the jet stream pushed well to the north”. While it was a “tenuous” idea, the phenomenon of weather patterns becoming locked in place for unusually long periods “appears to be favoured by humancaused climate change”.

Climatologist Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, made a similar observation, noting that the effects of Arctic warming could slow atmospheric circulation, allowing weather systems to “move less and stay longer in a given location – which can enhance the impacts of rainfall extremes”.

This is not to say that Harvey’s behaviour was caused by Arctic warming alone – it’s difficult to pin individual weather events on any single factor, and Mann cautioned that it couldn’t be said that Arctic warming was responsible for Harvey. But some scientists suggest that this type of event, in general, might be more likely to occur as a result of changes in the Arctic.

Other experts believe there’s not enough evidence for it to be credible. “The jury is out on that,” said Tapio Schneider, a climate scientist at California Institute of Technology, referring specifically to the conditions in Harvey. Climate modelling results are ambiguous.”

– Washington Post

THE JURY IS OUT, CLIMATE MODELLING RESULTS ARE AMBIGUOUS