The consensus of climate scientists is increasingly that super storms will become more frequent. According to a recent special report by the Intergovernmental panel on climate change: “The average tropical cyclone maximum wind speed is likely to increase, but the global frequency of tropical cyclones is likely to decrease or remain unchanged.”
In September, the IPCC’s fifth assessment stated, more cautiously: “Time series of cyclone indices such as power dissipation, an aggregate compound of tropical cyclone frequency, duration, and intensity that measures total wind energy by tropical cyclones, show upward trends in the North Atlantic and weaker upward trends in the western North Pacific since the late 1970s, but interpretation of longer-term trends is again constrained by data quality concerns.”
In other words, the best science says there is some evidence that storm intensity has already increased, at least in the North Atlantic, but there’s not enough data to say categorically that any particular weather event can be linked to climate change.
But the science is moving on quickly and it is now possible, with new modeling methods, to quantify and attribute the changed odds of any given event happening. “Because of the random nature of weather, it had been assumed until recently that no single event can be attributed to climate change. However, with new research methods and better quality data, scientists are increasingly able to connect the dots between extreme weather events and climate change,” says James Bradbury, formerly a researcher with the World Resources Institute in Washington and now with the US department of energy.
“For example, one can quantify the odds of a typical heatwave happening and estimate how much a warmer world would load the dice toward the more frequent occurrence of a similar event. Or, to understand the causes of melting sea-ice or severe drought, researchers can use sophisticated climate models to help identify — and potentially isolate — various factors that could individually contribute or dynamically interact to influence climate conditions in a particular region,” he says.
Evidence that climate change makes heatwaves, superstorms and droughts far more likely is growing. Earlier this year, scientists at the US National Oceanic and Atmospheric Administration (NOAA), the UK’s Met Office, and the research teams from 16 other global institutions tried to calculate how much climate change had possibly influenced 12 extreme weather events that occurred in 2012. By no means all could be linked, they concluded, but they agreed that it had helped raise the temperatures during the run of 100F (37.7C) days in last year’s US heatwave, and was behind the record loss of Arctic sea ice and the storm surge of hurricane Sandy, plus several other extremes. They were less certain about Britain’s wet summer and the drought in Spain.
“Determining the causes of extreme events remains challenging,” says Thomas R Karl, director of the national climate data center. Allen, whose work has shown that global warming tripled the odds of the severe 2010 Russian heatwave and tripled the risk of the widespread flooding in England in 2000, says extreme weather can be linked to climate change given enough computer time. He says the influence of climate change on typhoon Haiyan could be calculated in the future: “If we used the same tools as are used now to make seasonal weather forecasts, there would be a straightforward answer.”