The world really is getting stormier. US tide records have provided compelling evidence that global warming is making large storms and cyclones more frequent. If current trends continue, the US will be battered increasingly often, and by more big storms like Hurricane Katrina.
Many studies have claimed that hurricanes are becoming more common, or stronger, but they were open to challenge because older hurricane records are less reliable than modern satellite data.
鈥淭he earlier evidence is quite weak,鈥� says of the University of Copenhagen in Denmark. 鈥淚t鈥檚 clear there鈥檚 been an increase in the number of cyclones in the Atlantic, but we know we鈥檝e missed some in the past.鈥�
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Consistent method
Grinsted鈥檚 approach should be less prone to bias. 鈥淥ur data are measured in a consistent way all the way through from 1923, so we know the increases we see are real,鈥� he says.
Rather than records of hurricanes, Grinsted looked at the storm surges they cause. 鈥淲hen you have a very large cyclone or hurricane, there鈥檚 very low pressure that sucks up the ocean into a little hill,鈥� he explains. 鈥淲hen it hits the coast, it creates a storm surge.鈥�
He chose six tide gauges along the hurricane-prone Gulf and east coasts of the US. Grinsted used records of recent storms to work out what storm surges look like in the data, then looked for this signature in older records. In this way, Grinsted identified all the surges dating back to 1923, even though many of the corresponding hurricanes had been missed by meteorologists.
The study predicts that by 2100, the number of cyclones and hurricanes causing large tidal surges will average 9.5 per year, compared to 5.4 per year in 1923. It also suggests that storms the size of Hurricane Katrina, which devastated New Orleans in 2005, are twice as frequent in warm as in cold years. This suggests more big storms will brew up if the world continues warming.
Heat-driven
The study provides important additional evidence for climate-change-induced increases in hurricane power, says hurricane expert of the Massachusetts Institute of Technology.
鈥淚 like the approach taken,鈥� says of Florida State University in Tallahassee. Similar increases have been observed in satellite data, but Grinsted鈥檚 records extend much further back in time.
Elsner says that the results are consistent with Emanuel鈥檚 鈥渉eat-engine theory鈥� of hurricane intensity, which holds that ocean warming drives increases in hurricane and cyclone intensity.
Journal reference: , DOI: 10.1073/pnas.1209542109
