Is Global Warming Causing More Frequent, More Powerful Hurricanes?

July 21, 2010

A workshop held in Lloyd’s Old Library sought to answer that question, by examining the impact global warming could have on the hurricane season. Lloyd’s cited the fact that “analysis of weather patterns and damage losses over the last 100 years suggests that hurricanes are getting worse – and that rising temperatures are to blame.”

However, Dr. Chris Landsea, a scientist with the National Hurricane Center in Florida, who spoke at the workshop indicated that the “case is far from proven.” In fact Landsea “argues that hurricane activity may not be significantly different compared to that of a century ago.”

What seems to be changing is “our ability to identify and measure hurricanes – and the amount of material wealth that we put in their way.”

Dr. Landsea was speaking at a Lloyd’s Market Academy master class entitled: Hurricanes and Global Warming: Expectations Versus Observations. He pointed out that global warming is real and that temperatures have risen by 1 degree Celsius (1.8°F) over the last 100 years. “But while a rise in sea surface temperature and more moist air does make hurricanes stronger and more numerous,” he stated, “the greenhouse effect is not pronounced.”

Scientists’ models agree that the predicted change in global temperature will increase hurricanes’ strength by only 1 percent per degree of warming and that at the current rate of global warming windstorms will be just 3 percent stronger by the year 2100.

However, the models also suggest that a more turbulent atmosphere makes it more difficult for hurricanes to form – so there will be 40 percent fewer, albeit slightly stronger, hurricanes by the end of the century, Dr. Landsea said.

He also put a question mark over the use of damage losses to correlate global warming with hurricane intensity. He did agree, that with total losses running at an average of $20 billion per year in the period 1996 – 2005, it certainly was the most damaging decade in history.

“But it is to do with people having more stuff, bigger houses and multiple cars,” he pointed out. “Per capita wealth has increased over the last century, especially on the coast… in 1900 there were only about eight people living in Palm Beach, compared to 1.1 million now.”

To reinforce his point Dr. Landsea looked at the big loss making hurricanes in US history and adjusted them to today’s socio-economic landscape. He found that in terms of total losses Hurricane Katrina would be in third place behind the 1900 Galveston hurricane and the 1926 Miami windstorm, the latter creating around $150 billion in total losses.

Lloyd’s noted that “these numbers will come as no surprise to reinsurers who have been using catastrophe models to assess US Hurricane risk for nearly 20 years.” Landsea stressed that the “decade 1996–2005 was very damaging – but it isn’t an outlier. It is similar to what happened in the early 20th century.”

He also explained that finding climate change signals in the hurricane database is not clear cut either: “There has been a doubling of recorded hurricanes since 1871, but is something missing?” His theory is that the methods at scientists’ disposal to locate and measure hurricanes has improved hugely thanks to today’s array of coastal stations, buoys, aircraft, satellites and vessels at sea. “The hurricane database reflects all that increased sophistication,” he explained.

Summarizing his views on hurricane science, Dr. Landsea said that he expects fewer hurricanes over the next 90 years but with a small increase in intensity due to global warming. Storm surge will increase in line with slightly more intense storms and also the rise in sea levels; there will be a 10 percent increase in rainfall accompanying hurricanes. But there is no clear indication of changes in the genesis or track of hurricanes.

He added that “global warming isn’t having much effect on hurricane activity, which has been swinging back and forth for centuries. The disturbing news for all of you [those attending the presentation] is that these busy periods can last for 40 years – and we are in the middle of such a period right now.”

Lloyd’s Head of Exposure Management, Paul Nunn noted that “Dr. Landsea is a hurricane scientist, along with Knutson, Holland, Emanuel, Elsner, whose work is highly valued and closely followed by the cat modeling and reinsurance industry. Clearly the impact of climate change on hurricanes is complex and not yet clear cut; insurers must ensure their premiums cover the observed increase in risk, whatever the cause.”

Source: Lloyd’s of London

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