Scientists have disagreed about whether global warming is causing hurricanes to be more frequent and powerful. Now a study using a new measuring technique, published in a major peer-reviewed journal, has produced a longer historical data record that authors say shows the connection.
"One of the major unanswered questions about climate change is whether hurricanes have become more frequent and stronger as the world has warmed. Until now, there hasn’t been enough evidence to settle the question, but a report published Monday in Proceedings of the National Academy of Sciences may have changed all that. Using an entirely new method of tallying hurricane power and frequency, a team of scientists say that hurricanes are, indeed, more of a danger when ocean temperatures are higher. 'In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years,/ the report says.
Until now, the problem with such calculations is that until satellites came along in the 1970’s, nobody knew for sure how many hurricanes formed during a given year. That’s because some hurricanes never strike land, and unless a ship or a plane happened upon one of these storms, nobody might even know it had ever existed, and certainly not how strong it was.
The record from the '70's onward is much more complete — but since hurricane numbers wax and wane based on a natural cycle, that’s not long enough to see if there’s a warming-related pattern on top of ordinary fluctuations. Ocean temperatures fluctuate according to natural cycles as well, although studies have shown an overall increase in North Atlantic sea surface temperatures, a trend that has been linked to manmade global warming.
But Alex Grinsted of the University of Copenhagen and his colleagues came at the problem in an entirely different way. They looked not at hurricanes themselves, but at the storm surges tropical storms drive before them as they come ashore, and surges have been reliably measured by devices known as tide gauges all the way back to the 1920's."