No rise in storms from global warming

By George E. Beetham Jr.
Adventures on Earth column for the Nov. 17 edition of The Review
Conventional wisdom held that global warming would mean higher sea surface temperatures and thus more and stronger hurricanes. It turns out conventional wisdom was wrong.
While the first part of the statement is true, warmer sea surface temperatures are virtually certain, the threshold for tropical cyclone formation would rise from the current 80 degrees Fahrenheit.
This means it would take warmer sea surface temperatures to trigger storm formation.
Hurricanes form as low pressure systems move over warm, tropical seas. At 80 degrees, the warm water evaporates and the warm, moist air rises, eventually forming clouds. The counter clockwise rotation of air around the low and the rising warm air funnel more and more moisture into the clouds.
As the speed of winds rotating around the low increase the storm draws more warm air inward. The rotation contracts, and eventually an eye develops.
Researchers at the University of Hawaii’s International Pacific Research Center (IPRC) have discovered that the threshold sea surface temperature for the convection of warm, moist air is rising at the same rate as the warming of the tropical seas.
The researchers studied records dating back 30 years and found that the threshold temperature closely followed the increase in average sea surface temperatures in the tropics. Both have been rising at the rate of one degree centigrade per decade.
Nat Johnson, lead author of the study and a postdoctoral fellow at the IPRC, said, “The correspondence between the two time series is rather remarkable. The convection threshold and average sea surface temperatures are so closely linked because of their relation with temperatures in the atmosphere extending several miles above the surface.”
Johnson and co-author Shang-Ping Xie, professor of meteorology at IPRC and University of Hawaii Manoa, found that temperatures in the upper atmosphere have been rising at the same rate as sea surface temperatures and the convection threshold.
The study means that global warming will not bring more frequent hurricanes as conventional wisdom had supposed.
The study also means there is no linkage between the increase in storm frequency in recent decades and global warming. Instead, tropical cyclone formation tends to run in a cycle of approximately 70 years.
The current cycle began with a peak about 1950 and the next peak would occur in 2020, assuming the 70-year cycle to be accurate.
One of the difficulties in tropical cyclone prediction is that accurate records only go back to the middle of the last century. Models of cyclone formation are thus based on relatively little data.
Still, the cyclical nature of cyclone formation appears to hold true in the Atlantic.
What meteorologists still have not determined is what effect, if any, global warming will have on storm intensity.
As scientists continue to focus on global warming and the effects it will have on weather, that question too will likely be answered sooner rather than later.
For the record, the Atlantic hurricane season is winding down, with just two weeks left before it ends. While it was a busy season, it fell far short of 2005, the record year.
This year there were 19 named storms of which seven were hurricanes with four of those reaching Category 4.
In 2005 there were 28 named storms (one of which was sub tropical) and 15 hurricanes, of which eight were major storms.