What’s Going on with Hurricanes?

With Wilma, 2005 ties 1933 for the year with the most (21) named storms (going back to 1851). The difference is that 1933 had no category 4 or 5 storms while 2005 had two category 4s and three category 5s—an all-time record for 5s. What’s going on?

The Increase in Hurricane Strength is World-Wide
Partly it may be bad luck and partly it’s a predictable, decades-long Atlantic hurricane cycle. But that does not mean global warming isn’t part of it. The recent Sciencearticle found a similar increase in category 4 and 5 hurricanes in all six hurricane basins world wide. That’s not from the Atlantic cycle, and it’s very unlikely to be just bad luck.

To say how much impact global warming is having, two questions must be answered.
• How much has human activity warmed tropical oceans?
• How much does hurricane destructiveness increase per degree of warming?

Human-Caused Warming Has Been Very Slight
The consensus is that tropical oceans are about 0.5° C (slightly less then 1° F) warmer. This is so little that computer models of hurricanes predict only a very slight increase in hurricane power. 

But Hurricanes are Very Sensitive to Tropical Sea Temperature
That’s where Dr. Kerry Emanuel’s Nature article comes in. He did not look for global warming; he just looked at how hurricane power has related to tropical sea temperature for the last 61 years. His data show the computer models are wrong, and a 0.5° C causes a much larger impact.  

What’s the bottom line? 

Global warming is obviously melting glaciers in Montana’s Glacier Park and the Canadian Rockies, but the warming is so slow that no major effect has been demonstrated. The consensus is that since 1900, the oceans have warmed by slightly less than 1 degree F and the climate slightly more.

But hurricanes are different. Small changes in tropical sea temperatures shut them off completely every winter. In the 1930s-50s Atlantic hurricanes were intense and then tapered off to a low in the 1970s. The cycle reversed, and by the mid-1990s they were back. Most of this was caused by a natural ocean cycle, a fall and rise in sea temperature of about 1 degree fahrenheit that has been going on for centuries. But this time, it’s more intense and the temperature is higher than last time. The difference appears to be caused by a little global warming, but with hurricanes, the consequence is not small.

The multi-decade Atlantic ocean cycle that the goverment likes to blame for all of the change is real. But it can’t explain why hurricane intensity has risen even more in five other hurricane basins, two in the Indian Ocean, two in the North Pacific and one in the South Pacific. There’s a chance the science is wrong and this is nothing unusual.  But there’s a better chance we’re seeing the first large-scale impact of global warming.

In spite of the natural ocean cycle and global warming, the dramatic increases in US hurricane damage is mainly due to the increases in coastal populations since the 1940s. Because hurricanes are so unpredictable, no specific cost can be attributed to global warming. This means it is just as wrong to say there has been no cost as to say it was 20% or 40% of hurricane damage in recent years. Without global warming, Katrina almost certainly would not have happened, but something else would have, and it might have been worse … or better. We just don’t know.

What’s Going on with Glaciers?

A new study by scientists at University of Alaska Southeast, compared radar mapping data from a space shuttle mission six years ago with air photos taken between 1948 and 1979, of Alaskan glaciers.  Motyka, UAF colleague Chris Larsen and three other scientists pinpointed the extent of the glaciers’ volume change. They found that 95 percent of Southeast Alaska’s glaciers  are thinning. Some glacier surface elevations had dropped as much as 2,100 feet since 1948, such as the Muir Glacier in the popular Glacier Bay National Park and Preserve.  

Southeast Alaska’s glaciers are very sensitive to climate change because of their large surface areas at low elevations. In Juneau, the winters have been getting warmer and rainier — 6.8 degrees warmer compared to 50 years ago, according to Laurie Craig, a naturalist for the Tongass National Forest. Those warmer temperatures can disrupt a glacier’s surface mass balance, the balance achieved between the melting period of summer and accumulation period of winter.