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A Colorful Climate-Hurricane Link

Michael D. Lemonick

By Michael D. Lemonick

The question of what will happen to hurricanes in a warming world is of obvious interest to people who live in the paths of these powerful storms, and those who insure them. It tends to come to mind most easily during a hurricane season that’s worse than average, like 2005 (the year of Katrina) or one that’s expected to be, like the current one.

All other things being equal, warmer sea-surface temperatures should lead to more powerful hurricanes, and the most current research suggests that’s true — but that changes in upper level wind patterns could lead to fewer hurricanes overall.

But a new study that will be published in a future issue of Geophysical Research Letters points to yet another factor that could influence hurricanes in a warming world, and it’s one that you might not readily think of: the ocean’s color.

It turns out that the tiny marine plants known as phytoplankton, which lie at the bottom of the marine food chain, but at the surface of our oceans, affect the ocean’s color quite significantly thanks to the chlorophyll they use to manufacture food. As the oceans have warmed during the past century, phytoplankton levels have diminished, and the water overall has become a little less green.

A team of climate modelers at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) led by Anand Gnanadesikan took that as a starting point for a simulation that looked at what might happen if phytoplankton levels plummeted. They examined a typhoon-forming region of the Pacific known as the North Pacific Subtropical Gyre, and plugged in both the actual ocean color as seen by satellites today, and the washed-out color you’d see in a phytoplankton-poor sea (assuming, of course, that the trash accumulating in the gyre doesn’t skew the calculations).

 

Satellite image of a phytoplankton bloom off the coast of Newfoundland on August 9, 2010, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. According to NASA, "The paisley pattern of peacock blue owes its color to phytoplankton." Credit: NASA.

Here’s the connection between a washed-out ocean and hurricanes: when you lose the phytoplankton, sunlight can penetrate deeper into the water, which means the water near the surface ends up being cooler than it otherwise would be. That should cut down on hurricanes in multiple ways, according to the American Geophysical Union press release:

“Cold water provides less energy; air circulation patterns change, leading to more dry air aloft which makes it hard for hurricanes to grow. The changes in air circulation trigger strong winds aloft, which tend to prevent thunderstorms from developing the necessary superstructure that allows them to grow into hurricanes,” the release states.

Sure enough: hurricane formation dropped by 70 percent in the colorless simulation, dramatically reducing the potential risk to China and Japan. The risk rose for Southeast Asia and the Philippines, though, due to an increase in hurricane formation just outside the gyre, but overall the incidence of hurricanes was still significantly less.

If further research confirms this result, you could think of it as a little bit of good news about global warming — that is, if you consider a major hit to the marine food chain to be good news…

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Boston: July Days Over 90 Degrees By mid-century in Boston, the sweltering heat of July 2010 may be thought of as cooler-than-average conditions

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