I've always been skeptical of the view that global warming leads to stronger hurricanes. The argument behind it seems overly simplistic -- hurricanes feed off warm water, so warmer sea surface temperatures will lead to more frequent and powerful storms.
Elsewhere in our solar system, the exact opposite seems true. Blisteringly hot Venus, for instance, seems to have extremely weak storm activity, whereas icy Jupiter has massive hurricanes that last centuries, large enough to swallow the entire earth several times over. This is only suggestive rather than conclusive, but clearly there's more to storm activity than just raw temperature.
Basic thermodynamics helps to explain why. Storms are essentially large heat engines. It's not temperature that drives a heat engine, but differences in temperature. Global warming, which warms the poles more than the equator, would seem to decrease the latitude-based differential that helps drive a hurricane's rotational energy.
So went my pet theory, at least— but no hard data supported it.
However, the other side had no hard data either. While climate modelers claimed global warming might strengthen storms, actual hurricanologists were adamant that no actual evidence existed. Some pointed to research on wind shear, which suggested that a warmer climate would reduce the conditions that allow hurricanes to form, despite warmer surface water.
In 2005, one hurricanologist, Emmanuel Kerry, broke ranks and claimed to have actual proof that global warming increased hurricanes. For this, Time Magazine quickly named him "Man of the Year". However, last year Kerry publicly recanted his view, admitting that his earlier work was flawed.
With Kerry's renunciation, hurricane scientists were unanimous in their view that global warming wouldn't lead to measurably stronger storms.
But could it do the reverse? Could global warming actually reduce hurricane activity? A pair of Chinese researchers now says this very well may be true, at least for some parts of the earth.
The researchers, using a new branch of science they call "paleotempestology", looked backwards through several thousand years of the earth's history. Using sedimentary deposits, core samples from caves, and other geological proxies, along with documented historical records of hurricane landfalls, they built the longest record of hurricane activity ever constructed. They then correlated it to the varying temperature at each period..
On the global level, the researchers found no link between climate and hurricane activity. Surprisingly, though, cold periods such as the Little Ice Age had the most hurricanes, at least in some regions, a result the team said "begs adequate explanation".
However, the study found a strong link between natural patterns such as El Nino and hurricanes, a clear pattern of rising and falling activity on decadal time scales. These oscillations, known as "ENSO", tended to suppress and enhance hurricanes on a regular cycle, with the cooler "la Nina" years having the most activity.
The research was published in the Chinese Science Bulletin, and can be viewed here.
quote: For many years, meteorologists have known that ENSO strongly affects tropical cyclone activity around the world. In some basins, El Niño events increase tropical cyclone activity (e.g., the central North Pacific near Hawaii, the South Paci fic, and the Northwest Pacific between 160 E and the Dateline) (Chan 1985; Chu and Wang 1997; Lander 1994). Tropical cyclone activity decreases in other basins (e.g., the Atlantic, the Northwest Pacific west of 160 E, and the Australian region) (Nicholls 1979; Revelle and Goulter 1986; Gray 1984). La Niña events typically bring opposite conditions.Hurricane activity in the Atlantic basin is affected by ENSO remotely through changes in the Atlantic atmospheric circulation, largely through the vert ical shear wind profile...
quote: Atlantic effect An effect similar to El Niño sometimes takes place in the Atlantic Ocean, where water along equatorial Africa's Gulf of Guinea becomes warmer and eastern Brazil becomes cooler and drier. This is related to El Niño's effect on the Walker circulation over South America, which causes the easterly trade winds in the western Atlantic Ocean region to strengthen.
quote: I'm just not convinced here
quote: It is now well-accepted that El Niño reduces hurricane activity in the Atlantic Basin