A Year on From Katrina…

A year after Katrina wrecked New Orleans, President Bush is touring the still devastated area. As his administration continues to receive a storm of abuse over its handling of the aftermath, a different storm is raging within the world’s scientific community. Are hurricanes becoming more vicious or more frequent?

Because the scientific consensus is that warm seas cause tropical storms, experts have long speculated that global warming, by driving up ocean surface temperatures, is bound to boost hurricanes. After Katrina this theory went into overdrive.

“We have known since 1987 that the intensity of hurricanes is related to surface sea temperature and we know that, over the last 15 to 20 years, surface sea temperatures in these regions have increased by half a degree Centigrade (0.9 F),” the British government’s chief scientist, David King, says. “So it is easy to conclude that the increased intensity of hurricanes is associated with global warming.”

One of the most respected voices in the debate is a Massachusetts Institute of Technology (MIT) professor, Kerry Emanuel, who began to warn of a link between hurricane intensity and global warming way back in 1987. According to Emanuel’s calculations, the power of tropical cyclones has roughly doubled since the 1950s. His measurement, called a power dissipation index, is based on storm intensity and duration.

He notes a significant rise over the last 30 decades — when Earth’s surface temperatures began to rise significantly — but especially since 1995, when global mean temperatures began to scale ever-higher annual peaks. “The large upswing in the last decade is unprecedented and probably reflects the effects of global warming,” says Emanuel.

Some scientists urge caution. They say hurricane hyperactivity, as was the case in 2004 and again in 2005, occurs in what appears to be decadal cycles and argue the meteorological data is just too recent or too sketchy to venture a firm conclusion.

Chris Landsea of the US National Hurricane Center notes that in 1975, only two geostationary satellites were available for monitoring hurricanes. Today, the figure is 10, providing a much better view of storms as they gather at sea and a far better imaging capability.

Landsea, whose co-authored paper appeared in July in the journal Science, acknowledges that global warming could be boosting hurricane winds, but only by one or two percent, which is far lower than Emanuel’s estimate.

So is climate change to blame for more violent and frequent hurricanes? As this year has seen record temperatures, we could see a record number of hurricanes. But will this happen? The hurricane season is now upon us, so we can but wait and see.