Global Scorching & Hurricanes: What relationship?

2 articles: Agence France Presse & E magazine, 09/01/2005

Brace for More Katrinas, Say Experts
Agence France Presse

Tuesday 30 August 2005

Paris - For all its numbing ferocity, Hurricane Katrina will not be a unique event, say scientists, who say that global warming appears to be pumping up the power of big Atlantic storms.

2005 is on track to be the worst-ever year for hurricanes, according to experts measuring ocean temperatures and trade winds - the two big factors that breed these storms in the Caribbean and tropical North Atlantic.

Earlier this month, Tropical Storm Risk, a London-based consortium of experts, predicted that the region would see 22 tropical storms during the six-month June-November season, the most ever recorded and more than twice the average annual tally since records began in 1851.

Seven of these storms would strike the United States, of which three would be hurricanes, it said.

Already, 2004 and 2003 were exceptional years: they marked the highest two-year totals ever recorded for overall hurricane activity in the North Atlantic.

This increase has also coincided with a big rise in Earth's surface temperature in recent years, driven by greenhouse gases that cause the Sun's heat to be stored in the sea, land and air rather than radiate back out to space.

But experts are cautious, also noting that hurricane numbers seem to undergo swings, over decades.

About 90 tropical storms - a term that includes hurricanes and their Asian counterparts, typhoons - occur each year.

The global total seems to be stable, although regional tallies vary a lot, and in particular seem to be influenced by the El Nino weather pattern in the Western Pacific.

"(Atlantic) cyclones have been increasing in numbers since 1995, but one can't say with certainty that there is a link to global warming," says Patrick Galois with the French weather service Meteo-France.

"There have been other high-frequency periods for storms, such as in the 1950s and 60s, and it could be that what we are seeing now is simply part of a cycle, with highs and lows."

On the other hand, more and more scientists estimate that global warming, while not necessarily making hurricanes more frequent or likelier to make landfall, is making them more vicious.

Hurricanes derive from clusters of thunderstorms over tropical waters that are warmer than 27.2 C (81 C).

A key factor in ferocity is the temperature differential between the sea surface and the air above the storm. The warmer the sea, the bigger the differential and the bigger the potential to "pump up" the storm.

Just a tiny increase in surface temperature can have an extraordinary effect, says researcher Kerry Emanuel of the Massachusetts Institute of Technology (MIT).

In a study published in Nature in July, Emanuel found that the destructive power of North Atlantic storms had doubled over the past 30 years, during which the sea-surface temperature rose by only 0.5 C (0.9 F).

Emanuel's yardstick is storm duration and windpower: hurricanes lasted longer and packed higher windspeeds than before.

Another factor in destructiveness is flooding. Kevin Trenberth of the US National Center for Atmospheric Research suggests that hurricanes are dumping more rainfall as warmer seas suck more moisture into the air, swelling the stormclouds.

The indirect evidence for this is that water vapour over oceans worldwide has increased by about two percent since 1988. But data is sketchy for precipitation dropped by recent hurricanes.

"The intensity of and rainfalls from hurricanes are probably increasing, even if this increase cannot yet be proven with a formal statistical test," Trenberth wrote in the US journal Science in June. He said computer models "suggest a shift" toward the extreme in in hurricane intensities.

Stormy Weather: Can We Link It to Global Warming?
By Jim Motavalli

September/October 2005 Issue

There was some excellent reporting done by journalists caught in Hurricane Katrina. At the Mobile Register, Ben Raines was still at his desk, even though he could see dumpsters floating past his window, and his newspaper office had become "an island unto itself by a record storm surge approaching 13 feet." The AC, phones and electricity were out, but the Internet was on, allowing Raines to get his e-mails out. Meanwhile, among members of the Society of Environmental Journalists, an intense Category 3 debate raged about the relationship between global warming and the intensity of hurricanes.

Obviously, many factors affect hurricane damage. The National Oceanic and Atmospheric Administration (NOAA) says that 53 percent of the US population now lives along a coastline, and that the rate at which people are moving to the coast is larger than population growth. Much of the new development is right on the water's edge, making beachfront communities extremely vulnerable to storms. On the Mississippi coast between Gulfport and Biloxi, the world's largest manmade beach (60 miles long) is without sand dunes or salt marshes to deflect the brunt of hurricanes' fury.

E's Jennifer Vogel took on the subject of global warming and hurricanes in the May/June issue this year: "'There are a number of factors that go into making hurricanes,' says Ruth Curry, research specialist at Woods Hole Oceanographic Institute. Those factors include El Nio cycles, upper stratospheric circulation patterns and the amount of rainfall in the Sahel region of Africa. Sometimes they combine to create conditions ripe for hurricanes and sometimes they work against each other. The 2004 hurricane season is primarily attributed to alignment of these three critical elements.

"The general scientific consensus on climate change and hurricanes is this: Hurricanes won't necessarily become more frequent, but they will become more intense. While ocean and atmospheric circulation is the engine of a hurricane, heat is the fuel. 'In order to form, a hurricane must have ocean temperature of at least 80 degrees down to a depth of 164 feet,' says Curry. 'Sea surface temperatures all over the tropics are running 1.8 to 3.6 degrees above normal. This is due to global warming.' Thus, when other factors line up to form a storm, a warmer ocean means it will be all the more powerful and destructive."

And that is indeed what some scientists are now saying (though others remain skeptical). Katrina was one of the strongest hurricanes ever encountered in the Gulf of Mexico, and it wasn't alone. A study in the July issue of Nature reported that large tropical storms have increased by 50 percent in both the Atlantic and Pacific over the past 30 years. "These have been linked to rises in the temperatures of the ocean surfaces and warmer air temperatures," said the Times of London's online edition.

Kerry Emmanuel, an atmospheric researcher at the Massachusetts Institute of Technology (MIT) and the author of the Nature paper, told Scripps Howard News Service this week, "The intensity of hurricanes depends both on how much heat can be transferred from the ocean to the atmosphere-which depends on the temperature of the ocean-and on how high air rising in the eyewall can go. This depends on the temperature profile of the atmosphere." Emmanual added, "Future warming may lead to an upward trend in tropical cyclone destructive potential, and, taking into account an increasing coastal population [also] lead to a substantial increase in hurricane-related losses in the 21st century."

NOAA simulations indicate that global warming over the next 80 years could increase hurricane wind speeds an average of five to 10 percent, which means a jump of half a category in hurricane-intensity measurement. According to the Los Angeles Times, "Hurricane activity in the Atlantic has been higher than normal in nine of the last 11 years, said the National Oceanic and Atmospheric Administration. [In August], the agency raised its already-high hurricane forecast for this year to 18 to 21 tropical storms, including as many as 11 that would become hurricanes and five to seven that would reach major-hurricane status. That could make 2005 one of the most violent hurricane seasons ever recorded. A typical storm year in the Atlantic results in six hurricanes."

Environmental Defense has quantified the degree of ocean warming: "Ocean surface temperatures worldwide have risen on average 0.9 degrees Fahrenheit, or 0.5 degrees Celsius, and ocean waters in many tropical regions have risen by almost two degrees F (one degree C) over the past century. This is 30 times the amount of heat that has been added to the atmosphere, a significant amount even though the ocean has a lot more mass than the atmosphere. Also, the incidence of coral bleaching has increased worldwide since 1979, and scientists now generally link these mass bleachings to global warming. The largest bout of coral bleaching ever (1997-1998) occurred during the warmest 12-month period on record and in nearly every region of the world. It was a wake-up call that global warming was not just a distant threat."

The New Zealand Herald reports that Katrina's force should be seen against the backdrop of unusual weather events in Europe. "From deluged south-eastern Europe, where 43 died in tumultuous rainstorms, to tinder-dry Portugal, where 11 new fires flared [August 27] despite weeks of desperate firefighting, Europeans have been assaulted by weather extremes unknown for generations," the paper said. "Hardest hit was Romania, where 31 died, many of whom drowned when water engulfed their homes. Austria, Germany, Bulgaria and Switzerland reported 12 dead, with vast areas under water. Fears remain that floodwaters could cause the Danube to burst its banks and present further hazard. In the small Swiss town of Thun, the local football stadium was destroyed, a loss given international prominence by the club's qualification last week for the Champions League, in which it will take on Arsenal."

The behavior of the jet stream is also seen as a key factor in exacerbating the effects of storms. Wayne Elliott, a forecaster in the Meteorological Office in Exeter, England, notes that the stream did not come as far south as it was expected to do last fall, resulting in drought in Iberia and an unsettled northern Europe. "Such behavior is consistent with predictions by scientists who argue the climate is changing," Elliott said. "Global warming could be the key."

There have been a series of unusual weather events in the US, too. In a Boston Globe op-ed piece, Boiling Point author Ross Gelbspan wrote that anomalies this year included a two-foot snowfall in Los Angeles, a severe drought in the Midwest that dropped water levels in the Missouri River to their lowest on record, and a lethal heat wave in Arizona that killed more than 20 people in one week with temperatures over 110 degrees Fahrenheit.

"The hurricane that struck Louisiana yesterday was nicknamed Katrina by the National Weather Service," Gelbspan wrote. "Its real name is global warming...Unfortunately, very few people in America know the real name of Hurricane Katrina because the coal and oil industries have spent millions of dollars to keep the public in doubt about the issue."

Even if you don't agree that there's a clear link between increasing storms and global warming, you'd have to agree that Hurricane Katrina was really, really big, large enough for even some network newscasters to speculate about man-made planetary changes. But there are so many factors at work in the weather that's it's impossible to make definitive statements. Back to Jennifer Vogel's piece in E: "What is clear is this: Weather is a mix of constants and variables. The constants are those things that dictate general climate conditions, such as the proportion of the Earth's surface covered in water, atmospheric chemistry, and the orbit and tilt of the Earth, which shift slowly over the millennia. These factors tell us when the seasons will shift and which regions are defined as arid, temperate, tropical and arctic. The variables, such as temperature, humidity, and ocean and air currents, are derived from these climactic constants, giving rise to regionally specific daily weather patterns.

"Global warming will result in a shifting of the constants-those factors that we expect to be relatively stable-when the oceans expand, the land masses shrink, and the composition of the atmosphere changes. So within the span of a human lifetime, the implications for the weather may indeed be profound. If, as the saying goes, climate is what you expect and weather is what you get, then climate change means never knowing quite what to expect."