María Amparo Lasso* - Tierramérica

MEXICO CITY, Nov 8 2005 (IPS) — This year’s record-breaking hurricane season in the North Atlantic, with storms like Katrina, Rita and Wilma wreaking unprecedented destruction, can only be partially attributed to global warming, according to scientists consulted by Tierramérica.

Hurricane Wilma, which crashed into Mexico’s Yucatan peninsula after pounding Cuba and Florida with torrential rains and gusting winds, was at one point the most powerful Atlantic hurricane on record, with an all-time low barometric pressure of 882 millibars and winds of up to 270 km an hour.

Wilma destroyed hundreds of hotels and tourism workers’ homes in the Mexican resort area of Cancún, turned central Havana streets into virtual rivers, and left millions without electric power in Miami, Florida..

Thousands of people will continue to suffer its devastating effects for months to come.

But are these harrowing scenes of destruction a direct result of the global warming process brought about by human activity, as some observers and environmental groups maintain?

The answer is no, according to Judith Curry, a U.S. scientist who has gained notoriety in recent months precisely because of her efforts to highlight the correlation between tropical cyclones and the warming of the earth’s atmosphere.

“We can’t directly attribute the intensity of a single storm, or storms in a single season, to global warming,” said Curry, chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta, in an interview with Tierramérica.

Global warming is a consequence of the build-up of what are known as greenhouse gases, like carbon dioxide and methane, which trap the Sun’s heat in the Earth’s atmosphere.

The primary source of greenhouse gas emissions is the burning of fossil fuels (oil, natural gas and coal). This warming process has led to a rise in air and sea temperatures and variations in weather patterns collectively known as climate change.

“This year, in the North Atlantic and Caribbean, hurricanes have been especially intense since the sea surface temperatures have been warmer than usual and atmospheric circulation patterns have been favourable for hurricane intensification,” said Curry.

Hurricanes form at sea when surface temperatures rise above 26.5 degrees Celsius, and draw their destructive power from the warm, moist air above the water.

The 2005 Atlantic hurricane season, which does not officially end until late November, has already set a new record for the number of storms in a single year, with the formation last week of Tropical Storm Beta, this season’s 23rd. The previous record dated back to 1933, when 21 storms were registered.

There are numerous reasons for this, according to Curry. “The exceptional year can probably be attributed to a combination of greenhouse warming, El Niño, and the North Atlantic Oscillation,” she said.

The North Atlantic Oscillation (NAO) is a large-scale pattern of natural climate variability that has been shown to fluctuate across multi-decade cycles.

Another oft-cited scientist, Kerry Emanuel of the Massachusetts Institute of Technology (MIT), agrees with Curry.

In the Atlantic, where only 11 percent of the world’s tropical storms are recorded, the intensity of hurricanes corresponds to natural cycles. “It’s difficult to see a signal from global warming there,” remarked Emanuel.

“The terrific damage from these storms (Katrina, Rita, Wilma) depended on the fact that they made landfall where and when they did, and this is largely a matter of chance,” he told Tierramérica.

Both Curry and Emanuel have been under the spotlight in recent months following the publication of separate studies, based on different methodologies, that provide the first conclusive evidence of an increase in the intensity (not the number) of tropical cyclones around the world – including North Atlantic hurricanes – in the last 35 years, as a result of the rise in average sea surface temperatures.

Curry was co-author of a study by scientist Peter Webster and colleagues published by the journal Science in September, while Emanuel’s study was published by Nature magazine in July.

Both believe that the worldwide increase in sea surface temperatures over the last few decades is partially a result of global warming, although Curry stressed that there is no way to determine its precise share of the responsibility. And both experts were cautious to avoid blaming this man-made phenomenon for the destructive force of any specific hurricane.

Emanuel also emphasised that there is no evidence of an increase in the number of storms around the planet.

“There are about 90 tropical cyclones worldwide per year, and this frequency of storms has been rock steady,” he stated.

The studies published by Emanuel and Curry and her colleagues served to heat up the highly politicized debate over climate change in the United States, where the George W. Bush administration has withdrawn the U.S. signature from the Kyoto Protocol aimed at curbing emissions of the greenhouse gases, despite being the world’s largest single source of these emissions.

After Hurricane Katrina struck the U.S. Gulf Coast on Aug. 29, unleashing death, destruction and 30 billion dollars in damages on New Orleans and other nearby towns and cities – as well as dealing a heavy political blow to the Bush administration – the debate over the role of global warming and climate change in this catastrophic storm sharply divided the scientific community.

Some specialists have even refuted the claim that hurricanes have increased in intensity over the last 35 years, criticizing Emanuel and Curry et al for limiting their studies to satellite data dating back to 1970, when there is information gathered by aircraft over the North Atlantic going back to at least 1945. According to their detractors, these data prove that there have been periods of storm activity in previous decades just as intense as what is currently being witnessed.

A high degree of hurricane activity was recorded between the 1940s and 1960s, followed by a period of relative calm from the 1970s to the 1990s, until the current cycle of renewed intensity began in 1995, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

Jorge Sánchez-Sesma of the Mexican Institute of Water Technology agrees. “The frequency of hurricanes in the 1950s and 1960s was intense, and we are now returning to those conditions. There is a significant contribution made to global warming by non-anthropogenic factors (not caused by human activity) that have not been taken into account,” he said.

Moreover, “the population and cities have grown significantly in the southeast coastal areas of the United States and on the coasts of Quintano Roo (on the Yucatan Peninsula) in Mexico, which makes us more exposed than in the past,” he added.

For his part, Patrick Michaels, a professor at the University of Virginia and researcher at the Cato Institute, a libertarian think tank based in Washington, firmly maintains that global warming had absolutely no influence on either Hurricane Wilma or Katrina.

Michaels is one of the most outspoken critics of what he calls the “media hysteria” stirred up around global warming, the political motives behind climate change research, and the millions of dollars in taxpayers’ money devoted to this field in the United States.

The federal outlay on climate research is now almost the same as the amount given to the National Cancer Institute, he commented to Tierramérica.

If hurricanes had actually doubled in power, the losses in the insurance industry would be catastrophic, and this is not the case, he added.

(*María Amparo Lasso is editorial director of Tierramérica. Additional reporting by Diego Cevallos in Mexico. Originally published Oct. 29 by Latin American newspapers that are part of the Tierramérica network. Tierramérica is a specialised news service produced by IPS with the backing of the United Nations Development Programme and the United Nations Environment Programme.)