With New Orleans left a disaster area in Hurricane Katrina’s wake, the debate about global warming’s effects is being hotly renewed among scientists.

Global warming is the term atmospheric scientists use to describe the increase over time of the average temperature of Earth’s atmosphere and oceans. Scientists generally agree that global warming is occurring, most notably the U.N. Intergovernmental Panel on Climate Change.

“We know that global warming is happening because of humans burning fossil fuels which puts out carbon dioxide – and sea temperatures have risen by a half-degree Celsius over the last 30 years,” said Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colo.

Much of the debate centers around what the net effects of increased carbon dioxide in the atmosphere are. A number of scientists, including Trenberth, now believe that global warming is making hurricanes stronger. Trenberth said Katrina’s ferocity was “definitely” affected by global warming.

“The fuel for hurricanes comes directly from sea surface temperatures, which are higher,” said Trenberth in describing the beginning stages of tropical storms that can grow into hurricanes.

Surface pressures fall as water vapor condenses and releases latent heat, starting a chain reaction whereby the increased temperatures cause surface pressures to decrease further, leading to more thunderstorms and stronger winds.

“Latent heat is the fuel that drives the storm – the most likely thing is that we’ll see more of them,” Trenberth said.

Thomas Knutson, a research meteorologist in the Climate Dynamics and Prediction Group at the National Oceanic and Atmospheric Administration in Princeton, N.J., is inclined to agree that global warming is having an effect on hurricanes.

“I think it’s plausible that global warming is making some contribution toward Katrina and others at this point because the tropical Atlantic has been warming – outside the range of natural viability,” Knutson said. “My interpretation is that perhaps global warming is already affecting things in such a way as to load the dice toward higher hurricane intensity.”

Knutson said that while it’s currently impossible to prove whether Katrina’s intensity was related to global warming, it definitely warrants further study.

“Our work is more along the lines of future projections, but it (Katrina) is an important data point that we need to try and understand,” said Knutson, whose studies project a half a category increase in hurricanes 80 years from now.

Placing blame

Trenberth blames the Bush administration for contributing to global warming via its decision to reject participation in the Kyoto Protocol, an international treaty to reduce carbon dioxide emissions.

“The U.S. has not proposed any viable alternative to Kyoto – this administration is very irresponsible,” Trenberth said.

He dismissed the Bush administration’s suggestion that abiding by the treaty would hurt the national economy.

“You don’t think Hurricane Katrina causes a hit on the economy? There is no basis for that (suggestion) whatsoever because the alternative is even worse,” Trenberth said in reference to New Orleans. “You have two choices – either you try and stop it (global warming), or you should be planning, and in fact they’ve done neither.”

But there is far from a consensus in the scientific community on the topic of global warming. Some scientists simply do not believe that humans can have an impact on Earth’s weather.

Global warming is not proven, said Jay Lehr, scientific director of the Heartland Institute, a non-profit research center in Chicago, Ill.

“We have 250,000 years of weather records from ice cores in Greenland,” he said. “Air bubbles in the cores have carbon dioxide – we can date them with radio-isotope dating. We get a pretty good idea of the temperature of air in the bubbles- there is actually not a direct relation proven of increased carbon dioxide leading to increased temperatures.”

Lehr acknowledges that warmer temperatures could affect hurricanes, but he doubts mankind has any role in the process.

“A slightly warmer temperature could have an impact on hurricanes, but it has no relation to man,” Lehr said. “The total carbon dioxide in the atmosphere was about four percent. Man has increased that by about 30 percent to bring carbon dioxide to five percent – so we’re only responsible for one one-hundredth of the overall greenhouse gases.”

Lehr said it’s arrogant to think that humans have any control over the weather and that the global warming scare is about money.

“The government gives $5 billion in scientific research money to those looking to prove global warming,” Lehr said. “Environmental advocates use global warming as a cash cow to get funding.”

On the horizon

Renowned meteorologist William Gray, who became a pioneer in hurricane forecasting while working as a professor in atmospheric science at Colorado State University, shares the opinion that the effects of global warming on weather are negligible and that money is a factor in the push for global warming research.

But while Gray views the current hurricane activity as part of a historical cycle rather than an effect of global warming, he still foresees big trouble on the horizon.

“Our feeling is that the United States is going to be seeing hurricane damage over the next decade or so on a scale way beyond what we have seen in the past,” Gray said in the September 2005 issue of Discover Magazine.

Thomas W. Schmidlin, chair of Kent State’s geography department and holder of a Ph.D. in atmospheric sciences, acknowledges global warming as a contributor. But like Gray, he believes that a multi-decadal pattern where hurricanes grow stronger in certain cycles of time is the main factor.

“To say global warming is the reason (for stronger hurricanes) is insufficient,” Schmidlin said. “The ’50s and ’60s were above normal, very active. From 1970-1994, the numbers were way down. In 1995 it sort of switched.

“It is affected by sea surface temperatures, but that’s not controlled just by global warming.”

Schmidlin cited wind shear, currents, rains, evaporation and the general atmospheric pattern over the tropical Atlantic as other important factors. He also acknowledged that it’s reasonable to suggest global warming is adding to the intensity of the multi-decadal cycle, but the warming is probably less important than the cycle itself.

“There’s no conclusive proof that Katrina was caused by global warming, but it certainly is consistent with what scientists are saying about bigger storms,” said Kert Davies, Greenpeace’s climate campaign coordinator.

Regarding evidence for the threat of global warming, Davies said Greenpeace has been talking to the insurance industry for years in an effort to follow the money to see what the insurance industry really thinks about the issue. Davies points to “re-insurance” agencies such as Swiss Re and Munich Re, companies that insure other insurance companies.

“They have sent out real freak-out notes about global warming,” Davies said.

Contact public affairs reporter Greg M. Schwartz at [email protected].