DENVER — Challenging the climate science community, noted hurricane forecaster William Gray said that global ocean currents, not human-produced carbon dioxide, are responsible for global warming, and the Earth may begin to cool on its own in five to 10 years.
Gray, a Colorado State University researcher best known for his annual forecasts of hurricanes along the U.S. Atlantic coast, also said increasing levels of carbon dioxide in the atmosphere will not produce more or stronger hurricanes.
He said that over the past 40 years the number of major hurricanes making landfall on the Atlantic coast has declined compared with the previous 40 years, even though carbon dioxide levels have risen.
Gray, speaking Friday to a group of Republican state lawmakers, had harsh words for researchers and politicians who say manmade greenhouse gases are responsible for global warming.
"They're blaming it all on humans, which is crazy," he said. "We're not the cause of it."
Many researchers believe warming is causing hurricanes to get stronger, while others are not sure.
A study published last week suggested warming might make it more difficult for hurricanes to form because it produces more vertical wind shear, which can weaken hurricanes.
But the researchers, Gabriel A. Vecchi of the National Oceanic and Atmospheric Administration and Brian J. Soden of the University of Miami, said it was unclear whether the dampening effects of wind shear would cancel out the boost that warmer water gives hurricanes.
Gray complained that politics and research into global warming have created "almost an industry" that has unfairly frightened the public and overwhelmed dissenting voices.
He said research arguing that humans are causing global warming is "mush" based on unreliable computer models that cannot possibly take into account the hundreds of factors that influence the weather.
Gray said ocean circulation patterns are behind a decades-long warming cycle. He has argued previously that the strength of these patterns can affect how much cold water rises to the surface, which in turn affects how warm or cold the atmosphere is.
He also disputed assertions that greenhouse gases could raise global temperatures as much as some scientists predict.
"There's no way that doubling CO2 is going to cause that amount of warming," he said.
Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in Boulder, said natural changes in the environment cannot account for the magnitude of global warming in the past four decades.
"Since about 1970, the global temperature change is outside of the range of natural variability," he said in an interview.
He also challenged Gray's assertion that ocean currents have more effect on temperatures than carbon dioxide and other greenhouse gases.
"Global warming is pervasive. It has an influence on everything," Trenberth said. "It has an influence on ocean currents, it has an influence on hurricanes, it has an influence on rainfall."
Trenberth said computer climate models are the best quantitative tools available for predicting climate change. "They have been getting better over time," he said.
Gray said warming and cooling trends cannot go on indefinitely and that he believes temperatures are beginning to level out after a very warm year in 1998.
"We're going to begin to see some cooling," he said.
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