SOUTH KINGSTOWN — Michael E. Mann, a Nobel Prize-winning scientist, had just spent an hour explaining why he thinks there is virtual scientific consensus that people are causing the earth to warm and sea levels to rise, when a self-described “left-leaning, pro-environment person,” a meteorologist, rose to angrily dispute him.

The critic said thousands of scientists disagree with Mann’s contention that carbon dioxide is causing climate change. Others have discredited Mann’s figures on unprecedented temperature hikes. And some wish he would leave his university, Penn State.

The critic didn’t give his name. But later Herb Stevens, a North Kingstown meteorologist who makes his living as the “Skiing Weatherman” on many local television stations, confirmed he was the critic. “I’m not some crackpot,” he said. “I’ve spent a lot of time in the last 10 years researching this matter. It is the greatest hoax perpetrated on mankind.”

Mann, who has been vilified by Sen. James Inhofe, R-Okla., and a host of other climate skeptics, responded calmly before an audience of nearly 1,000 on Tuesday.

Natural forces don’t account for the warming that is being observed, he said. Only carbon dioxide fits. Then he added:

“A fossil-fuel funded amateur has a Web site that vilifies scientists in my field,” he said. Questions about his data were rejected, he said, by the National Academy of Science and by the United Nations’ International Panel on Climate Change.

“I don’t think by any stretch of the imagination has our science been discredited, except perhaps by some far-out fringe of the blogosphere.”

Mann got a big round of applause.

He later said he is used to the attacks. Climate change skeptics see that they are losing the scientific arguments, he said, so they are stepping up ad hominem attacks on scientists.

Mann’s presentation was the third in a series on climate change offered by the Fall 2008 Honors Colloquium at the University of Rhode Island. He named it after his new book of the same title: Dire Predictions: Understanding Global Warming.

He largely stuck to an overview of climate change science. But he also pointed to his critics, especial Inhofe, who called the climate change story “the greatest hoax ever perpetrated on the American people.”

Mann said early models predicting climate change are being validated by melting sea ice and glaciers around the world, rising sea levels and more unpredictable weather. And more warming is expected, he said, no matter how much the world reduces its emissions of greenhouse gases.

“In the last 10,000 years there is nothing like the spike we are seeing today,” Mann said. “Over 400,000 years there have been periods of warming and cooling, but nothing like we’re seeing today.”

He added that the globe is not warming uniformly. Land masses are warming more than oceans. But steadily, around the world, the warming is increasing.

He showed pictures of the snows of Mount Kilimanjaro disappearing. They have been there for 12,000 years, and at the current rate of decline, Mann said they will be gone in two decades.

He said his so-called “hockey stick” curve on a graph, which shows warming sloping gently upward, and then shooting straight up, has been criticized by many skeptics, but supported by 10 more studies in the last decade.

One questioner said it was well known in the scientific community that disappearing snows of Kilimanjaro have nothing to do with climate change.

But Mann said the questioner was wrong. The snows are melting and evaporating, both because of climate change, he said.

People have to do something, he said, to reduce carbon emissions.

Another skeptic, who said his name is Dean Fachon, handed out cards outside the hall directing people to his Web site, netscribe.com.

One student tossed Fachon’s card back at him, asking “Why are you doing this?”

Stevens, contacted yesterday, said one student followed him outside of the hall, asking for more information. He said the idea that the debate is over is “beyond arrogant.” He directed the student to a Web site: www.icecap.us.

plord@projo.com