Dr. Christy has drawn the scorn of his colleagues partly because they believe that so much is at stake and that he is providing legitimacy to those who refuse to acknowledge that. If the models are imprecise, they argue, the science behind them is compelling, and it is very likely that the world has only a few decades to stave off potentially catastrophic warming.

And if he is wrong, there is no redo.

“It’s kind of like telling a little girl who’s trying to run across a busy street to catch a school bus to go for it, knowing there’s a substantial chance that she’ll be killed,” said Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology. “She might make it. But it’s a big gamble to take.”

By contrast, Dr. Christy argues that reining in carbon emissions is both futile and unnecessary, and that money is better spent adapting to what he says will be moderately higher temperatures. Among other initiatives, he said, the authorities could limit development in coastal and hurricane-prone areas, expand flood plains, make manufactured housing more resistant to tornadoes and high winds, and make farms in arid regions less dependent on imported water — or move production to rainier places.

Dr. Christy’s scenario is not completely out of the realm of possibility, his critics say, but it is highly unlikely.

In interviews, prominent scientists, while disagreeing with Dr. Christy, took pains to acknowledge his credentials. They are substantial: Dr. Christy, 63, has researched climate issues for 27 years and was a lead author — in essence, an editor — of a section of the 2001 report of the United Nations Intergovernmental Panel on Climate Change, the definitive assessment of the state of global warming. With a colleague at the University of Alabama in Huntsville, Dr. Roy Spencer, he received NASA’s medal for exceptional scientific achievement in 1991 for building a global temperature database.

That model, which concluded that a layer of the atmosphere was unexpectedly cooling, was revised to show slight warming after other scientists documented flaws in its methodology. It has become something of a scientific tit for tat. Dr. Christy and Dr. Spencer’s own recalculations scaled back the amount of warming, leading to further assaults on their methodology.

Dr. Christy’s response sits on his bookshelf: a thick stack of yellowed paper with the daily weather data he began recording in Fresno, Calif., in the 1960s. It was his first data set, he said, the foundation of a conviction that “you have to know what’s happening before you know why it’s happening, and that comes back to data.”