Dr. Christy is an outlier on what the vast majority of his colleagues consider to be a matter of consensus: that global warming is both settled science and a dire threat. He regards it as neither. Not that the earth is not heating up. It is, he says, and carbon dioxide spewed from power plants, automobiles and other sources is at least partly responsible.
But in speeches, congressional testimony and peer-reviewed articles in scientific journals, he argues that predictions of future warming have been greatly overstated and that humans have weathered warmer stretches without perishing. Dr. Christy’s willingness to publicize his views, often strongly, has also hurt his standing among scientists who tend to be suspicious of those with high profiles. His frequent appearances on Capitol Hill have almost always been at the request of Republican legislators opposed to addressing climate change.
“I detest words like ‘contrarian’ and ‘denier,’ ” he said. “I’m a data-driven climate scientist. Every time I hear that phrase, ‘The science is settled,’ I say I can easily demonstrate that that is false, because this is the climate — right here. The science is not settled.”
Dr. Christy was pointing to a chart comparing seven computer projections of global atmospheric temperatures based on measurements taken by satellites and weather balloons. The projections traced a sharp upward slope; the actual measurements, however, ticked up only slightly.
Such charts — there are others, sometimes less dramatic but more or less accepted by the large majority of climate scientists — are the essence of the divide between that group on one side and Dr. Christy and a handful of other respected scientists on the other.
“Almost anyone would say the temperature rise seen over the last 35 years is less than the latest round of models suggests should have happened,” said Carl Mears, the senior research scientist at Remote Sensing Systems, a California firm that analyzes satellite climate readings.
“Where the disagreement comes is that Dr. Christy says the climate models are worthless and that there must be something wrong with the basic model, whereas there are actually a lot of other possibilities,” Dr. Mears said. Among them, he said, are natural variations in the climate and rising trade winds that have helped funnel atmospheric heat into the ocean.
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.