GREENBELT, Md. — I’M a climate scientist and a former astronaut. Not surprisingly, I have a deep respect for well-tested theories and facts. In the climate debate, these things have a way of getting blurred in political discussions.

In September, John P. Holdren, the head of the White House Office of Science and Technology Policy, was testifying to a Congressional committee about climate change. Representative Steve Stockman, a Republican from Texas, recounted a visit he had made to NASA, where he asked what had ended the ice age:

“And the lead scientist at NASA said this — he said that what ended the ice age was global wobbling. That’s what I was told. This is a lead scientist down in Maryland; you’re welcome to go down there and ask him the same thing.

“So, and my second question, which I thought it was an intuitive question that should be followed up — is the wobbling of the earth included in any of your modelings? And the answer was no...

“How can you take an element which you give the credit for the collapse of global freezing and into global warming but leave it out of your models?”