Just before Congress began tackling climate change legislation this week, the Pew Research Center released a new survey showing a sharp decline in public’s belief that global warming is real.

Two years ago, 77 percent of Americans who were polled said there was solid evidence of global warming. Last year 71 percent said so. Now it is 57 percent.

Pew noted that its poll was released a day after leaders of 18 prominent scientific organizations signed a “Dear Senator” letter reaffirming what they see as scientific consensus on climate change. (One of the 18 signers is University of Minnesota Prof. Douglas Arnold, who is president this year of the Society for Industrial and Applied Mathematics.)

Why are the public and the scientists moving in opposite directions on this issue?

I don’t know. And Pew researchers said they were puzzled too.

One hint, though, comes from a different study Pew released last month. This one was a News IQ quiz.

Here’s one of the 12 multiple choice questions on the quiz: Does the so-called “cap and trade” legislation being discussed in Congress deal with 1) banking reform, 2) energy and environment, 3) health care or 4) unemployment?

The overall news IQ was pretty low. The answers to this question, though, were near the lowest of the low. Only 23 percent of those who took the quiz chose the correct answer, which is No. 2, energy and the environment.

To be sure, reasonable people could disagree with cap-and-trade proposals circulating on Capitol Hill. That question wasn’t asked. Busy people also could be forgiven for not knowing the considerable intricacies of those proposals. But not knowing so much as their general gist?  

Something other than scientific argument and news coverage of the public policy issues is turning public opinion to quite a remarkable degree.

Any clues anyone?