The evidence was strong 10 years ago, even 20, that the world had a problem with global warming. We knew then that it was going to exacerbate extreme weather and heat waves and raise the sea level. But nearly half of Americans didn't take it seriously. Now they do, according to polls, and what changed wasn't the amount of evidence but a shift in political forces and some changes in the way scientists learned to make their case.
A recent report on cumulative damage to the world's oceans and ice caps, for example, got big attention in the media, though the message wasn't all that different from earlier reports from the Intergovernmental Panel on Climate Change. A few more specifics are known: The report projects that by 2050, at many coastal locations, the historic once-in-a-century flood will become an annual event, said Princeton University climate researcher Michael Oppenheimer, who was an author of the report.
What's noticeably changed is the way Americans are reacting to the news — taking these forecasts seriously, and recognizing that this isn't only about polar bears, but about them. One clue to America's new attitude comes from tracking polling data over the years, said Yale professor Anthony Leiserowitz, who studies public opinion on climate change. What the data show is a steep 14 percent drop in public acceptance of human-caused global warming between 2008 and 2009.