Associated Press: As Congress begins to debate climate change in earnest, the science is taking a back seat to economics: How much will it cost to slow the Earth’s warming because of man-made pollution — and what’s the cost of doing nothing? With a key House committee starting four days of hearings, Speaker Nancy Pelosi, D-Calif., vowed to get a climate bill approved this year. Noting that Earth Day will be celebrated on Wednesday, she told reporters by the next Earth Day “we want to celebrate what …