When Congress last pushed for comprehensive climate legislation a decade ago, much of corporate America was either neutral or hostile. In a sign of how much corporate attitudes have changed, the Business Roundtable, one of the country’s most prominent business groups, is throwing its support behind broad-based measures to slash greenhouse gas (GHG) emissions. In a statement of principles released Wednesday, the Business Roundtable said it “supports a goal of reducing net U.S. GHG emissions by at least 80% from 2005 levels…