New York Times: With the scientific consensus more or less settled that human activity – the burning of fossil fuels, torching of forests, and so forth – is contributing to a warmer and less hospitable planet, one might reasonably ask, why is it so hard to agree on a plan to curb those activities? The answer lies with the many fault lines that cut through the debate over climate change. Those deep divisions will be on display beginning this week as representatives of 192 nations gather in Copenhagen …