New York Times: Every day, the critical December summit in Copenhagen grows closer. All agree that climate change is an existential threat to humankind. Yet agreement on what to do still eludes us. How can this be? The issues are complex, affecting everything from national economies to individual lifestyles. They involve political trade-offs and commitments of resources no leader can undertake lightly. We could see all that at recent climate negotiations in Bangkok. Where we needed progress, we saw …