One would think that by now most people would have figured out that climate change represents a grave threat to the planet. One would also have expected from Congress a plausible strategy for reducing the greenhouse gas emissions that lie at the root of the problem.

That has not happened. The House has passed a climate bill that is not as strong as needed, but is a start. There are doubts about whether the Senate will pass any bill, given the reflexive opposition of most Republicans and unfounded fears among many Democrats that rising energy costs will cripple local industries.

The problem, when it comes to motivating politicians, is that the dangers from global warming  drought, famine, rising seas  appear to be decades off. But the only way to prevent them is with sacrifices in the here and now: with smaller cars, bigger investments in new energy sources, higher electricity bills that will inevitably result once we put a price on carbon.

Mainstream scientists warn that the longer the world waits, the sooner it will reach a tipping point beyond which even draconian measures may not be enough. Under one scenario, atmospheric concentrations of greenhouse gases, now about 380 parts per million, should not be allowed to exceed 450 parts per million. But keeping emissions below that threshold will require stabilizing them by 2015 or 2020, and actually reducing them by at least 60 percent by 2050.