On climate change, the politics are bitterly frozen

The fifth report of the Intergovernmental Panel on Climate Change (IPCC) has provided undeniable proof of a remarkable phenomenon: a public debate even more bitter and polarized than the budget showdown.

The intersection of science and policy, of climate and politics, has become a bloody crossroads. Blog-based arguments over ocean temperatures and the thickness of the Greenland ice sheet are as shrill and personal as any Tea Party primary challenge. And the IPCC report — designed to describe areas of scientific consensus — has become an occasion for polarization.

Environmental advocates have done their side no favors. The most eager have been caught in a sleight of hand. In the past, they have used relatively brief periods of warming and short-term weather patterns to bolster their arguments about climate disruption — a tactic that has come back to bite them in the El Niño.

Recent warming has been slower than the long-term trend — what has been called a "hiatus." Time scales that environmental advocates once touted as significant are now dismissed as irrelevant. Skeptics have cried gotcha.

In fact, the 15-year warming hiatus is both misleading and pretty much irrelevant. Short-term trends can be exaggerated by the choice of a statistical starting point. The year 1998 was particularly hot. A graph beginning in 2000 would yield a different slope. And the occasional flattening of temperature rises is exactly what you'd expect in climate science, which assumes bumps upward and downward along a generally rising curve.

However the IPCC report is used or abused, it represents a consensus and not a conspiracy. "Each of the last three decades," it concludes, "has been successively warmer at the Earth's surface than any preceding decade since 1850." The oceans have warmed and grown more acidic. Ice sheets are losing mass. Sea ice and snow cover in the Northern Hemisphere are shrinking. Ocean levels are rising.

All these things are plausibly related to increased atmospheric concentrations of greenhouse gases produced in vast amounts by humans. And these trends involve serious public risks.

The main problem in dealing with climate change is not scientific uncertainty. It is the inability of political systems to deal with a certain type of risk and reward.

First, in this case, the geographic distribution of risk is unequal. Southern England might eventually have the growing seasons of France. Parts of Africa might see advancing deserts. And while New York City and Bangladesh might both be vulnerable to rising sea levels, only one will have the resources to adapt to change.

Second, the temporal distribution of rewards is unfavorable. Resources expended today will only get limited results well into the future. Because the cumulative production of carbon is the problem, many of the changes we are seeing are essentially irrevocable. "Most aspects of climate change," says the IPCC report, "will persist for many centuries even if emissions of CO2 are stopped."

This does not mean that restricting greenhouse gas emissions is useless, just that it is politically thankless. Inaction may have terrible results. Even vigorous action, however, would only start limiting the terrible results at some point in the middle of the century. And it would never undo them.

We could leave most of the vast reserves of fossil fuels in the ground — a political and economic impossibility — and still the ice would melt and the sea would rise. It is no wonder that even politicians who believe in warming tend to have other priorities.