Another report has highlighted evidence of the serious, long-term consequences of global warming. Yet governments continue to pay only lip service to the threat. As the new study makes clear, the cost of environmental destruction will be severe — but there is still time to avoid the worst impacts, if the world takes immediate and cooperative action.

The latest warning is from former World Bank chief economist Nicholas Stern, who was tasked by Britain’s Chancellor of the Exchequer with providing an independent assessment of the economics of climate change. His conclusions are striking and simple. First, “the scientific evidence points to increasing risks of serious, irreversible impacts from climate change associated with business-as-usual paths for emissions.”

The current level of greenhouse gases is nearly twice the level that existed before the Industrial Revolution, and the annual emissions rate is accelerating. As a result, there is at least a 77 percent chance — “and perhaps up to a 99 percent chance” — of a global average temperature rise exceeding 2 C. There is at least a 50 percent risk that temperature change will exceed 5 C.

Second, the impact of these changes — even at the lower end of the scale — will be severe. The report notes one-sixth of the world’s population will experience water shortages; tens, perhaps hundreds, of millions of others will be threatened by rising sea levels. As much as 15 to 40 percent of species will be threatened with extinction. Humanity will not be threatened as a whole, but entire regions will be hard hit. Africa could lose one-third of its crop yield and there could be a 25 to 60 percent rise in hunger worldwide. At the high end of the spectrum, even developed countries will lose fertile lands. The Stern report estimates that the economic damage wrought by climate change could equal that caused by the Great Depression or a world war — 5 to 20 percent of global gross domestic product.

The third conclusion is the most alarming: There is a window of opportunity to halt this disaster, but action must be taken quickly. The effect of climate change is cumulative: As Mr. Stern succinctly explains, “the sting is in the tail.”

What is most disturbing about this conclusion is Mr. Stern’s estimate that the cost of stabilizing greenhouse gas emissions is not that high: He reckons it will be about 1 percent of GDP by 2050. But that is only if we act fast. Waiting a decade or two would make it impossible to stabilize emissions at a lower level and significantly increase the costs of mitigating the negative effects of climate change.

Contrary to popular wisdom, moving to a greener economy need not be drag on economic growth. In fact, the cost of mitigation is likely to be considerably less than the amount that would be spent on the consequences of climate change.

The Stern report notes that the market for low-carbon energy products could be worth $500 billion a year by 2050. And governments already spend about $250 billion annually on energy subsidies that can be rejiggered to promote greener alternatives — or eliminated altogether.

As one environmental advocate noted, it isn’t that taking action on global warming will hurt the economy: “just the opposite is true — it’s the refusal to take serious action that poses the true risk to our future economic prosperity.”

The search for more efficient energy sources and related technologies — such as storage cells — plays to Japan’s strength. According to the International Energy Agency, Japan is the only developed economy that has increased spending on research in energy efficiency and solar technology in recent decades. Most countries are cutting such expenditures.

That has to stop. British Prime Minister Tony Blair’s acknowledgment that the Stern report is “the most important report on the future to be released by this government” is a first step. Without concerted pressure on all governments and all sectors of society, business as usual will prevail.

The holdouts — among them U.S. President George W. Bush — will continue to insist that the current effort is adequate, given the uncertainties and the potential downside. They have already dismissed the Stern report as just another study that does not add to our understanding of the problem.

The Stern report is much more than that. It is a measured assessment of the risks of climate change and the rewards that will follow from concerted action. It provides a rallying point for action that is the only way to offset impending climate change. And, quite simply, it uses self-interest as motivation. The choices are becoming clearer. Future generations will know whom to blame if we do not take action now.

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