Two sets of headlines on global warming converged early last week, one dealing with the future and one with the past, and the upshot was especially discouraging.

In London, a former World Bank president issued a 700-page report suggesting that the price of averting catastrophe might be 1 percent of the globe's gross domestic product for the next half-century — and that was the good news. The cost of failing to throttle back on greenhouse gases, Sir Nicholas Stern calculated, would fall somewhere between 5 percent and 20 percent, enough to create a worldwide equivalent of the Great Depression.

Meanwhile, the New York Times reported that federal spending on energy research has fallen to about half the levels of 1980, after adjustments for inflation. This is not just an American problem; among the world's other industrial powers, only Japan keeps raising its spending on research into future energy technologies.

One percent of global gross domestic product may sound like a lot, and in fact it is in the neighborhood of a half-trillion bucks. But there's a matter of perspective; overall, military spending worldwide consumes 2.5 percent (here the United States is well above average at 3.7 percent).

And, as the Stern report underlines with elegant simplicity, it really is just a question of whether we pay a lot now or a lot more later — and of what we get for the money.

For the 1 percent investment, we get nonpolluting, perpetually renewing power from the sun and wind in place of our smoggy infrastructures powered by burning coal, oil and, in stunningly large parts of the developing world, wood. For the larger investments, we get the costs of coping with refugees in the hundreds of millions in flight from coastal flooding, droughts, famines and pandemic disease.

For the 1 percent investment, the world's industrialized nations might also divvy up an annual savings in energy costs of well over $2 trillion a year. Poorer nations would measure their share of the payback in lives not lost and lands not abandoned.

For all the imprecision of their figures, Sir Nicholas and his colleagues have solidly countered the Bush administration's key arguments on global warming — that joining Britain, Canada and other industrial leaders in sharply cutting carbon emissions would bring economic ruin, and that there's plenty of time to figure out the best responses.

The truth is exactly opposite. The problem has grown only more urgent since President Bush took office and immediately reversed his promise to throttle back U.S. carbon emissions, and the costs of inaction are growing larger still. With each passing year, the cost of each unspent dollar shifts toward the $20 end of the spectrum.

Still, the Stern report is optimistic about the potential of urgent and concerted worldwide action, in part because of technological progress on capturing carbon and making clean electricity. That requires U.S. leadership in two forms: making a serious cut in our 25 percent share of the world's emissions, and demonstrating a concern that extends beyond our short-term economic pain.