If the world keeps getting hotter, people aren't likely to take it lying down. If water is scarce, if food is scarce, if land is scarce (because of a rising sea level), families and tribes and nations are sure to fight for what resources they can get. Or they'll try to move to other parts of the world where conditions are better - those parts in general being in North America and Europe.
In short, climate change will brew conflict.
This week, a group of retired American admirals and generals issued a report pointing out that global warming is going to be a military issue. Two regions that are probably going to feel its brunt are the Middle East and Central Asia (where snow melt from diminishing Himalayan glaciers is a main source of water). Both are fonts of Islamist, anti-Western jihad; worsening conditions aren't likely to ameliorate the appeal of violent ideology.
Sub-Saharan Africa stands to lose, too, as agriculture becomes more marginal.
A few of the retired officers who took part in drawing up the report, and who testified yesterday before a House panel, say they were skeptical that global warming was a problem until they began looking into its consequences. Now they warn that it will have tremendous security implications for the United States.
One point they didn't raise is that Russia could gain with a warmer climate, which would pose a challenge of a different sort, but probably no less real. In fact, the U.S. Navy has begun preliminary planning for operations in an ice-free Arctic.
The U.N. Security Council took up the issue of global warming for the first time Tuesday, prodded by the United Kingdom. "The implications of climate change for our security are more fundamental and more comprehensive than any single conflict," said Britain's foreign secretary, Margaret Beckett.
She pointed out that the deepening drought in Sudan may well be a factor in the conflict in Darfur, which at its root pits herders against farmers, and which has killed hundreds of thousands and displaced 2.5 million since it began. It's a glimpse of what could be much more to come.
The report by the generals and admirals called for a "greener" military, one that wouldn't be so dependent on oil and the long supply trains needed to deliver it. But the real implication in all this is that there still might be time to head off the most devastating results of climate change, and that even the rich countries of Europe and America would be well-advised to do what they can. Thirst and hunger are powerful motivators, and trying to hog precious resources could prove to be expensive, hazardous - and ultimately futile.