The climate changes under discussion mostly are gradual, occurring over a timeline of generations - 50 years, 100 years or more. Consequently, the argument by climate skeptics that humanity will have time to adapt - perhaps even adapt easily - is difficult to disprove.

Likewise, the counter argument - that although humanity may be able to adapt, animals and plants may not - remains to be seen.

In any case, the factions probably will have to hand off their "I-told-you-sos" to subsequent generations, because the people on the winning side will not be around to gloat themselves.

Nonetheless, there are compelling reasons to pay attention to the discussion. The first simply is because it is interesting. Climatology and meteorology are young sciences - brand new, practically.

They have made great strides in the last 50 years. Anyone who doubts this should consider the haphazard weather forecasts of 30 or 40 years ago to the remarkably accurate long-term predictions routinely issued nowadays.

Climate science and climate modeling report important new findings with a regularity that is exhilarating. It was not very long ago that no one had ever heard of El Nino, or the North Atlantic oscillation or thermohaline circulation. Now, much of it is the stuff of everyday conversation among educated laypeople.

A more critical reason to pay attention is that nations have to decide what, if anything, to do to deal potentially destructive changes. Some argue to invest now to cut off greenhouse-gas emissions at the source, thereby reducing future impacts, Others counter that the money is better spent fashioning adaptations to a warmer world.

Even if the skeptics are correct - and humans can easily adapt to global warming - those adaptations are going to cost money.

Climate science actually is challenging the conventional way of thinking about investing in the future - something economists, the guardians of thought about long-term money, are loath to admit.

Applying traditional economic tools, such as the discount rate, to investing in the amelioration of global warming, you quickly discover that you cannot justify even a tiny investment to stop or slow it.

At a 10 percent discount rate - a common figure used in loans to developing countries, for instance - damages of $25 trillion some 200 years hence, approximately equal to today's entire global GDP, have a present value of only $132,000.

Put another way, a $132,000 investment in climate today could prevent $25 trillion damages to our descendants 200 years from now.

That kind of thinking clearly is indefensible.

"If I plant a bomb to go off in Manhattan in 500 years, if we discount that from the present, the discount rate tells us that there is no damage. That can't be right," Dale Jamieson, a professor of environmental studies and philosophy at New York University, told UPI's Climate last summer.

"The unfortunate reality of the discount rate is that if you use any discount rate that makes sense in the short term, it turns out that in the long term, the world isn't worth saving," said Irving Mintzer, a senior associate of the Pacific Institute for Studies in Development, Environment and Security.

Carried to its logical extreme, it means our lives are worth everything, but our grandchildren's lives are worth nothing. Mintzer said, "Even if it rational to think that your children should have a world to live in, it is probably not rational to think that your grandchildren should have a place to live in. That turns out to be not an especially informative insight."

Modern societies, and capitalist societies in particular, are not very good at valuing the long-term. Climate science, with its very long-term outlook, continually points out that failing.

Two recent articles illustrate how long climate issues are likely to be with us. The first, in last week's issue of the journal Science, found the planet is committed to a considerable amount of warming for the next 100 years, even if greenhouse-gas emissions are capped immediately.

The article's author, Gerald Meehl, a climate scientist with the National Center for Atmospheric Research in Boulder, said if emissions had been capped at 2000 levels, sea level would continue to rise an average of about 4 inches (11 centimeters) by 2100 because of thermal expansion of seawater.

"The main idea is that the sea-level rise, in terms of the commitment we have already made, is greater than the temperature," Meehl told Climate. "The ocean keeps expanding. It takes 50 years years to warm the lower depths. Sea-level rise is more sustained and over a longer period than temperature."

The longer we wait to do anything, he added, "the worse the problem gets."

Meehl's results include only sea-level rise from thermal expansion, but when melting glaciers and ice caps are included in the calculations, the estimates can double.

The second article, on the Web site RealClimate.org, found that the physical processes around the life cycle of human-generated carbon dioxide figure to keep it in the atmosphere for a long, long time.

The author, David Archer, a professor of geosciences at the University of Chicago, wrote: "I calculate a mean lifetime, from the sum of all the processes, of about 30,000 years.

That's a deceptive number, because it is so strongly influenced by the immense longevity of that long tail.

If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes."

That long tail "is a lot of baby to throw out in the name of bath-time simplicity," Archer continued. "Major ice sheets, in particular in Greenland, ocean methane ... deposits, and future evolution of glacial/interglacial cycles might be affected by that long tail.

"A better shorthand for public discussion might be that CO2 sticks around for hundreds of years, plus 25 percent that sticks around forever."

If you apply a 10 percent discount rate to 25 percent of forever, you get ... oh, never mind. Journalists are notoriously terrible at math.

Climate is a weekly series examining the potential impact of global climate change, by environmental reporter Dan Whipple.

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