It's not in Al Gore's PowerPoint presentation, but there are some upsides to global warming.

Northern homes could save on heating fuel. Rust Belt cities might stop losing snowbirds to the South. Canadian farmers could harvest bumper crops.

Greenland may become awash in cod and oil riches. Shippers could count on an Arctic shortcut between the Atlantic and Pacific. Forests may expand. Mongolia could see a go-go economy.

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This is all speculative, even a little facetious, and any gains are not likely to make up for predicted frightening upheavals elsewhere.

But still — might there be a silver lining for the frigid regions of Canada and Russia?

"It's not that there won't be bad things happening in those countries. There will be — things like you'll lose polar bears," said economic professor Robert O. Mendelsohn of the Yale School of Forestry & Environmental Studies. "But the idea is that they will get such large gains, especially in agriculture, that they will be bigger than the losses."

Mendelsohn looked at how gross domestic product around the world would be affected under different warming scenarios though 2100. Canada and Russia tend to come out as gainers, as does much of northern Europe and Mongolia.

This is largely because of projected gains in agricultural production in those areas. Many researchers believe that if the world warms up, the sweet spots for growing crops will migrate toward the poles.

Some people claim the phenomenon is already manifesting itself in bountiful forsythia blooms in Vermont and maple sap flowing in upstate New York in January.

"I've been betting on it for years," said Chris Loken, a Hudson Valley apple grower who years ago diversified his LoveApple Farm with an eye toward warmer weather.

Amid acres of apple trees lined up along bucolic hills in Ghent, N.Y., Loken planted stands of peach, apricot and plum.

Frosty upstate New York winters are not always kind to those trees, but the 75-year-old farmer is counting on a trend of milder winters.

"This farm here has been set up for the future," he said.

The future may have arrived already in icy Greenland, where fishermen are thrilled by the return of cod and farmers are reporting higher yields.

"Maybe the turnips get a little bit bigger, and the potatoes get a little bit bigger, but that's important," said Kenneth Hoegh, a government agricultural adviser. "We are right on the edge here for agriculture."

Jesper Madsen, who directs Arctic research at the National Environmental Research Institute in Denmark, said Greenland's agricultural gains would seem like small potatoes economically if the retreating ice there clears the way for more oil drilling.

Still, people shouldn't start planting banana trees in Boise or book a beach vacation in Iceland just yet. A likely warm-up would be gradual and might even be mitigated if the world cuts greenhouse gas emissions.

Currently, the "optimal holiday destination" has an annual average temperature of about 61 degrees (think Atlanta, or Barcelona), according to a group of European researchers.

A worldwide warming will essentially drive tourists away from equatorial regions toward the poles and up the mountains, said one of those researchers, economist Richard Tol of the Economic and Social Research Institute in Ireland.

So ... surf's up, Buffalo?

Probably not. While oceanfront cities might have to build seawalls to hold back the ocean in a warming world, some researchers believe the freshwater Great Lakes will evaporate a bit.

But a projected 11-degree boost by the turn of the next century could be a boon for chillier cities like Cleveland, Milwaukee, Detroit and Buffalo, even knocking them into the "optimal" holiday range.

"A shorter winter with less snow might help counter Buffalo's inaccurate reputation as snow capital of the East Coast," said Marti Gorman, a local booster.

Looking around the world, a list provided by Tol said the biggest winner in a warmed-up world would be — no surprise — Canada.

It would see a 220 percent increase in international tourist arrivals by the end of the century, followed by Russia with a 174 percent jump, and Mongolia, up 122 percent.

Of course, the caveats are significant when trying to make any long-term global forecast. There are so many variables.

A longer growing season does a farmer no good if resulting rain patterns bring a drought. Mendelsohn said northern residents saving on winter heating fuel will end up spending more than that to keep cool in the summer.

Great Lakes cities might enjoy balmier weather, but could suffer if lower lake levels cut off shipping lanes. And global warming could present deadly new opportunities for parasites and disease.

Some researchers stress that there aren't really any winners in global warming because the planet as a whole will be such a big loser.

Marginal gains in limited areas can't be stacked up on one side of the ledger, they say, when the negatives can include planet-wide food and water shortages, mass flooding and extinction.

"In the end, you don't find really large, really significant benefits," said Michael MacCracken, chief scientist at the nonpartisan Climate Institute in Washington. "I mean, loss of biodiversity is an irreversible thing for the planet. Saving a little money on heating in winter areas is a small economic gain for some people. How do you compare that?"