As we near the end of this scorching summer, a reasonable person can't help wondering whether the drought and shimmering heat we've been experiencing are a preview of what's ahead if global warming continues.

The problem, of course, is that a reasonable person can't be certain about global warming. The scientific data are still tentative; meanwhile, a powerful political lobby denies that any real problem exists. So there's an inevitable tendency to sit back in the hammock and take one more leisurely swing before summer's end.

But let's assume, for the moment, that the worriers are right. Let's assume that a relationship exists between the measurable increase in greenhouse gases in the atmosphere and the measurable warming of our planet by about one degree Fahrenheit over the past century.

And let's assume, finally, that the link between these greenhouse gas emissions and global warming, while hard to prove now, will turn out to be as strong as the link between cigarette smoking and poor health.

Right now, the global-warming debate bears an eerie resemblance to the smoking debate several decades ago. Back then, smokers might have been wheezing and coughing, but the tobacco companies were still running ads featuring respectable looking doctors who assured the public that cigarettes didn't do any real harm.

A current version of this upbeat science is the argument put forward by one pro-industry group, the Competitive Enterprise Institute, that more carbon dioxide in the atmosphere may actually be good for plants. Plants need the stuff to survive, after all, and the institute's newsletter, "Cooler Heads," contends: "Trees do better with more CO 2 ."

I hope they're right. Just as 20 years ago, puffing away happily on yet another Marlboro, I hoped the hacking cough I seemed to have each morning was just a persistent cold.

As with tobacco, there are powerful economic interests that would be harmed if we ever decided to take global warming seriously. For generations, members of Congress invoked all those poor tobacco farmers to explain why they wouldn't take tough action against smoking. But when it comes to global warming, we're all tobacco farmers. We've built an entire economy that lives off carbon-dioxide emissions. There are the oil companies that produce the hydrocarbons, and the car companies and electrical utilities that burn them.

So it's no surprise that Congress is siding with industry in opposing any action to reduce global warming, just as it sided for so many years with the tobacco companies.

But suppose the doomsayers are right. Imagine what the world might look like 50 years from now if global warming continues. That's precisely the task that has been undertaken by the government's U.S. Global Change Research Program, in its "national assessment" of global climate change. I recently had a chance to review an early draft of the group's report, "Preparing for a Changing Climate," which is to be released in January.

If you're looking for a scary Labor Day beach book, this is it. It's still a draft, so the conclusions aren't final. But here are some of the changes that seem likely as the world gets hotter and variations in global climate become more extreme:

In the Northeast, warmer summertime temperatures and moister air are likely to raise the heat index, making city life less comfortable. Along the Atlantic coast, development may be threatened by more hurricanes and rising sea levels. In the Appalachians, warmer and moister air may lead to more intense rains and flash floods.

In the Southeast, forests and agriculture may be affected by rising temperatures. Along the Gulf Coast, inundation of coastal wetlands may increase.

In the West and Southwest, warmer winter temperatures may change the pattern of snow melting -- causing more runoff in winter and less in summer. That, in turn, would increase the threat of mudslides in winter and fires and water shortages in summer.

For the moment, these predictions are educated guesses -- based on the best computer modeling that's available but by no means established fact. And that will give wiggle room to all the skeptics and naysayers who will surface when the final report is published early next year.

But let's suppose that the assessment is right and we've got a hotter, wetter world -- with more of the extreme weather we've seen the past few years. What will people say, looking back at 1999? Whom will they blame? And to take the kind of practical problem lawyers enjoy, who will pay the cost?

Here again, the best analogy may be tobacco. If global warming predictions prove accurate, the companies that have been working so hard to deny them may have a problem. Indeed, they may even have legal liability. And in a world where rising seas are inundating Miami and mudslides are devastating Los Angeles, the potential liability could total trillions of dollars.

Lynn Coleman, a former deputy secretary of energy who does legal work for some of the big oil companies, warns that the industry shouldn't ignore the risk of this sort of litigation. Energy may not turn out to be very different from tobacco or guns, he says.

If it can be shown that energy companies were selling products despite evidence that they might cause harm, Coleman notes, there may be a cause of action for what lawyers call a "tort." By one estimate, the insurance industry has begun creating a $200 billion reserve to pay the costs of damage caused by hurricanes and other extreme weather events. Someone is going to pay that bill.

Global warming, in this sense, may be a plaintiff lawyer's dream. And it's interesting, in a perverse way, to imagine how a jury in 2050 might react to some of the recent industry-backed studies minimizing the dangers of global warming. I suspect future jurors will not be amused.