Melting glaciers, rising sea levels, fires, floods and droughts. On the eve of a historic election, award-winning producer and correspondent Martin Smith investigates how the world's largest corporations and governments are responding to Earth's looming environmental disaster.

"I have reported on the Cold War, the breakup of the Soviet Union, the rise of Al Qaeda, and the wars in Iraq and Afghanistan," says Smith. "But nothing matches climate change in scope and severity."

The world needs to dramatically cut the carbon emissions responsible for wreaking havoc on the planet's climate, according to Dr. Rajendra Pachauri, whose organization, the Intergovernmental Panel on Climate Change (IPCC), shared last year's Nobel Peace Prize. "If we don't take action immediately, we face a crisis," Pachauri tells Smith. "Climate change is caused by human actions, and we need to do something about it. The sooner we realize that, the better."

With that sense of urgency in mind, Smith traveled to 12 countries on four continents to investigate whether major corporations and governments are up to the challenge. HEAT features in-depth interviews with top policy-makers and with leading executives from many of the largest carbon emitters from around the world, including Chinese coal companies, Indian SUV makers and American oil giants. The report paints an ominous portrait. Despite increasing talk about "going green," across the planet, environmental concerns are still taking a back seat to shorter-term economic interests.

Smith's journey begins at the epicenter of new industrial development: China. In the midst of unprecedented growth, the Chinese are clearly moving in the wrong direction. He visits Shenhua Energy, one of the largest and fastest-growing power companies in the world -- a coal conglomerate with a huge carbon footprint. But its CEO, Dr. Ling Wen, tells Smith that he answers not to the public but to his shareholders. "We must create money, not lose the money," Ling says. "It's my responsibility as a CEO of this company." And when pressed whether he should make climate change a higher priority, Ling says that he would if his shareholders asked him. But, he says, "I'm afraid maybe all the shareholders, they cannot accept that concept." In the meantime, China continues to build two new coal-fired power plants every week.

Smith finds a similar situation in India, where rapidly rising income levels have prompted an explosion in the demand for new cars. Automakers are thriving, pushing out new models, including the Nano, a small car aimed at helping even the poorest citizens get behind the wheel -- no small thing, as India stands to overtake China as the world's most populous country by mid-century. With several hundred million new drivers taking to the streets, India's carbon emissions will soar.

And with new cars, of course, come new roads, linking crowded cities and fueling a construction boom across the developing world that drives emissions ever higher. The manufacture of cement is the third-largest industrial contributor of greenhouse gases in the world. Supplying more cement for buildings, roads and bridges makes big emission reductions impossible. This presents a core dilemma for all large emerging nations, from China to India, Indonesia, Russia, Mexico and Brazil: how to grow without inflicting more damage on the environment.

"I think the difficulty we have is that countries that have developed and have done the polluting part are now asking the countries that are developing, 'OK, you can't pollute,'" says Hameed Bhombal, of Aditya Birla Group, an Indian megaconglomerate. "It has to be done in a way that's fair."

According to Dr. Pachauri of the IPCC, the onus is on the developed world to lead the way. Now, with the rise in gas prices, there is an additional incentive for American car companies to offer smaller, more efficient vehicles. But will they respond? Their record is discouraging. Smith asks Beth Lowery, head of environmental affairs at General Motors, why Toyota beat GM to the Prius. Lowery replies that GM looked at hybrids from a "business case" and asked, "Can this vehicle make money?" GM banked instead on trucks and SUVs and is now suffering its worst performance in 50 years. GM is now playing catch-up and investing billions in a new hybrid, the Chevy Volt, which is scheduled to be released in 2010.

While hybrid cars may emit less CO2 than their gas-guzzling cousins, they still require electricity to run. Making cars like the Volt part of a campaign to seriously reduce emissions will mean finding a new, cleaner power source. Currently, more than half of American power comes from coal. Coal is cheap and reliable, but dirty.

The answer, the industry says, will be "clean coal" -- a complex process by which the burnt-off carbon will be captured and buried in the earth's crust. But as Smith investigates, he finds there are serious doubts about whether "clean coal" will ever work. When pressed, utility CEO David Ratcliffe of Southern Company, one of the world's largest emitters of greenhouse gases, concedes that "we haven't even come close to defining what are the legal liabilities and what are the permitting requirements" for removing carbon from coal and burying it underground. Recently, several "clean coal" projects in the U.S. have stalled over these and other uncertainties. As Jeffrey Ball, environmental news editor at The Wall Street Journal, tells Smith, "There was huge, rosy optimism about it. What's wrong is that reality is intruding."

On the campaign trail, both Sen. John McCain and Sen. Barack Obama have announced their plans for a new energy policy that will cut carbon emissions. Optimistically, they suggest that the "greening" of American business heralds a new era of sleek technologies and opportunities for innovation. What they tend not to emphasize is cost and, on the part of every consumer, sacrifice.

In his interview with FRONTLINE, California's attorney general, Jerry Brown, reminds Smith that it won't be easy: "Our wealth, our society, our being is driven by oil and carbon. It's intellectually dishonest to somehow say we can get some light bulbs or get a Prius, and then we're all done. No, this is going to take massive technological innovation. It's going to take changes in the way we live and work. And it's going to take cooperation of unprecedented degrees among business and government and among countries. That's where we are, and that's why there's no other word except 'daunting.' I'm hopeful. I'm cautiously optimistic. But I would have to say one has to approach this with great humility."

Author and journalist Jeff Goodell adds: "We seem incapable of grasping what's at stake here, perhaps because so much is at stake. Addressing this really means reinventing the engine of our lives -- which is fossil fuels."