Global warming is a complex issue to figure out, but one thing about it is actually quite simple -- discerning which side dominates the debate right now. For the past year, those who view global warming as a crisis justifying a major federal response have had just about everything going in their favor.

Granted, the Bush administration continues to resist first-ever mandatory limits on carbon-dioxide emissions from fossil fuels, but the Democratically controlled Congress has introduced a number of so-called cap-and-trade bills to do just that. Some of them have bipartisan support. And many of the leading presidential candidates have endorsed these efforts.

Several other factors, including a recent Supreme Court decision compelling the Environmental Protection Agency to consider global warming measures, as well as state and local efforts to bypass the feds and impose their own controls, all seem to be forcing Washington's hand.

Meanwhile, the opposition to cap and trade seems to be collapsing. The owners of the nation's coal-fired power plants, manufacturing facilities, and oil companies -- until recently the most politically powerful holdouts -- have largely given up the fight. Most now see some form of fossil-fuel rationing as inevitable, and several are actually lobbying for cap-and-trade legislation in the hope that they can shape it to their advantage.

Of course, the driving force behind all of this is the steady stream of gloomy claims about global warming. Most recently, the U.N. Intergovernmental Panel on Climate Change (IPCC) report received widespread coverage as the smoking-gun evidence that mankind is warming the planet to dangerously high levels. Al Gore's Academy Award-winning movie and accompanying bestseller, An Inconvenient Truth, has also done much to hammer home the message.

The drumbeat continues as virtually every natural disaster that occurs-- from storms, to droughts, to floods, to wildfires, to disease outbreaks-- gets pinned on global warming. Even normal summer temperatures sometimes get alarmist ink.

The frightening coverage has clearly shaped public opinion. Surveys consistently show that a majority of Americans want their government to do something about warming.

Taking all of this into account, there's no question that global-warming activists currently have the momentum. But momentum can change, and on this issue there are reasons to believe it soon will. It may well be that the prospects for the cap-and-trade bills are peaking -- before being enacted into law -- and will begin to fall once as the following factors come into focus.

China's Great Leap Forward on Emissions.
A central part of the climate-change message has been the demonization of America as the world's top global-warming culprit. But that will soon change, as China is close to surpassing the U.S. and becoming the biggest emitter of greenhouse gasses. When this shift happens it will have tremendous practical as well as symbolic significance, and it will dim the appeal of unilateral U.S. action.

It is important to note that China isn't slowly edging past America; it is roaring ahead. Emissions of carbon dioxide, the byproduct of fossil-fuel combustion and the greenhouse gas of greatest concern, are exploding along with China's economy. New coal-fired power plants are reportedly being added in China at the rate of about one per week, and these facilities are less efficient and higher-emitting than their western counterparts. According to the Netherlands Environmental Assessment Agency, which believes China has already surpassed America, emissions in China rose 9-percent in 2006, on top of a 12-percent increase in 2005. Meanwhile, America's emissions have been growing much more slowly, averaging little more than 1-percent per year. They actually declined by 1.3-percent in 2006, according to the Department of Energy.

The U.S. was easily the biggest emitter during the 20th century, but future carbon-dioxide emissions will come less from American sources, and more from Chinese ones. Even if the U.S. saddled itself with economy-damaging energy constraints, it would barely begin to offset China's projected increases. But so far, China has adamantly refused to agree to any controls, arguing that economic growth is their top priority. Other fast-growing developing nations have said the same thing.

Thus, notwithstanding questions about the seriousness of the global-warming problem, any bills that single out U.S. emissions will be a fast-shrinking part of the solution. As China's emissions race ahead of ours, Americans will begin to realize that unilateral action is not the way to go.

The Failing Kyoto Protocol
The 1997 Kyoto Protocol, the multilateral global-warming treaty, is still being touted as a great success. The Western European governments that signed onto the treaty continue to congratulate themselves for doing so while criticizing America for staying out. Most climate activists here convey the same message. They hope to convince Washington to make up for lost time by enacting one of the Kyoto-like cap-and-trade bills currently under consideration.

But far from being a model to emulate, Kyoto is proving to be a near-complete failure, and over time it is going to get more difficult to conceal this fact.

For all their rhetoric, the European nations are well off track of Kyoto's requirement that emissions be 8-percent below 1990 levels starting in 2008. Official European emissions data shows that nearly every one of these countries has higher carbon-dioxide emissions today than when the treaty was signed in 1997, and the emissions increases show no signs of leveling off. The same is true of Canada, Japan, and other major non-European signatories. In fact, most of these countries are seeing their emissions rising faster than those in the U.S.

Pro-Kyoto Protocol activists and the media continue to heap praise on the treaty for its carbon-emissions goals, but they rarely explore the obvious question of whether these goals are actually being met. But the failure to reduce emissions can't remain a secret for much longer. Once Kyoto reality sets in, it will deal a blow both to the treaty itself and to any congressional efforts to mimic its approach.

The High Costs to Cool The Planet
The reason Kyoto Protocol signatories are not reducing their emissions is that doing so is proving to be prohibitively costly. These nations are learning the hard way what the Bush administration has understood all along -- that attempts to rapidly force down the fossil-fuel use that provides the backbone of modern economies will be very expensive. As costs enter into the debate, they could well prove to be a game changer.

While inundating the public with scary stories about global warming's effects, the proponents of cap-and-trade have thus far said little about the costs of combating the threat--and for good reasons. Their agenda would inflict serious and noticeable economic pain long before it would have even a modest impact on the earth's future temperature. Kyoto's provisions, if fully implemented, would have cost Americans hundreds of billions of dollars annually from higher energy prices, but would, according to proponents, avert only 0.07 degrees Celsius of global warming by 2050.

Given the Kyoto Protocol's small impact on warming, many proponents believe that the treaty should be just a first step towards much stronger controls. But, as the European experience is showing, even this first step is proving too costly and impractical.

It should be noted that the surveys indicating public support for action on warming also show that the support quickly turns into opposition if the measures taken would raise energy prices appreciably. This is especially true for gasoline prices, and on this point the European experience is worth noting. A European Environment Agency report found that greenhouse-gas emissions from motor vehicles continue to rise due to increased driving, despite punitively high European gasoline taxes that push the overall price well above $6 per gallon. In fact, increased vehicle emissions are a big part of the reason most Western European countries are going to miss their Kyoto targets. If $6 per gallon is not high enough to discourage driving and meet Europe's global-warming targets, then what will it take here? Americans, who get angry enough over $3 gas, will want answers to this and other economic questions before they buy into any climate policy.

A realistic discussion about costs can't be sidestepped much longer. Once it commences, it has the potential to greatly sap the momentum for these bills.

Bursting the Climate Fear Bubble
In the last year or so, the coverage of climate science has gotten more apocalyptic in tone. This is not so much a change in the underlying science as a change in the way it is being communicated to the public. The cap-and-trade proponents have cranked up the gloom and doom for a reason -- they essentially had to. The issue in the U.S. was dead in the water without it. Previous efforts to move cap-and-trade bills had been easily defeated, and proponents needed to shake things up. For now, it is working.

But fear is two-edged sword. It can be used to whip up support for action over the near term, but it is hard to sustain for long, especially if it is not well supported by fact. Eventually it could lead to a backlash. Indeed, the global-warming doomsayers may well prove to be their own worst enemy, with their credibility taking a tumble along with the prospects for cap-and-trade legislation.

One over-utilized source, employed in spreading this kind of fear, is supposedly rock-solid "scientific consensus" on global warming, a consensus that has significant outer limits. Virtually everything the public has been told about global warming that sounds terrifying is not true and lies outside that consensus. And what is true and fully accepted by most scientists really isn't particularly terrifying.

Consider the two scariest and most attention-grabbing claims from An Inconvenient Truth -- rising sea levels and deadlier hurricanes. Gore devotes considerable attention to the horrible consequences of an 18- to 20-foot rise in sea level over an unspecified time frame, including computer graphics showing major parts of coastal cities like New York and San Francisco and even entire regions, like South Florida, under water. Yet the IPCC report (which Gore considers to be the gold standard of consensus science) projects an increase of 7 to 23 inches over the next century. The lower end of that range is about what has occurred -- without serious consequences -- over the last two centuries. Of course, the public doesn't closely follow the details of global-warming science, but the disjunction between hype and reality is so big that even casual observers can smell a rat.

In addition, Gore couldn't resist exploiting Hurricane Katrina, America's deadliest natural disaster in years. He blames global warming for the storm that claimed over 1,000 lives in August 2005, driving home the message with image after image of post-Katrina devastation. Gore asserts that Katrina portends a dangerous new era where deadlier storms are more common. But how then to explain the 2006 hurricane season, which was unusual only in how little hurricane damage occurred?

Global warming or not, we will get our share of hurricanes. But if we go yet another year without anything as bad as Katrina, the public may realize, quite rightly, that Gore simply engaged in opportunism, and that no global warming-induced pattern of deadlier hurricanes exists. If people start to feel that they have been lied to about these and other global-warming catastrophe scenarios, it could spell the end for cap-and-trade legislation.

The current Congress has pledged to make a go of enacting cap-and-trade legislation, actually pegging it as a top priority when they took over in January. But beyond holding innumerable hearings on pending bills, the House and Senate have done little since, except put off their initial deadlines for action. This may be a first sign that their momentum is slowing. And with the current trends currently pushing their way into the debate, things are not going to get any easier for them in the months and years ahead.

Ben Lieberman is senior policy analyst in the Thomas A. Roe Institute for Economic Policy Studies at the Heritage Foundation.