Bangkok, Thailand, represents one future for global transportation. Short trips last hours, whether by bus or car, and by evening traffic can average half a mile an hour in some spots, far slower than walking speed. Bangkok's nine million or so denizens support two million personal vehicles. "Unfortunately, the personal vehicle has become sort of synonymous with being a rich, civilized person," notes Steven Plotkin, a transportation energy analyst at Argonne National Laboratory in Illinois. "It's one of the first things you buy when you get some money together."

Worldwide, the desire for automobiles and the traffic it inspires burns fuel at an alarming pace, contributing to an ever increasing amount of greenhouse gases, particularly carbon dioxide. As the new report from the Intergovernmental Panel on Climate Change (IPCC) released today in Bangkok reveals, cutting back on those emissions is a critical task.

Worldwide emissions of all greenhouse gases have nearly doubled since 1970 thanks to a rise in the worldwide use of energy, whether fuel in cars or electricity from a coal-fired power plant. In that time emissions of carbon dioxide (CO2) alone rose by "about 80 percent," according to the report, with 28 percent of that increase occurring since 1990 alone. Nothing in sight will check this rise: cars are only getting more popular and more of the world is consuming coal-fired electricity. China alone added 90 gigawatts of coal-fired power plants in 2006, roughly equivalent to the total power production of Germany, according to Richard Bradley, head of the energy efficiency and environment division at the International Energy Agency (IEA) in Paris.

If CO2 levels in the atmosphere—currently 379 parts per million (ppm)—reach roughly 550 ppm, scientists estimate temperatures would rise by three degrees Celsius (5.4 degrees Fahrenheit) on average. Such a rise would have a host of impacts, ranging from shrinking glaciers (and imperiled supplies of fresh water) to extreme weather events and natural disasters such as forest fires and pest outbreaks, according to the IPCC.

Fortunately, a range of options exist to attempt to mitigate the amount of CO2 and other greenhouse gases emitted into the atmosphere. First and foremost is simply using energy wisely—so-called energy efficiency. "The most benefit with the least cost would come from energy efficiency," argues Harlan Watson, the senior climate negotiator for the U.S. "If we are going to address climate change in the long run we have to reduce and indeed reverse the growth in global emissions. The best way to do that is to employ a portfolio across many sectors."

For example, the report calls for more efficient buildings. "For new buildings, this runs the gamut from proper insulation; good windows; energy-efficient heating, cooling and ventilation; efficient appliances and plug loads that have much-reduced standby losses," says Mark Levine, a senior staff scientist at Lawrence Berkeley National Laboratory in California. "It will be possible as time goes on to construct commercial buildings that are much more energy efficient than at present." And it doesn't have to cost more. The report notes that "by 2030, about 30 percent of the projected [greenhouse gas] emissions in the building sector can be avoided with net economic benefit."

From increasing the use of low-carbon sources of energy such as nuclear and solar power to reducing the nearly 13 megahectares (about 50,200 square miles, or roughly the size of New York State) of forest cleared every year (which contributes roughly 5.8 gigatonnes of CO2 to the atmosphere annually), the report lays out ways the world can reduce emissions. Even transportation can be improved. "You can double the efficiency of the U.S. fleet [of vehicles] with technology that is in existence today," Argonne's Plotkin says. "It just takes the will."

Of course, transportation shows how difficult it will be to achieve the long-term goal of nearly eliminating greenhouse gas emissions from all sectors. "Decarbonizing will require a dramatic change in the energy supply infrastructure," notes David L. Greene, a transportation analyst at Oak Ridge National Laboratory in Tennessee. Options include hydrogen fuel cells, electric hybrids fueled with biomass or electric cars that plug into the grid. "There is not enough biofuel," Greene adds. "So you will need hydrogen or electricity to decarbonize surface transport, plus strong policies to ensure that the carbon emissions from producing these energy carriers are sequestered."

Such carbon capture and storage will be critical to any efforts to combat climate change, particularly if coal continues to play a large power generation role. Unfortunately, sequestration has yet to be demonstrated on a large scale. Significant government funding will be required to prove this technology, admits James Connaughton, chairman of the White House Council on Environmental Quality. "This report underscores the need for collective action, underscores the need for action across all sectors of the economy, and underscores the need for some breakout technologies in fossil fuel power generation as well as in the area of fuels," he says. "The goal is reducing emissions and growing economies."

The report also provides estimates of what such changes might cost. These estimates range from an actual improvement of overall economic health to a loss of as much as 3 percent of global gross domestic product by 2030, depending on what level of greenhouse gases in the atmosphere is targeted. But "costs may be substantially lower under the assumption that revenues from carbon taxes or auctioned permits under an emission trading system are used to promote low-carbon technologies," the report notes; associated health benefits, such as decreased particulate pollution from cars, could make stringent action economically beneficial.

"The IPCC report demonstrates that costs can be manageable if action begins soon and is clearly articulated," IEA's Bradley adds. "Because of the long-lived nature of the energy supply capital those investment decisions are needed now."

That will require leadership on both domestic and international levels from the U.S., the world's largest developed emitter, which has yet to commit to international reduction targets or even a preferred level of atmospheric concentrations of greenhouse gases. "The U.S. taking a step is the next major thing to happen," says Billy Pizer, a senior fellow at the Washington, D.C.-based think tank Resources for the Future. "I don't know if it's going to happen in this administration but I think it's possible. It is not impossible to imagine this president coming up with a proposal."

Voluntary measures, like those the U.S. government currently employs, will not be enough. "Voluntary measures will not work, though they have some very modest impact," says Charles Kolstad, an economist at the University of California, Santa Barbara. "Countries need to take actions that provide incentives to individuals and businesses to reduce carbon—a price needs to be put on carbon."

According to the report and its authors, whatever action governments undertake will need to be faster than the sluggish flow of Bangkok traffic. "Mitigation efforts over the next two to three decades will have a large impact on opportunities to achieve lower stabilization levels," the report says. In transportation, it offers mandatory fuel economy standards and better infrastructure planning as ways to both avoid the nightmare of catastrophic climate change and urban gridlock.

"The short term is efficiency," Argonne's Plotkin says. And in the longer term? "Urban form has a big effect on how people travel and also what kinds of public transportation you can have. This is a long term thing but you have to start somewhere soon."