For decades lawmakers and others have debated the complex and politicized issue of changes to the Earth's climate, largely failing to find the consensus needed to implement and consistent national policy.

Scientists have reported different rates of warming at the Earth's surface and in the midsection of the atmosphere, called the troposphere. These disparities have been cited by the Bush administration and some scientists to question the growing consensus among climatologists that heat-trapping gases could dangerously warm the Earth.

President Bush and his administration have consistently said climate change data are incomplete and have moved to dramatically increase funding for scientists, saying more research was needed to better understand the issue.

At his first press conference on climate change in September 2001, the president acknowledged global warming is occurring. However, the influence of human activity on the Earth's temperature is still unknown, the administration has said.

"Climate change is an issue that must be addressed by the world," President Bush said in 2001. "First we know that the surface temperature of the earth is warming. It has risen by 0.6 degrees Celsius over the past 100 years. There was a warming trend from the 1890s to the 1940s.

Cooling from the 1940s to the 1970s, and then sharply rising temperatures from the 1970s to today."

The United States has spent $18 billion on climate research since 1990 -- three times as much as any other country.

The current administration has earmarked about $2 billion a year for climate monitoring and research, including the creation of the Climate Change Science Program to address what it calls unresolved questions. The program released a much anticipated report in May 2006 aimed at resolving conflicting records of atmospheric temperature trends.

The studies confirmed warming in the troposphere and at the surface of the Earth.

"The patterns of climate change over the past 50 years cannot be explained by natural phenomenon alone and show clear evidence of human influences on the climate system (due to changes in greenhouse gases, aerosols, and stratospheric ozone)," the report found.

"There is no longer a discrepancy in the rate of global average temperature increase for the surface compared with higher levels in the atmosphere," the report said. It also concluded that man-made emissions, mainly caused by burning coal and oil, were driving the change in the global climate.

The administration's policy remains focused on studying the remaining questions -- 20 other assessments from the Climate Change Science Program are under way -- and using voluntary means to slow the growth in emissions of heat-trapping gases such as carbon dioxide.

In Congress, the views widely vary among those who trumpet the environmental damages caused by global warming and those who the economic disruption that could be caused by expensive anti-pollution mandates.

Senate Environment and Public Works Committee Chairman James Inhofe, R-Okla., has said "much of the debate over global warming is predicated on fear, rather than science." And the threat of catastrophic global warming is the "greatest hoax ever perpetrated on the American people."

Skeptics have seized on satellite measurements that suggest the atmosphere is not heating up to bolster their argument that there was no link between climate change and man-made emissions.

Other lawmakers have introduced legislation aimed at dealing with the impacts of global warming while preserving business interests.

For example, Sens. John McCain, R-Ariz., and Joe Lieberman, D-Conn., reintroduced the Climate Stewardship Act to cap and trade greenhouse gases.

The bill, which has a similar House version, would create mandatory restrictions on emissions of carbon dioxide and created a mechanism for stricter limits in the style of the Kyoto Protocol climate treaty.

The legislation has drawn some opposition in both the environmental and business communities for different reasons. In essence, they believe that a more affordable and reliable restriction could be enacted.

Another bipartisan offering, the Keep America Competitive Global Warming Policy Act from Reps. Tom Udall, D-N.M., And Tom Petri, R-Wis., would cap prices for greenhouse gas credits at about $7 per ton but would not set an emissions cap, instead giving the U.S. Environmental Protection Agency three years after the date of enactment to set one.

Some environmentalists, including David Doniger, policy director at the Natural Resources Defense Council's Climate Center, criticize the legislative proposals for not containing enough conservation elements.

"There's a race to the bottom going on," he said. "Because of the 'just say no' attitude in Congress, you have lawmakers trying to get to 'yes' by negotiating compromises so great they no longer offer meaningful climate solutions."

-- By Kathryn Cohen, Online NewsHour