Earth is warming and at a sharply faster rate in the last 20 years than in previous decades, according to a major study released Thursday by the National Academy of Science's National Research Council (NRC).
Environmental groups said the findings are a blunt rejection of global warming skeptics, who believe warming trends are not proven by scientific data.
The new evidence released by independent scientists for the NRC said Earth's surface temperature rose about 0.4 to 0.8 degrees Celsius (0.7 to 1.4 degrees Fahrenheit) in the last century.
In the last 20 years, the earth's surface temperature was estimated to have risen by 0.25 to 0.4 degrees Celsius (0.5 to 0.7 degrees Fahrenheit).
"In the opinion of the panel, the warming trend in global-surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming during the 20th century" as a whole, according to the report filed by an 11-member panel.
The rate of warming for the century was also 30 percent greater than prior observations made by the Intergovernmental Panel on Climate Change (IPCC), an international organization.
Still, even with the new information, disparities exist between measurements of earth surface temperatures -- which are clearly rising -- and upper-air temperatures, which for some reason are not showing the same rise.
"Data collected by satellites and balloon-borne instruments since 1979 showed little warming of the low to mid-troposphere, the atmospheric layer extending to about 5 miles (8 km) from Earth's surface," the NRC report said.
Authors of the report, however, warned against making too much of the disparities, noting the contradictions do not damage the premise that Earth is increasingly warmer.
"The differences between surface and upper-air trends in no way invalidates the conclusion that the Earth's temperature is rising," said John Wallace, panel chair and professor of atmospheric sciences at the University of Washington in Seattle.
"But the rapid increase in Earth's surface temperature over the past 20 years is not necessarily representative of how the atmosphere is responding to long-term, human-induced changes, such as increasing amounts of carbon dioxide and other greenhouse gases," he said.
Proving for certain that the globe is warming is a key factor behind efforts to finalize the Kyoto Protocol, the agreement among industrialized nations to cut sharply consumption of fossil fuels blamed for quickening the warming trend.
Wallace said nations should develop an improved climate monitoring system to resolve the uncertainties in the data and provide policymakers with the best information available.
Environmental group Ozone Action said the report was "the nail in the coffin of doubt" about the reality of a warming trend.
It said environmental signs of warming are clear, noting this week Boston broke its record for consecutive days without snowfall, and a recent report that sea ice in Arctic water is shrinking by 14,000 square miles (36,400 square km) per year.
But those who doubt the warming trend said the only thing rising over the past decade is the political spin on the issue, especially by the Clinton administration.
"The report itself does not call for energy-restricting international treaties, like the Kyoto Protocol. It calls for increased monitoring of everything from temperatures, to ozone levels, to water vapor, to aerosols in order to determine what is really going on with the climate," said Myron Ebell, global warming expert for the Competitive Enterprise Institute.
