Global warming is ``very likely'' caused by humans, and temperatures and sea-levels will increase by the end of the century, the UN said in its most comprehensive report yet on climate change.

Global temperatures are likely to rise by 1.1 to 6.4 degrees Celsius by the end of this century relative to the last, with a probable 2 to 4.5 degree range if carbon dioxide doubles from pre-industrial levels, the United Nations Intergovernmental Panel on Climate Change said in the report. Sea-level gain over the same period may range from 18 to 59 centimeters (7 to 23 inches), it said.

A key change in the report's language from that used in the panel's 2001 document showed there is more certainty that human activity is causing the warming. The report, released to reporters in Paris, puts the probability of the link at more than 90 percent, compared with the 66 to 90 percent likelihood signaled in 2001.

``This report puts a full stop behind the questioning of the science underlying the issue of whether humans are causing global warming,'' Achim Steiner, director of the UN Environment Program, said in an interview in Paris. ``This is critical because it allows us to now shift the attention to what kind of policy responses and international initiatives we need to achieve emissions reductions.''

`Smoking Gun'

The global atmospheric concentration of carbon dioxide (CO2) stood at 379 parts per million in 2005, up from about 280 ppm in 1750, before the industrial revolution, the report said. Concentrations of CO2, and methane, another greenhouse gas, exceed ``by far'' the highest in an Antarctic ice-core record stretching back 650,000 years. Those increases are primarily attributable to fossil fuel use and land-use change, Susan Solomon, who chaired talks this week, said at a Paris news conference.

``This is a statement by the largest scientific panel ever put together on a major scientific issue that we now have the smoking gun on global warming,'' said Philip Clapp, president of the U.S. National Environmental Trust in a Jan. 31 phone interview after seeing portions of the draft.

The panel released part one of a four-volume survey, which was reviewed by more than 2,500 scientists from 130 countries. Discussions on the final wording continued past midnight as scientists and political negotiators sought consensus.

Rise in Sea-Levels

On the rise in sea-levels, language was added to the statement to reflect concerns that the new forecast doesn't bear in mind recent discoveries and so underestimates the potential, said Sharon Hays, associate director of the U.S. Office of Science and Technology Policy, in a telephone interview today. She didn't have the exact forecasts.

``The concern was that the current models don't take into account the melting and breakup of the ice that we're currently seeing,'' Hays said. ``The report now addresses this issue in a very appropriate way. It still has the same measurements for the models, but it states very clearly that there is expected to be increased sea level rise because of this breakup of the ice.''

The IPCC's report issued today is entitled ``Climate Change 2007: the Physical Science Basis.''

``The science of climate change, of global warming, is now unambiguous: the Earth is getting hotter, the weather is becoming more variable and this is due to our own industrial revolution,'' U.K. Environment Secretary David Miliband said in a Jan. 31 interview. ``All the predictions are that the problem is becoming more urgent, that the scientists are becoming more certain and that the dangers are becoming more real.''

Greenland Ice Sheet

Scientists say that carbon dioxide (CO2) and other gases produced by burning fossil fuels cause the Earth to heat up when they linger in the atmosphere, trapping energy from the sun that would otherwise reflect back into space.

Scientists at the University of Texas at Austin on Aug. 10 said in the journal Science that melting of Greenland's ice sheet ``increased dramatically'' in the past few years, with one portion losing ice five times faster in the past two years than the previous year and a half.

The breakup in 2002 of the Larsen B ice shelf opened the way for the west Antarctic ice sheet's glaciers to flow faster, accelerating melting. ``A number of scientists are now saying the west Antarctic ice sheet is the awakened giant of climate change, and that is the truly catastrophic risk,'' Clapp said.

`More Urgency'

Sea-level forecasts will be under more scrutiny following a report yesterday in Science saying levels since 1993 have risen by 3.3 millimeters (0.13 inch) a year compared with the IPCC's 2 millimeter best-estimate from 2001.

Overall, the IPCC is signaling ``more urgency'' on sea-level changes, melting glaciers ice caps and sea ice, one of the report's editors, Roger Barry, said in a Jan. 26 interview. Barry is director of the U.S. National Snow and Ice Data Center in Boulder, Colorado.

Many industrialized nations have already begun taking action by setting caps on emissions. Under the UN's Kyoto Protocol treaty, 35 countries and the European Union agreed to cut emissions of greenhouse gases by a combined 5 percent from 1990 levels by the 2008-2012 period.

The U.S. and Australia didn't ratify the treaty, and developing nations such as India and China aren't subject to emissions reductions.