Human-caused global warming is here - visible in the air, water and melting ice - and is destined to get much worse in the future, an authoritative global scientific report will warn next week.

"The smoking gun is definitely lying on the table as we speak," said top U.S. climate scientist Jerry Mahlman, who reviewed all 1,600 pages of the first segment of a giant four-part report. "The evidence . . . is compelling."

The first phase of the Intergovernmental Panel on Climate Change is being released in Paris next week. This segment, written by more than 600 scientists and reviewed by another 600 experts and edited by bureaucrats from 154 countries, includes "a significantly expanded discussion of observation on the climate," said co-chair Susan Solomon, a senior scientist for the U.S. National Oceanic and Atmospheric Administration. She and other scientists held a telephone briefing on the report Monday.

That report will feature an "explosion of new data" on observations of current global warming, Solomon said.

Solomon and others wouldn't go into specifics about what the report says. They said that the 12-page summary for policymakers will be edited in secret word-by-word by governments officials for several days next week and released to the public Feb. 2. The rest of that first report from scientists will come out months later.

The full report will be issued in four phases over the year, as was the case with the last IPCC report, issued in 2001.

Later this week in Paris, climate scientists will issue a dire forecast for the planet that warns of slowly rising sea levels and higher temperatures. But that may be the sugarcoated version.

Early and changeable drafts of their upcoming authoritative report on climate change foresee smaller sea level rises than were projected in 2001 in the last report. Many top U.S. scientists reject these rosier numbers. Those calculations don't include the recent, and dramatic, melt-off of big ice sheets in two crucial locations:

They "don't take into account the gorillas - Greenland and Antarctica," said Ohio State University earth sciences professor Lonnie Thompson, a polar ice specialist. "I think there are unpleasant surprises as we move into the 21st century."

Even so, there are questions about how permanent the melting in Greenland and especially Antarctica are, said panel lead author Kevin Trenberth, chief of climate analysis at the National Center for Atmospheric Research in Colorado.

While he said the melting ice sheets "raise a warning flag," Trenberth said he wonders if "some of this might just be temporary."

University of Alabama at Huntsville professor John Christy said Greenland didn't melt much within the past thousand years when it was warmer than now. Christy, a reviewer of the panel work, is a prominent so-called skeptic. He acknowledges that global warming is real and man-made, but he believes it is not as worrisome as advertised.

Those scientists who say sea level will rise even more are battling a consensus-building structure that routinely issues scientifically cautious global warming reports, scientists say. The IPCC reports have to be unanimous, approved by 154 governments - including the United States and oil-rich countries such as Saudi Arabia - and already published peer-reviewed research done before mid-2006.

Rahmstorf, a physics and oceanography professor at Potsdam University in Germany, says, "In a way, it is one of the strengths of the IPCC to be very conservative and cautious and not overstate any climate change risk."