MAUNA LOA OBSERVATORY, Hawaii — Two miles up, above black lava fields and a white blanket of clouds, a tower rising from this U.S. government observatory gulps in some of the clear, crisp air and gets a taste of man's future on Earth.
"As big as the atmosphere is, we're influencing it," said the physicist in charge, John Barnes.
The tale told by the tower, atop a dormant Hawaiian volcano, can be read in the upward curve of a graph:
Carbon dioxide in the atmosphere, which stood at 280 parts per million two centuries ago, has climbed to 379 ppm since industrializing man began burning vast amounts of coal, oil and other fossil fuels.
There has not been, for 450,000 years, this much CO2 enveloping the planet, ice-core samples show.
The news from Mauna Loa and other monitoring stations has increasingly disturbed scientists because carbon dioxide traps heat, as do other "greenhouse gases" generated by humans, and global temperatures have, indeed, been rising -- by almost 1 degree Fahrenheit over a recent 18-year period, a relatively rapid increase, NASA experts reported in April.
Warming will disrupt our climate, possibly drying out farmlands, stirring up fiercer storms and raising ocean levels, among other impacts, says the Intergovernmental Panel on Climate Change, a U.N.-organized network of hundreds of climatologists and other researchers.
But the climate tale is far from simple. Earth's behavior -- physics, chemistry, biology -- is an infinitely complex web of feedback loops, reactions, recycling among the atmosphere, ocean, land and all their components. Knowns are countered by unknowns, certainty by uncertainty.
It was uncertainties that American oil, utility and other industries pointed to in the 1990s in fighting international efforts to cap fossil-fuel emissions. And President Bush cited the "incomplete state of scientific knowledge" when he renounced the Kyoto Protocol, the first step toward imposing those caps, in March 2001.
Then, just three months later, a National Academy of Sciences report commissioned by the Bush White House supported the U.N. panel's finding, declaring in its opening sentence: "Greenhouse gases are accumulating in the Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise."
Last year, two more prestigious organizations -- the American Meteorological Society and the American Geophysical Union -- came to similar conclusions.
In the past, skeptics on climate change often focused on discrepancies between satellite and ground temperature readings, suggesting that recent warming might be minimal. But deeper analysis has largely dispelled those doubts. By the time scientists gathered for a symposium at New York's Columbia University in April, just weeks after Mauna Loa Observatory recorded CO2 topping 379, skeptics seemed to have faded -- or at least switched to a better-safe-than-sorry view.
"I'm a skeptic," Harvard University's Michael B. McElroy told fellow scientists. "But I take out fire insurance on my home."
The temperature rise is believed to be the most rapid in at least 10,000 years.
"It's been getting warmer and we can't explain that by natural causes," Richard Alley of Pennsylvania State University said at Columbia.
"I couldn't absolutely, positively, 100% say there's no other cause, but it's consistent with carbon dioxide warming."
Climatologists will never dispel the uncertainties 100%, but they're working on it, and the Geophysical Union said computer modeling of carbon, water and other cycles governing climate had improved greatly in the last decade.
At universities and major centers worldwide -- such as the U.S. government's National Center for Atmospheric Research in Boulder, Colo., and Britain's Hadley Centre -- specialists peer into the future via supercomputers, setting in motion vast global calculations via thousands of interlocked mathematical formulas.
Weather fronts flicker past on screens in blue and white, as temperatures and rainfall, melting ice and ocean evaporation, cloud cover and myriad other factors play out over days, months, years in "general circulation models," or GCMs.
The leapfrogging of computer speed has boosted scientists' confidence.
"The models used to consist of, say, 50,000 lines of computer code," said an early modeler, V. Ramanathan of the Scripps Institution of Oceanography in San Diego. "Now they have 500,000 lines of code."
But if computer power is meeting the challenge, brainpower -- numbers of trained specialists, hands on keyboards to input, minds to analyze -- is coming up short, scientists said in a series of interviews.
"Models have become more sophisticated, but still they're missing so many things," Ramanathan said.
"Climate change probably deserves a Manhattan Project-scale effort," said Scripps meteorologist Richard C.J. Somerville, referring to the World War II atom-bomb project. "What there is is a few dozen GCM projects, each with a handful of people."