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That’s unequivocal; now what?

The concept that humans might precipitate climate change has been publicly discussed for five decades. Now, experts around the world — including many at the University of Colorado — enlarge our understanding of the science of climate change and help society make wise choices for the future.

In 1958, the National Academy of Sciences identified carbon dioxide and water vapor as “greenhouse” gases, which “allow the sun’s short-wave heat rays to penetrate to the Earth’s surface, but keep much of the long-wave heat radiated by the Earth from escaping to outer space. This heats our atmosphere.

“Our industrial civilization has been pouring carbon dioxide into the atmosphere at a great rate,” the National Academy observed, adding that much of the CO2 “will probably be absorbed” by the oceans. “Conceivably, however, it could cause significant melting of the great icecaps and raise sea levels in time.”

Those comments from a half-century ago, highlighted in August at a University of Colorado conference titled “Meeting the Global Energy and Climate Challenge,” originally appeared in a National Academy booklet titled “Planet Earth: The Mystery With 10,000 Clues.”

Similar warnings came in 1965, when President Lyndon B. Johnson’s Science Advisory Committee warned that “by the year 2000 there will be about 25 percent more CO2 in our atmosphere than at present, (and) this will modify the heat balance of the atmosphere to such an extent that marked changes in climate … could occur.”

The 1965 White House report said the climatic changes from rising levels of atmospheric CO2 “could be deleterious from the point of view of human beings,” potentially causing unusually rapid melting of ice caps and rising of sea level.

In the last 43 years, legions of scientists publishing thousands of peer-reviewed journal articles have brought the picture into sharper focus. The scientific consensus is that warming of the Earth in the last half-century is “unequivocal,” and most of the observed increase in global average temperatures is very likely due to increased concentrations of greenhouse gases.

Those statements come from the Intergovernmental Panel on Climate Change, which produced the most thoroughly vetted scientific assessments in history and which last year shared the Nobel Peace Prize with former Vice President Al Gore.

As speakers at the university’s conference on climate and energy emphasized, humanity faces enormously complex challenges. Leading thinkers and researchers at CU — some of whom made significant contributions to the IPCC — are helping society understand what we know, how well we know it, what the future might hold, and how society should strive to reduce the extent of climate change and its impacts.

What follows is a summary of CU researchers’ work on observed climate change, ice melt and ocean rise, long-term climate projections, and policy implications of it all.

“Climate change” sounds monolithic, but it comprises multitudes of specific transformations. University of Colorado scientists are among the many researchers recording the details.

Scientists don’t know how much the seas will climb by the century’s end. But given current trends, experts agree, the steadily rising tides will take a toll.

Climate projections help people make social and economic decisions. And even when impacts are uncertain, experts recognize a need to prepare. From Colorado resorts to African slums, leaders eye the future climate.

Polluting less is a good idea. But in the context of climate, experts say, emitting less carbon is not enough.