A Scientist, His Work and a Climate Reckoning

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In 2007, a body appointed by the United Nations declared that the scientific evidence that the earth was warming had become unequivocal, and it added that humans were almost certainly the main cause. Mr. Gore and the panel jointly won the Nobel Peace Prize.

But as action began to seem more likely, the political debate intensified, with fossil-fuel industries mobilizing to fight emission-curbing measures. Climate-change contrarians increased their attack on the science, taking advantage of the Internet to distribute their views outside the usual scientific channels.

In an interview in La Jolla, Dr. Keeling’s widow, Louise, said that if her husband had lived to see the hardening of the political battle lines over climate change, he would have been dismayed.

“He was a registered Republican,” she said. “He just didn’t think of it as a political issue at all.”

The Numbers

Not long ago, standing on a black volcanic plain two miles above the Pacific Ocean, the director of the Mauna Loa Observatory, John E. Barnes, pointed toward a high metal tower.

Samples are taken by hoses that snake to the top of the tower to ensure that only clean air is analyzed, he explained. He described other measures intended to guarantee an accurate record. Then Dr. Barnes, who works for the National Oceanic and Atmospheric Administration, displayed the hourly calculation from one of the analyzers.

It showed the amount of carbon dioxide that morning as 388 parts per million.

After Dr. Keeling had established the importance of carbon dioxide measurements, the government began making its own, in the early 1970s. Today, a NOAA monitoring program and the Scripps Institution of Oceanography program operate in parallel at Mauna Loa and other sites, with each record of measurements serving as a quality check on the other.

The Scripps program is now run by Ralph Keeling, who grew up to become a renowned atmospheric scientist in his own right and then joined the Scripps faculty. He took control of the measurement program after his father’s sudden death from a heart attack.

In an interview on the Scripps campus in La Jolla, Ralph Keeling calculated that the carbon dioxide level at Mauna Loa was likely to surpass 400 by May 2014, a sort of odometer moment in mankind’s alteration of the atmosphere.

“We’re going to race through 400 like we didn’t see it go by,” Dr. Keeling said.

What do these numbers mean?

The basic physics of the atmosphere, worked out more than a century ago, show that carbon dioxide plays a powerful role in maintaining the earth’s climate. Even though the amount in the air is tiny, the gas is so potent at trapping the sun’s heat that it effectively works as a one-way blanket, letting visible light in but stopping much of the resulting heat from escaping back to space.

Without any of the gas, the earth would most likely be a frozen wasteland — according to a recent study, its average temperature would be colder by roughly 60 degrees Fahrenheit. But scientists say humanity is now polluting the atmosphere with too much of a good thing.

In recent years, researchers have been able to put the Keeling measurements into a broader context. Bubbles of ancient air trapped by glaciers and ice sheets have been tested, and they show that over the past 800,000 years, the amount of carbon dioxide in the air oscillated between roughly 200 and 300 parts per million. Just before the Industrial Revolution, the level was about 280 parts per million and had been there for several thousand years.

That amount of the gas, in other words, produced the equable climate in which human civilization flourished.

Other studies, covering many millions of years, show a close association between carbon dioxide and the temperature of the earth. The gas seemingly played a major role in amplifying the effects of the ice ages, which were caused by wobbles in the earth’s orbit.

The geologic record suggests that as the earth began cooling, the amount of carbon dioxide fell, probably because much of it got locked up in the ocean, and that fall amplified the initial cooling. Conversely, when the orbital wobble caused the earth to begin warming, a great deal of carbon dioxide escaped from the ocean, amplifying the warming.

Richard B. Alley, a climate scientist at Pennsylvania State University, refers to carbon dioxide as the master control knob of the earth’s climate. He said that because the wobbles in the earth’s orbit were not, by themselves, big enough to cause the large changes of the ice ages, the situation made sense only when the amplification from carbon dioxide was factored in.

“What the ice ages tell us is that our physical understanding of CO2 explains what happened and nothing else does,” Dr. Alley said. “The ice ages are a very strong test of whether we’ve got it right.”

When people began burning substantial amounts of coal and oil in the 19th century, the carbon dioxide level began to rise. It is now about 40 percent higher than before the Industrial Revolution, and humans have put half the extra gas into the air since just the late 1970s. Emissions are rising so rapidly that some experts fear that the amount of the gas could double or triple before emissions are brought under control.

The earth’s history offers no exact parallel to the human combustion of fossil fuels, so scientists have struggled to calculate the effect.

by NYtimes