Superfreakonomics_ global cooling, patri - Steven D. Levitt [82]
“So most of the warming seen over the past few decades,” Myhrvold says, “might actually be due to good environmental stewardship!”
Not so many years ago, schoolchildren were taught that carbon dioxide is the naturally occurring lifeblood of plants, just as oxygen is ours. Today, children are more likely to think of carbon dioxide as a poison. That’s because the amount of carbon dioxide in the atmosphere has increased substantially over the past one hundred years, from about 280 parts per million to 380.
But what people don’t know, the IV scientists say, is that the carbon dioxide level some 80 million years ago—back when our mammalian ancestors were evolving—was at least 1,000 parts per million. In fact, that is the concentration of carbon dioxide you regularly breathe if you work in a new energy-efficient office building, for that is the level established by the engineering group that sets standards for heating and ventilation systems.
So not only is carbon dioxide plainly not poisonous, but changes in carbon-dioxide levels don’t necessarily mirror human activity. Nor does atmospheric carbon dioxide necessarily warm the earth: ice-cap evidence shows that over the past several hundred thousand years, carbon dioxide levels have risen after a rise in temperature, not the other way around.
Beside Myhrvold sits Ken Caldeira, a soft-spoken man with a boyish face and a halo of curly hair. He runs an ecology lab at Stanford for the Carnegie Institution. Caldeira is among the most respected climate scientists in the world, his research cited approvingly by the most fervent environmentalists. He and a co-author coined the phrase “ocean acidification,” the process by which the seas absorb so much carbon dioxide that corals and other shallow-water organisms are threatened. He also contributes research to the Intergovernmental Panel on Climate Change, which shared the 2007 Nobel Peace Prize with Al Gore for sounding the alarm on global warming. (Yes, Caldeira got a Nobel certificate.)
If you met Caldeira at a party, you would likely place him in the fervent-environmentalist camp himself. He was a philosophy major in college, for goodness’ sake, and his very name—a variant of caldera, the craterlike rim of a volcano—aligns him with the natural world. In his youth (he is fifty-three now), he was a hard-charging environmental activist and all-around peacenik.
Caldeira is thoroughly convinced that human activity is responsible for some global warming and is more pessimistic than Myhrvold about how future climate will affect humankind. He believes “we are being incredibly foolish emitting carbon dioxide” as we currently do.
Yet his research tells him that carbon dioxide is not the right villain in this fight. For starters, as greenhouse gases go, it’s not particularly efficient. “A doubling of carbon dioxide traps less than 2 percent of the outgoing radiation emitted by the earth,” he says. Furthermore, atmospheric carbon dioxide is governed by the law of diminishing returns: each gigaton added to the air has less radiative impact than the previous one.
Caldeira mentions a study he undertook that considered the impact of higher carbon-dioxide levels on plant life. While plants get their water from the soil, they get their food—carbon dioxide, that is—from the air.
“Plants pay exceedingly dearly for carbon dioxide,” Lowell Wood jumps in. “A plant has to raise about a hundred times as much water from the soil as it gets carbon dioxide from the air, on a molecule-lost-per-molecule-gained basis. Most plants, especially during the active part of the growing season, are water-stressed. They bleed very seriously to get their food.”
So an increase in carbon dioxide means that plants require less water to grow. And what happens