The Why Files The Why Files --

The fact of global warming

POSTED 24 FEB 2005
Kyoto agreement: Law at last
world map with Kyoto highlightedEight years after it was negotiated, the Kyoto protocol for controlling greenhouse gases and global warming has gone "into force." By 2012, the 141 signatory nations have agreed to reduce their emissions of carbon dioxide, methane and other greenhouse gases to about 95 percent of 1990 levels.

At the same time, we see plenty of evidence that the planet is heating up.

The global climate warmed 0.6 °C over the past century, mainly in the last 50 years. The United States, the world's biggest smokestack, shuns Kyoto, claiming it lets fast-growing sources of greenhouse gases, like China and India, off the hook.

After carbon dioxide enters the atmosphere, it can reflect heat back to Earth for a century. So today's pollution can bother unborn generations.

In 2003, 21,000 to 35,000 Europeans died during the warmest summer in 500 years.

The oceans, covering 71 percent of Earth, are warming. Glaciers are melting almost everywhere, and sea ice is disappearing in the Arctic.

Animals are moving toward the poles and changing their behavior to survive a warming world

Global warming is already under way, according to almost everybody who looks seriously at the issueGlobal warming is no longer tomorrow's problem. Whether you look at oceans or ice, at the atmosphere or at life on Earth, you can see warming beginning. The picture is largely what the early computer climate models predicted: more warming toward the poles, gradual warming that starts to accelerate, side-effects of warming appearing in unexpected places.

Beyond a reasonable doubt
It's not just warming. People who look seriously at the situation blame the heat-up mainly on our habit of burning fossil fuels. As we'll see, even scientists working for the major greenhouse-skeptic nation are convinced that we are warming Earth by spewing greenhouse gases into the sky. The case is settled, beyond a reasonable doubt.

Still, Kyoto is a bittersweet victory, because some important polluters remain aloof from the global consensus, and the limited roll-back of emissions is too feeble to stabilize the warm-up. Still, the protocol may be worth celebrating, says Penn State geoscientist Richard Alley, who studies the effects of warming. "It doesn't do much, but then it does a lot. It's somehow a statement that the world is going to try to do something about this."

Smokestacks loom as cars travel down a highway flanked by powerlinesIn Kansas City, you can see primary air pollution -- smokestack and auto emissions -- and secondary pollution -- smog, produced when solar radiation strikes primary pollutants. Photo: EPA

Even if Kyoto cannot, by itself, prevent warming, Alley sees hope in history. "If we went back and looked at the start of the civil rights movement or environmental regulation, you don't solve everything with the first law. It's saying that a lot of the world wants to get together, but will Kyoto end the CO2 [carbon dioxide] problem? Of course not."

While Kyoto does not directly limit India's carbon emissions, the treaty's "carbon reduction credits" may induce rich countries to support green energy projects in developing countries like India.

 Graph shows dramatic increase of temperature in past 50 years.
A controversial graph shows radical warming in the past 50 years or so. Graph: IPCC

Computer climate models. Do they work?
The concern about global warming is based on climate predictions, and now that Kyoto is finally in effect, The Why Files decided to take a fresh look at those predictions. We got help from the American Association for the Advancement of Science, which scheduled more than a dozen global warming talks at its 2005 annual meeting in Washington, D.C. The sheer number of talks shows that the world's largest general scientific society takes warming seriously.

Global warming is complicated, but the basic mechanism is not. Common "greenhouse" gases like carbon dioxide and methane trap heat that would otherwise leave Earth. Normally, this "greenhouse effect" keeps Earth comfortably warm. But as we continue burning fossil fuels, they accumulate in the atmosphere, and too much of a good thing is not a good thing.

Graph shows dramatic increase of carbon dioxide concentration over 1000 years.
As carbon dioxide rises, it reflects more heat back to earth. "Radiative forcing" shows how carbon dioxide affects the planet's heat balance.
Graph: IPCC

The ultimate result of greenhouse warming is hard to predict, but the direction of the change is not: You trap more heat, you get hotter.

Computer climate models are elaborate versions of the software used to forecast weather. As the models get more accurate, they are starting to look at regional change, not just global change. Donald Wuebbles, a professor of atmospheric science at the University of Illinois, recently modeled the climate of the Great Lakes. By 2100, he estimates, summer temperatures will rise 9 ° to 18 ° F.

Illinois, meet East Texas
By 2030, Wuebbles adds, the climate of Illinois will resemble what you now find in Arkansas. By 2100, the Land of Lincoln will look like hot, humid East Texas. And these calculations, he says, did not even include the extreme projection of the Intergovernmental Panel on Climate Change.

The IPCC, created by the United Nations to be the global authority on global warming, collaborates with thousands of climate scientists. The third IPCC report, issued in 2001, said that in about 60 years, when atmospheric CO2 reaches twice the pre-industrial level, average air temperatures near the ground will rise 1.8° C to 5.8 ° C (3.2 ° F to 10.4° F). The exact rise will depend on future patterns of population, economics and technology.

Ever since scientists started predicting global warming 20 or more years ago, skeptics have mocked their computer models as untrustworthy and untested. But now, several groups of scientists have compared the models to reality, and found that the models work.

At the same time, there is more and more evidence that our world is heating up.

Graph shows prediction of rapid warming of planet over decades.
The United Nations group that tracks global warming forecasts different levels of warming, based on different assumptions about population, energy usage and economic growth. All show a sudden spike in temperatures over the next decades. Graph: IPCC

Global warming due to man-made greenhouse gases is no longer just a prediction; climate is not going through a natural variation, Wuebbles says. "You cannot explain the recent change in climate without global warming. Climate change is already under way."

Global warming models. Are they all wet?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

©2023, University of Wisconsin, Board of Regents.