Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo

 

Unsupported browser: Your browser does not meet modern web standards. See how it scores »

{ action.text }

Fables About the Atmosphere and Climate

There is no evidence that global warming is real.

The climatic system is exceedingly complex and not entirely understood, but some facts are indisputable. First, scientists have known for more than a century that releasing carbon dioxide could add to the greenhouse effect caused by the gaseous composition of earth’s atmosphere. The atmosphere contains an array of natural greenhouse gases-including water vapor, carbon dioxide, and methane-that are relatively transparent to the incoming short-wavelength energy of sunlight but relatively opaque to the long-wavelength infrared energy radiated upward by the sunlight-warmed earth. The greenhouse gases and clouds together absorb most of this outgoing infrared energy and reradiate some of it back toward earth, thus functioning as a heat-trapping blanket over the planet. The naturally occurring concentrations of these gases are enough to raise earth’s average surface temperature to about 59 degrees F. Without greenhouse gases, it would be about 0 degrees, the oceans would be frozen to the bottom, and life as we know it would be impossible.

Second, scientists also know that humanity is adding to the greenhouse effect-that the atmospheric concentration of carbon dioxide in 1992 was some 30 percent above preindustrial levels, and the concentration of methane has increased by 145 percent. Both gases are natural atmospheric constituents whose concentrations have fluctuated substantially in geologic history. But analyses of air trapped in ice cores from the Antarctic and Greenland ice caps show that today’s levels are by far the highest concentrations of these greenhouse gases in at least the past 160,000 years. Moreover, nitrous oxide, another greenhouse gas, has increased about 15 percent over its preindustrial level. And chlorofluorocarbons (CFCs)-the ozone-destroying chemicals-also contribute to the greenhouse effect.

Thermometers worldwide have documented nearly a full 1-degree rise since the nineteenth century. Furthermore, a consensus has formed in the climatological community that a “discernible signal” of anthropogenic warming is beginning to emerge from the “noise” of natural climatic variation. In fact, the 1995 report of the scientific committee of the Intergovernmental Panel on Climate Change (IPCC) stated that based on the warming recorded over the past century, and especially in recent decades, “the balance of evidence suggests that there is a discernible human influence on global climate.”

Global warming exists only in computer simulations.

The IPCC’s conclusion was, indeed, based primarily on a new generation of computer simulations. But the results were also based on detailed comparisons with actual temperature records. Moreover, the total body of evidence that the planet is warming is now overwhelming. For example, surface-temperature records, even when corrected for the effects of urban “heat islands” (areas artificially heated by structures such as buildings and parking lots), show that the 10 warmest years in the past 140 years have all occurred since 1980. And the most recent satellite measurements show that shrinkage in Arctic sea ice, another expected result of global warming, accelerated significantly between 1987 and 1994.

Even if the concentration of carbon dioxide doubled, since it is responsible for only 1 percent of the greenhouse effect it wouldn’t contribute to global warming.

By itself, a doubling of CO2 (which, incidentally, accounts for some 10 to 25 percent of the natural greenhouse effect, not 1 percent) would warm earth by less than 2 degrees F. But therein lies the power of positive feedback. A 2-degree rise in temperature would cause more water to evaporate from the oceans and thus contribute additional water vapor to the greenhouse effect, resulting in a final warming most climatologists project to be a little less than 4 degrees. But if the complicating ice and cloud feedbacks are added in, models suggest that anywhere from 3 to 9 degrees of warming would result from a doubling in CO2 levels. Scientists cannot make more accurate predictions at the moment because of uncertainties surrounding the feedback processes, yet most think the upper limit represents ecological disaster. For example, 9 degrees is about the difference in global average temperature that separates today’s climate from that of the last ice age, when the present site of New York City was visited by a mile-thick glacier.

If the average mean temperature of the world were to rise a few degrees in the next century, we could simply wear lighter clothes and use more air-conditioning.

The idea that the primary reason to be concerned about global warming is that our backyards will be a little hotter during the summer barbecue season is as pervasive as it is wrong. The larger problem is that climate change could seriously disrupt a food-production system that already is showing signs of stress. Other potential problems include sea-level rise, which would result in coastal flooding and salinization of groundwater, as well as more intense storms. Finally, natural ecosystems-our life-support systems-will have great difficulty adjusting to rapid climate change. The trees in southern forests can’t just fly up to New England or put on a lighter shirt when the heat becomes too much for them.

CFCs can’t rise 18 miles into the atmosphere to deplete the ozone layer because they are made from molecules that are 4 to 8 times heavier than air.

This statement reveals an outrageous misconception about the dynamics of the atmosphere. Gases of the atmosphere are not layered like a lasagna. If they were, the lowest few feet of atmosphere would consist of krypton, ozone, nitrous oxide, carbon dioxide, and argon. Above that would be a thick layer of pure oxygen, and above that an even thicker layer of pure nitrogen followed by water vapor, methane, neon, helium, and hydrogen. In fact, the atmosphere undergoes dynamic mixing, dominated by motions of large air masses, which thoroughly mixes light and heavy gas molecules. Because of this mixing, CFCs have been detected in literally thousands of stratospheric air samples by dozens of research groups all over the world.

The chlorine in CFCs is not likely to deplete the ozone layer because volcanoes pump out 50 times more chlorine annually than an entire year’s production of CFCs.

Mount Erebus does pump out 50 times more chlorine per year in the form of hydrogen chloride (HCl) than humanity adds in CFCs. But the statement is irrelevant to depletion of the ozone layer because much of the HCl released by volcanoes is dissolved in the abundant steam that is also emitted and is thus quickly rained out. Unfortunately, unlike HCl, CFCs are not water soluble and thus cannot be washed out of the atmosphere until they have been broken down. And by then, they will already have done their damage to the ozone layer.

If there were, in fact, some reduction in the ozone layer, we could simply wear more hats and sunscreen lotion to avoid skin cancer.

The direct effects of a thinning of the ozone layer-which include not only increased rates of skin cancer (including lethal melanomas) but also disruptions of the immune system-could, of course, be partially avoided by increased use of hats and sunscreen. But rubbing lotions on earth’s plants and animals would be required as well, since the most important threat from ozone depletion is to natural and agricultural ecosystems. Increases of ultraviolet-B radiation could significantly reduce yields of major crops and has been shown to have other significant adverse effects-such as mutation and immune-system impairment-in a wide variety of plants, animals, and microorganisms.

0 comments about this story. Start the discussion »

Tagged: Energy

Reprints and Permissions | Send feedback to the editor

From the Archives

Close

Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me