Undergraduate Environmental Science Program

Rensselaer




CARBON DIOXIDE AND THE GLOBAL CLIMATE



From:

Paradise for Sale

by Carl N. McDaniel and John M. Gowdy, University of California Press, 2000.


"The earth has its climate because greenhouse gases like carbon dioxide and water in our atmosphere allow light energy to pass through but absorb some of the longer wave lengths of heat energy that radiate from earth. As a consequence, the earth's climate is controlled by the amount of sunlight, and subsequently heat energy, that reaches the atmosphere, the land, and the oceans. Latitude dictates the amount of energy received; equatorial regions get more heat than do polar regions. The dynamic nature of global climate mainly results from physical processes, like ocean currents and winds, that equalize this difference. Certainly these processes are major causes of local weather. The solar energy input to the earth also depends on the variable output from the sun and the earth's changing distance to it. Local energy input is related to surface cover (water, snow, ice, brown soil, green plants) and local atmospheric composition (clouds, water vapor, particulate matter, sulfates). The equation is, in a word, complex, as is evident in our poor record for weather prediction. Even though we spend billions of dollars and employ thousands of people to collect and analyze atmospheric data to predict weather for the next several days, we know from personal experience that near-term weather forecasts are only modestly accurate. It is not surprising that we can't predict in any detail next year's, much less next century's, weather.

Even so, human activities have influenced local climates for millennia. Within the past hundred years we now know our activities influence global climate. Climate change has figured prominently in all of human history. What is different now, though, is that human activities on a global scale -- deforestation and burning of fossil fuels, to name a couple -- are big contributors to the rise in atmospheric concentrations of carbon dioxide of about 30 percent over the last hundred years, from 280 parts per million to over 360 parts per million. Carbon dioxide absorbs radiant energy at some wave lengths not absorbed by other greenhouse gases; thus, when the carbon dioxide concentration in the atmosphere increases to a new level, more heat energy is retained and the planet becomes warmer until a new equilibrium is reached. If no carbon dioxide were in the atmosphere, the planet's temperature would drop below the freezing point of water, and life as we know it would not have evolved. By contrast, if we had as much carbon dioxide as Venus's sizzling-hot atmosphere, Earth too would be several hundred degrees Celsius. Again, the conditions would not permit life.

Atmospheric scientists around the world have reached consensus that this human-caused rise in atmospheric carbon dioxide and other greenhouse gases will warm the planet considerably during the next several hundred years, depending on how high the levels of carbon dioxide and other greenhouse gases go. But nobody knows how much or how long it will take. The greater energy differential between equatorial and polar regions may increase the number and severity of storms. Local climate changes, which determine the regions that will be wetter or drier, are difficult if not impossible to predict.

Global warming would not be good for the people of Nauru. If the South Pole warms enough to release say 10 percent of the water now stored in snow and ice, the coastal strip of land on Nauru would be submerged and the island would be uninhabitable. Worldwide, the more than a billion people who live close to sea level might lose their homes. Where will they live and how will they obtain the necessities of life if their homes and associated biological support systems are under water?

Climate change will necessitate the migration of organisms and whole ecosystems to areas where prospects for survival are better -- a move that will lead to the extinction of others. Many will be unable to make the move because of the formidable barriers imposed by humans -- highways, agricultural land, cities and industrial areas. The more quickly the climate changes, the more difficult migration will be; the rate of extinction will accelerate accordingly. Humans will experience severe turmoil caused by the immense challenges associated with adjusting to warmer and more unstable climates. The loss of biological diversity will make the adjustments even more problematic.

This episode of civilization-disrupting global warming caused by greenhouse gases may, ironically, trigger a devastating global cooling, perhaps another ice age. Chicago at 42 degrees N latitude is blustery cold in February, while London and Paris at 49 degrees N latitude only have temperatures below freezing occasionly. The climates of North America and Europe are vastly different because of the Gulf Stream. These currents are part of a complex and incompletely understood global pattern of ocean circulation that mixes ocean waters and helps to redistribute equatorial solar energy. Paleoclimatologists have established that the ocean currents are not constant; they flip from time to time to different patterns. We now have evidence that when the Gulf Stream no longer reaches into the North Sea, Europe's climate becomes like North America's and the rest of the world gets colder.

The Gulf Stream sinks in the North Sea and off the southern coast of Greenland because large quantities of water evaporate into dry winds that blow across it; thus, its salt content rises and eventually it becomes denser than the water below. To balance the volume of water that moves north on the surface Gulf Stream, the sunken dense water flows south. The Gulf Stream won't sink if enough freshwater flows into the Gulf Stream; it doesn't become denser than the water below and hence could flip ocean currents to another pattern. The global climate warming fed by more greenhouse gases prompts more rainfall in the higher latitudes and makes Greenland's ice melt. Either of these events could dilute the Gulf Stream and prevent it from sinking.

Without the warming effect of the Gulf Stream, it is easy to understand why Europe would quickly get cold like North America. But why would the entire planet get colder? Although the reasons are uncertain, one model indicates that rearranging the ocean's circulation could lead to less evaporation in the tropics. Since water vapor is an important greenhouse gas, this decrease could cool the planet. Regardless of the mechanism, previous cold periods in Europe not only have been correlated with ocean current flips but also with global cooling. These facts and the possible connection between global warming and global cooling should be sobering for a world intoxicated on fossil fuels and intent on cutting forests.

Climate and human habitation are intimately connected. Releasing the vast quantities of carbon sequestered in fossil fuels will change the climate -- 250,000x10 to the 17 grams of carbon are trapped in natural gas, coal, petroleum, bitumen, and kerogen, while only 6.4x10 to the 17 grams of carbon as carbon dioxide are in the atmosphere. History tells us that earth's climate will change, however, forcing climate change by burning millions of years of stored sunshine in a few hundred years does not appear to be in our best, long-term interests.

The likely consequences of significant climate change -- dramatic acceleration of the on-going mass extinction, unpredictable fluctuations in agricultural yields, substantial flooding of coastal areas, increased ranges of parasites and diseases, more violent and extreme weather -- would affect all humankind and leave much of the burgeoning human population homeless and without the resources necessary for individual survival and civil order. In a fully populated world, displaced people would have nowhere to go or would fight to the death to acquire space already claimed. Territorial and ethnic conflicts of the worst kind -- like those we are already seeing in Africa and Eastern Europe -- would be common place. Certainly it is wise to plan for climate change because, even without human influence, it will come. At the same time, we are monumentally unwise to force climate change by radically altering the composition of the atmosphere."



FURTHER READING

Edward Bryant: CLIMATE PROCESS & CHANGE. Cambridge, UK:Cambridge University Press. 1997.
Ross Gelbspan: THE HEAT IS ON. New York: Addison-Wesley Publishing Co. 1997.
John Houghton: GLOBAL WARMING: THE COMPLETE BRIEFING. Cambridge, UK:Cambridge University Press. 1997.
Molly O'Meara: THE RISKS OF DISRUPTING CLIMATE. World Watch Magazine, November/December 1997, pp 10-24.
Clive Ponting: A GREEN HISTORY OF THE WORLD: THE ENVIRONMENT AND THE COLLAPSE OF GREAT CIVILIZATIONS. New York: Penguin Books. 1991.
Mathis Wackernagel and William Rees: OUR ECOLOGICAL FOOTPRINT: RELIEVING HUMAN IMPACT ON THE EARTH. Philadelphia: New Society Publishers. 1996.
Peter Ward: THE END OF EVOLUTION. New York: Bantam Books. 1994.
Edward O. Wilson: THE DIVERISTY OF LIFE. Cambridge, MA: Harvard University Press. 1992.
Edward O. Wilson: THE DIVERSITY OF LIFE (Book Excerpt). Discover, September 1992, pp 45-68.


ORGANIZATIONS

World Watch, 1776 Massachusetts Ave., NW, Washington, DC 20036.
Pew Center on Global Climate Change, 2111 Wilson Blvd., Suite 350, Arlington, VA 22201.





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Last modified: 09/09/02.
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