2. Global Warming

Humans are pumping increasing amounts of carbon dioxide into the air

Fig. .. 

For hundreds of years, humans have been filling the sky with carbon dioxide. The invisible waste gas is dumped into the air by burning fossil fuels – coal, oil and natural gas. When these materials are burned, their carbon atoms, denoted C, enter the air and combine with oxygen atoms, O, or oxygen molecules, O2, to make carbon dioxide, abbreviated CO2.

Every time we drive a car, use electricity from coal-fired power plants, or heat our homes with oil or natural gas, we release carbon into the lower atmosphere. The burning of forests, whose trees hold much carbon dioxide, has also contributed.

Just a few decades ago, no one knew if any of the carbon dioxide stayed in the atmosphere or if it was all being absorbed in the oceans. Then in 1958 Charles D. Keeling (1928-) began measurements of its abundance in the clean air at the Mauna Loa Observatory in Hawaii. It is located at a remote high-altitude site in the midst of a barren lava field, far from cars and people that produce carbon dioxide and from nearby plants that might absorb it.

The sensitive measurements showed that the amount of carbon dioxide in the atmosphere increases and decreases in an annual cycle. Every spring plants bloom, sucking CO2 out of the air, and every fall CO2 is released back into the air as plants either decay or lose their leaves. The measurements had recorded the breathing of the plants all over the Northern Hemisphere.

But more importantly, Keeling’s measurements showed that humans are also changing the composition of the atmosphere. Superimposed on the annual fluctuations, there was a systematic increase over the entire period of observation, continuing nonstop since 1958 (Fig. GW.1). Year by year the total measured concentration of carbon dioxide grew, as inexorably as the expansion of the world’s population and human industry.

Since 1958, atmospheric concentrations of CO2 have increased from 315 parts per million (106), abbreviated 315 ppm, to 365 ppm at the turn of the century.

Studies of ice deposits in Antarctica indicate that the amount of CO2 has been increasing at an exponential rate ever since the beginning of the industrial revolution in the mid-18th century. Air bubbles that are trapped in the ice act like time capsules, conserving the atmosphere of the past. The air has been sealed off in the bubbles when the ice was laid down, and extracted from cores drilled deep within the layered ice deposits. The ice cores show that the concentrations of the gas averaged 280 ppm just before the industrial era. In the succeeding two and a half centuries, a mere blink in the eye of cosmic time, the atmospheric concentration of carbon dioxide has increased 31 percent.

The atmosphere now contains almost 800 billion tons of carbon dioxide. Humans continue to release about 7 billion tons of it each year. In other words, each person on Earth is, on average, dumping about a ton of carbon dioxide into the air every year, and there is no end in sight. (The world population in January 2002 was 6.202 billion, increasing at the rate of about 6 million people every month.)

Once added to the air, carbon dioxide spreads throughout the entire atmosphere. And it remains in the air for a long time, taking decades and even centuries to disappear. So future generations will have to contend with our present activities.

Since the oceans cover three-quarters of the Earth’s surface, they can absorb great quantities of the carbon dioxide, eventually taking up about half of the amount that is released into the atmosphere by burning coal and oil. In the meantime, not all of the gas stays in the air. Some of it circulates through the atmosphere in one of nature’s grand, known as the carbon cycle.

During the spring and summer, trees and other vegetation take in carbon dioxide from the atmosphere, incorporating some of the carbon into the plant tissue and releasing oxygen into the air. Animals breathe the oxygen and return carbon dioxide to the atmosphere. Plants release some carbon when their leaves fall and decay in the autumn, and when the plants die they also sequester carbon in the soil.

Every year, roughly half of the heat-trapping gas remains in the air, building up over the decades and centuries. But why should adding such small amounts of an invisible, nontoxic gas be a cause of concern? The total amounts are miniscule, but their consequences are significant. Even relatively small amounts of the gas can warm the Earth by the greenhouse effect, perhaps affecting the climate.

Roger Revelle (1909-1991) and Hans E. Suess (1909-1993) realized the threat decades ago. They argued that the oceans might not readily absorb all of the carbon diode being released into the air, and that the amount of atmospheric CO2 would steadily increase as the fuel and power requirements of our worldwide civilization continued to rise. With prophetic insight, they wrote in 1957 that:

“Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future. Within only a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years. This experiment, if adequately documented, may yield a far-reaching insight into the processes determining weather and climate.”

As subsequently documented by Charles Keeling, we are indeed altering the composition of our air in a unique global experiment.

Many scientists now think that humans are not only altering the composition of the atmosphere, but that the greenhouse effect of the increased amounts of CO2 will alter the climate and weather. They also now realize that other greenhouse gases are being released into the atmosphere as the result of human activity, and that they additionally contribute to global warming and possible climate change.

(page 2 of 9)

Copyright 2010, Professor Kenneth R. Lang, Tufts University