Climate change and your health

The debate is over; nearly all scientists (and politicians) agree that climate change is real, is here, and is the result of human activity. Experts also agree that the consequences of global warming are serious and far reaching. All too often, though, these consequences are framed in terms of the threat to polar bears, exotic wildlife, and beautiful glaciers. Without minimizing the value of stately bears and snow-covered peaks, many people find it hard to make lifestyle changes and economic sacrifices to protect such distant assets. But climate change threatens more than the earth's vistas. It also threatens human health — and it's already causing problems here in the United States.

Our planetary greenhouse

Sunshine warms the earth. When solar radiation enters the atmosphere, a portion is bounced back into space, and another portion is absorbed by clouds and water vapor, but the majority strikes the planet's surface. This solar energy warms the earth, but it's also reflected back into the atmosphere in the form of infrared radiation. Some of the infrared penetrates through the atmosphere into space, but some bounces off atmospheric gases and heads back to earth, where it adds warmth (see figure).

The atmospheric gases that reflect infrared radiation back to earth are known as greenhouse gases. Without them, too much solar energy would be lost, and the earth would be ice cold. But since the industrial revolution, the concentration of atmospheric greenhouse gases has increased, and the increase has accelerated in the past 50 years. That means more infrared energy is reflected back to earth, where it produces global warming. Scientists report that the earth's temperature increased by 0.6° C (1.1° F) during the 20th century, and they project an additional rise by as much as 4.4° C (6.1° F) during this century.

Greenhouse gases

Heat-trapping greenhouse gases are formed on earth by natural processes and human activities and then enter the atmosphere. Here is a primer on the major gases:

Carbon dioxide (CO2). A tiny amount of CO2 enters the atmosphere every time you breathe out. But the CO2 produced as a waste product of the body's metabolism is dwarfed by the CO2 generated when wood and fossil fuels such as oil, natural gas, and coal burn. A variety of other industrial reactions also produce CO2. Plants remove CO2 from the air as part of the biological cycle. But as fossil fuel combustion has increased and the world's forests have shrunk, atmospheric CO2 climbed from about 280 parts per million (ppm) in 1750 to 315 ppm in 1958, and then to today's level of nearly 380 ppm. Carbon dioxide bears much of the blame for global warming — and at the rate we're going, atmospheric CO2 levels could double as early as 2050.

Methane. Like CO2, methane is emitted during the production and transport of oil, gas, and coal. But methane also enters the air from the gastric emissions and "tailpipe" of cattle and from decomposing manure and organic wastes in solid-waste landfills. The concentration of methane in the atmosphere has more than doubled since the industrial revolution.

Nitrous oxide. This gas enters the atmosphere from agricultural and industrial activity, including fossil fuel combustion.

Fluorinated gases (halocarbons). All fluorinated gases result strictly from human industrial activities, not natural sources. Although only tiny amounts are present in the atmosphere, they are very potent greenhouse gases.

While all of these gases contribute to worrisome global warming, CO2 and methane are particularly concerning. And since CO2 lingers in the atmosphere for 50 to 200 years and methane for 12 years, prompt action is needed to control gas emissions, mitigate global warming, and protect human health.