The Science of Global Warming

Nearly everyone who enjoys the out-of-doors has noticed signs of global warming — milder winters, drier summers, fewer snowfalls, fiercer storms — but debate has raged over the cause: Is global warming a natural cycle that in time will reverse itself, or is human activity responsible for changing the climate?

Now scientific evidence demonstrates with a high degree of certainty that a buildup of greenhouse gases is warming the earth and changing the climate. Ice core samples prove that carbon dioxide concentrations are the highest in 400,000 years, and they are increasing at an unprecedented rate — 30 times faster than 10,000 to 20,000 years ago. And the evidence imputes human consumption of fossil fuels as the primary culprit of this dramatic increase.

Warming the Earth
By trapping heat from the sun near the planet’s surface, greenhouse gases, of which carbon dioxide (CO2) is the most prevalent, warm the earth. Before the advent of the industrial age, plants on land and in the oceans absorbed roughly the same amount of CO2 as was released from occurrences such as respiration, decomposition of plants and animals, volcanic eruptions and the burning of fossil fuels. Now, the escalating use of coal, gas and oil releases about 45 percent more CO2 than can be absorbed. The excess accumulates in the atmosphere where it remains for at least a century, capturing solar heat and warming the globe.

The Climate Connection
As atmospheric concentrations of greenhouse gases increase, the temperature of air, land and water rises. Because temperature influences components of weather such as water evaporation, rainfall and wind, global warming affects climate.

Scientists are able to paint a broad-strokes forecast of changes likely to occur, a forecast that improves in detail and precision as data collection increases, as interactions among climatic factors are more thoroughly understood and as climate modeling improves. Presently the scientific community consistently predicts the following climate changes will take place during the next century:

• Overall temperatures will warm, with the most dramatic changes occurring in high latitudes. North America could experience increases of as much as 10 degrees Fahrenheit by 2099.

• Warmer temperatures will decrease snowfall, thus diminishing reflective ground cover and reducing seasonal storage of water as snowpack, and increase rainfall, thereby augmenting runoff and stream flows and boosting the threat of floods.

• Warmer temperatures will speed the melting of glaciers and sea ice, which will freshen ocean waters and accelerate the worldwide rise of sea levels.

• Warmer oceans will alter weather patterns. For example, the El Niño phenomenon seems to originate in the central Pacific Ocean, where water temperatures have risen in concert with global warming. El Niño influences rainfall and temperatures over land and can cause droughts, floods, wet winters and other extreme weather events. Global warming may result in El Niño–like conditions and trends becoming semipermanent.

• Precipitation patterns will shift. Hurricanes and thunderstorms will occur with greater frequency and intensity. In some regions precipitation could increase by as much as 24 percent. In other places long seasons of unusually hot, dry conditions could shrink surface water and introduce extended droughts.