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Climate Change 101

The Greenhouse Effect

The climate we enjoy on earth is made possible due to a delicate balance of naturally occurring gases that trap some of the sun’s heat near the earth’s surface. This naturally-caused greenhouse effect is what keeps the earth’s temperature stable at an average of approximately 60°F—warm enough to support life as we know it . Without this natural greenhouse effect, our planet’s average temperature would be about 14°F and uninhabitable.

Global Warming: The Enhanced Greenhouse Effect

The problem we now face is that human actions have disturbed this natural balance by producing large amounts of some of these greenhouse gases (GHGs). The two greenhouse gases of most concern to local governments are carbon dioxide, or CO2, and methane.

Emissions of CO2 are produced whenever fossil fuels—such as oil, natural gas, gasoline, diesel fuel, and coal—are burned to produce electricity, heat buildings or power vehicles. Through daily energy- using activities, we are increasing the amount of CO2 in the atmosphere and magnifying the natural greenhouse effect. The net effect of this increased atmospheric concentration of CO2 and other GHGs is to trap more of the sun’s heat, causing the earth’s average temperature to rise—the phenomenon is known as global warming.

Methane is the second most important greenhouse gas resulting from human activities. Methane, or CH4, is a byproduct of organic waste and sewage decomposition. In urban areas, methane gas is produced as organic waste such as paper, yard trimmings, wood, and food waste decompose in landfills. Sewage treatment plants are also a significant urban source of methane. In terms of its greenhouse effect, methane is 21 times more powerful per unit than CO2.

Scientists around the world have studied and verified the increase in atmospheric changes and are in wide agreement that global warming is occurring and will have serious consequences for the entire planet. Research by an international panel of scientists has found that the average earth surface temperature has risen more than 1°F over the last 100 years. This temperature rise correlates with the increase in CO2 concentrations that has occurred in the past 150 years since the Industrial Revolution. Global changes in energy requirements due to industrialization and population increases, along with the dominant reliance on fossil fuels for that energy has increased the concentration of CO2 in our atmosphere by about 30%. Scientists predict that if atmospheric CO2 doubles from pre-industrial levels, average earth temperatures will rise by 2.3 to 7.2°F. According to a range of possible scenarios, this doubling of atmospheric CO2 could occur as early as 2050.

Why the Term Climate Change?

Since 1988, an international panel involving thousands of scientists from all over the world has led a comprehensive scientific assessment of these atmospheric changes, their potential impacts, and appropriate policy responses. This International Panel on Climate Change (also known as the IPCC) was jointly established by the World Meteorological Organization and the United Nations Environment Program. The work of these scientists is the largest and most comprehensive scientific effort on global warming undertaken to date.

Although the increase in greenhouse gases is causing an overall warming of the planet, scientists involved in the IPCC prefer the to use the concept of “climate change” to describe the consequences of this phenomenon.

The reason scientists feel that climate change is a more accurate term is that the increased levels of greenhouse gases in our atmosphere are causing climatic changes that vary across the planet, both from place to place and season to season. Even the slightest increase in average global temperature can cause major changes in climate patterns, resulting in more frequent and extreme weather events. Globally, while some regions may experience warming, other regions may become colder. Precipitation may increase in some regions, causing floods and mudslides, while decreasing in other regions, causing droughts water shortages.

Here in the U.S., we are already feeling climatic effects of more frequent and extreme weather events, mirroring the models developed by scientists. The period between 1995 and 1998 saw a record of 33 hurricanes. The recent Hurricane Floyd alone damaged 30,000 homes, killed 40 people and caused an estimated $1.3 billion in damages in North Carolina. Rain and snowfall have increased by 5% to 10% in the past 100 years—much of this increase being in the form of more frequent and intense downpours such as the heavy rainstorms in Ohio, Tennessee, and Mississippi that destroyed bridges and roads, and left hundreds of thousands of people without drinking water in 1997. For many areas in the U.S., droughts in 1998 were among the worst ever and 1999 had the driest growing season since the dust bowl. In 1999, parts of the country experienced persistent summer heatwaves, killing 257 Americans and thousands of cattle in July alone.

© 2000 ICLEI.

More information on the science of climate change is available at


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