The greenhouse effect
The gases in the atmosphere that help retain heat are called greenhouse gases. These gases, primarily carbon dioxide (CO2), absorb heat instead of allowing it to escape into space. This "greenhouse effect" makes the planet a hospitable place.
However, greenhouse gases can have negative effects, too. Human activity has increased the amount of CO2 in the atmosphere. Since the 1800s, industrialized societies have burned fossil fuels such as coal, oil, and natural gas; these processes all give off CO2. During the past 25 years, the amount of CO2 in the atmosphere has increased by about 8 percent. With more CO2 in the atmosphere, more heat is absorbed and retained, causing global temperatures to rise.
Some scientists project that by the next century, CO2 levels in the atmosphere could be twice what they are today, causing a global temperature increase of about 3 degrees. Three degrees may not seem like much, but even a few degrees can have serious consequences. Tropical diseases could increase, since mosquitoes and other disease-carrying insects thrive in a warmer climate. Sea levels could rise, and coastal cities such as New Orleans and Washington, D.C., could be battered by storm surges. Prosperous farmland could dry up and agricultural regions could shift, wreaking havoc on the global economy.
It is possible that the recent warming trend is due more to natural cycles of cooling and warming than to human activity. Global climate change occurs on a scale of tens or hundreds of thousands of years, but scientists have only begun to study these effects in the last 150 years. Still, most scientists agree that just as climate affects our lives, we can affect the climate. Just how much we can influence it remains to be seen.
i didnt no that either but now i do
snapdropsix Community Member 
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