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Global Warming.


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What is Global Warming?

sun.jpg, photo courtesy of NOAA Photo Library
The term Global Warming refers, without any implications for the cause or magnitude, to the observation that the atmosphere near the Earth's surface is warming. This warming is one of many kinds of climate change that the Earth has gone through in the past and will continue to go through in the future.

Why is Global Warming important?

Temperature increases will have significant impacts on human activities, including: where we can live, what food we can grow, how and where we can grow food, and where organisms we consider pests can thrive. To be prepared for the effects of these potential impacts we need to know how much the Earth is warming, how long the Earth has been warming, and what has caused the warming. Answers to these questions provide us with a better basis for making decisions related to issues such as water resources and agricultural planning.

What is the Greenhouse Effect?

Greenhouse effect image Our planet absorbs radiant energy from the sun and emits some of that energy back to space. The term greenhouse effect describes how water vapor, carbon dioxide, and other "greenhouse" gases in the atmosphere alter the return of energy to space, and in turn, change the temperature at the Earth's surface. These greenhouse gases absorb some of the energy that is emitted from the Earth's surface, preventing this energy from being lost to space. As a result, the lower atmosphere warms and sends some of this energy back to the Earth's surface. When the energy is "recycled" in this way, the Earth's surface warms.

Life on Earth would be very different without the greenhouse effect. The greenhouse effect keeps the long term annual average temperature of the Earth's surface approximately 32°C (or about 58°F) higher than it would be otherwise.

How is the Greenhouse Effect related to Global Warming?

Greenhouse gases occur naturally in the Earth's atmosphere, but are also being added by human activities. This happens primarily through the burning of fossil fuels, such as coal, oil and natural gas, which releases carbon dioxide to the atmosphere. Over the past century, atmospheric carbon dioxide (as measured from ice cores) has increased due to human activities from 300 to 380 parts per million (ppm), and the average Earth temperature has increased approximately 0.7°C (or about 1.3°F).
Co2 image
Given what we know about the ability of greenhouse gases to warm the Earth's surface, it is reasonable to expect that as concentrations of greenhouse gases in the atmosphere rise above natural levels, the Earth's surface will become increasingly warm. Many scientists have now concluded that global warming can be explained by a human-caused enhancement of the greenhouse effect.

It is important to remember both that the greenhouse effect occurs naturally, and that it has been intensified by humankind's input of greenhouse gases into the atmosphere.

Are Ozone Holes related to Global Warming or the Greenhouse Effect?

ozone.gif, photo courtesy of NASA The formation of ozone holes is related to these scientific issues, yet is still distinct.
Ozone plays a very important, natural role in the upper atmosphere (called the stratosphere), where 90% of it exists. Stratospheric ozone acts as a shield against harmful ultraviolet (UV) radiation from the sun. This ozone can be destroyed by human-produced chemical compounds called chlorofluorocarbons, or CFCs. When these CFCs are combined with extremely cold stratospheric temperatures over the poles, solar radiation, and particular patterns of atmospheric circulation, chemical reactions occur that cause "Ozone Holes" over Antarctica (pictured above) and the Arctic.

The formation of ozone holes is related to global warming and the greenhouse effect in two ways. First, CFCs are greenhouse gases. Thus, the release of these compounds into the atmosphere will have two separate effects: to destroy ozone and to add to the greenhouse effect. Second, if stratospheric temperatures or patterns of atmospheric circulation change as part of global warming, this will affect the chemical reactions that destroy ozone and cause the ozone holes to either grow or shrink.
daily ozone image
For daily updated images of the ozone, please visit NOAA's Stratosphere: SBUV-2 Total Ozone Page with images of the ozone from the NOAA-14 Satellite by clicking here or on image at left.

On to... "How do we study global warming?"
Back to... "The Story"

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Last Updated Wednesday, 20-Aug-2008 11:23:45 EDT by paleo@noaa.gov
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