What is a greenhouse?
A greenhouse is made of glass. It traps the Sun's energy inside and keeps the plants warm, even in winter.
How is Earth a greenhouse?
Earth's atmosphere does the same thing as the greenhouse. Gases in the atmosphere such as carbon dioxide do what the roof of a greenhouse does. During the day, the Sun shines through the atmosphere. Earth's surface warms up in the sunlight. At night, Earth's surface cools, releasing the heat back into the air. But some of the heat is trapped by the greenhouse gases in the atmosphere. That's what keeps our Earth a warm and cozy 59 degrees Fahrenheit, on average.
Greenhouse effect of Earth's atmosphere keeps some of the Sun's energy from escaping back into space at night.
Is it warm in here, or is it just me?
You might think 59 degrees Fahrenheit is pretty cold. Or, you might think that's warm. It depends on what you are used to. That temperature would melt all the Arctic ice. Yes, it's colder than 59 degrees in a lot of places, and hotter than 59 degrees in a lot of places, but 59 is the average of all of the places.
If the atmosphere causes too much greenhouse effect, Earth just gets warmer and warmer.
Every place has its own climate, whether Arctic cold, tropical warm, or
something in between. Averaging them all together makes global climate.
Why can't we just plant more trees?
You might well wonder, because, after all, trees—like all plants—take in carbon dioxide and give off oxygen.
Well, that might help a little. But, instead of planting more forests, some people are cutting them down and burning them to make more farm land to feed the growing human population.
A forest burns. (Photograph copyright Woods Hole Research Center).
These coral are sick. They should be colorful, not bleached out.
Don't clouds keep Earth cooler?
Water in the atmosphere also acts as a greenhouse gas. The atmosphere contains a lot of water. This water can be in the form of a gas—water vapor—or in the form of a liquid—clouds. Clouds are water vapor that has cooled and condensed back into tiny droplets of liquid water.
Earth's clouds as seen from space.
How much the clouds affect the warming or cooling of Earth's surface is one of those tricky questions that several NASA missions are aiming to answer.
Clouds prevent some of the Sun's energy from ever reaching Earth's surface.
Or do clouds make Earth warmer?
Here is a riddle—a serious one, not a joke:As the ocean warms up, more water evaporates into the air. So does more water vapor then mean more warming? And does more warming mean more water vapor? And ‘round and ‘round we go?
At night, clouds trap some of the heat from Earth's surface. Thus, it does not escape back into space.
During the day, clouds reflect the Sun's energy back to space, before it has a chance to heat Earth's surface.
The top image is a hurricane, as seen by a satellite.
Below is a cross-section of the storm clouds. This colorful image was
made with data from the CloudSat satellite. It shows with different
colors how much water is contained in the clouds at different heights.
Visit: http://climatekids.nasa.gov/greenhouse-effect/ in order to learn more.
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