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Global warming and greenhouse gases

This lesson is from: Climate Kids.
Earth Science Communications Team at NASA’s Jet Propulsion Laboratory / California Institute of Technology

What is a greenhouse?

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A greenhouse is a house made of glass. It has glass walls and a glass roof.

People grow tomatoes and flowers and other plants in them. A greenhouse stays warm inside, even during winter.

Sunlight shines in and warms the plants and air inside. But the heat is trapped by the glass and can’t escape.

So during the daylight hours, it gets warmer and warmer inside a greenhouse, and stays pretty warm at night too.

How is Earth like 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.

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.
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If the greenhouse effect is too strong, then Earth gets warmer and warmer.

This is what is happening now. Too much CO2 and other greenhouse gases in the air are making the greenhouse effect stronger.
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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.

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A forest burns. (Photograph copyright Woods Hole Research Center).

The ocean also absorbs a lot, but not all, of the excess carbon dioxide in the air.

Unfortunately, the increased carbon dioxide in the ocean changes the water, making it more acidic.

Ocean creatures don’t like acidic water.

The bleached out, unhealthy coral in this picture is just one example of what acidic water can do.

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Coral Bleaching – Great Barrier Reef

The Great Barrier Reef has experienced a number of masses of coral bleaching events which occurred in 1998 and again in 2002. The coral was a lot more severe in 2002, when surveys showed almost 60% of the reefs experienced bleaching of some degree throughout the bleaching.

The Great Barrier Reef, on the coast of Australia experienced bleaching events in 1980, 1982, 1992, 1994, 1998, 2002 and 2006.

{ http://greatbarrierreefconsequences.weebly.com/coral-bleaching.html }

Coral Bleaching - Great Barrier Reef


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.

“The Blue Marble from Apollo 17, NASA”

Water in the clouds holds in some of the heat from Earth’s surface.

But the bright white tops of clouds also reflect some of the sunlight back to space.

So with clouds, some energy from the Sun never even reaches Earth’s surface.

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.

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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?
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[ At night, clouds trap some of the heat from Earth’s surface. Thus, it does not escape back into space. ]

Or, since more water vapor means more clouds, will the fluffy white clouds reflect enough sunlight back into space to make up for the warming?
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[ During the day, clouds reflect the Sun’s energy back to space, before it has a chance to heat Earth’s surface. ]

This cloud riddle has scientists scratching their heads and trying to figure it out.

NASA is helping with satellites like Aqua and CloudSat, which study the Earth’s water cycle and clouds in 3-D.

greenhouse 10 CLOUDSAT_3dPrapiroon_eye

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.


Dimming the SUN PBS

“Dimming the Sun” investigates the discovery that the sunlight reaching Earth has been growing dimmer, which may seem surprising given all the international concern over global warming. At first glance, less sunlight might hardly seem to matter when our planet is stewing in greenhouse gases. But the discovery of global dimming has led several scientists to revise their models of the climate and how fast it’s changing. According to one recent and highly controversial model, the worst-case warming scenario could be worse than anyone has predicted. “Dimming the Sun” unravels this baffling climate conundrum and the implications for Earth’s future.

To find out what global dimming means for the fate of the planet, NOVA reports on the findings of the world’s top climate detectives, including an American scientist who found a grim but crucial opportunity immediately following September 11, 2001, when the entire U.S. airline fleet was grounded for three days. This presented a unique opportunity to study the effects of airplane vapor trails on the atmosphere (see The Contrail Effect). Comparing changes in the daily temperature range showed that the absence of dimming from aircraft pollution alone made a marked difference to the temperature. This result hints at how much the effects of atmospheric pollution had been underestimated.

Working in Israel, Dr. Gerald Stanhill was one of the first to discover the surprising fact that less solar energy is reaching the Earth’s surface. While his measurements were met with skepticism, a review of worldwide data by Stanhill and a German researcher demonstrated that during the 1980s and early ’90s, sunlight reaching Earth’s surface had dropped just about everywhere. Halfway around the world, independent studies by Australian scientists confirmed this disturbing diagnosis. (For more, see Discoveries in Global Dimming.)

Scientists have long known that increasing air pollution—the smog that clouds urban skies—endangers our respiratory health. But they had underestimated the impact of pollution on the amount of sunlight reaching Earth. Some scientists now believe that global dimming may also disturb rainfall patterns such as the Asian monsoon. If they are right, global dimming may be one of many factors that contributed to severe droughts and famines in Africa during the 1980s.

The good news is that pollution controls have slowed and possibly even halted global dimming during the last decade. The bad news—and the ironic twist in NOVA’s story—is that without pollution, more sunlight is reaching Earth, revealing the full impact of global warming. Although all climate models have important uncertainties, the unsettling implication is that, with dimming fading away in many regions, global temperatures may rise even faster than most models have predicted.

XKCD Global Warming because what used to be nomal now feels too cold

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