Volume: 03, Issue: 09 05/04/2005 
Clouds and the Earth Radiant Energy System measurements show reflected solar radiation (left) and emitted heat radiation (right). Image courtesy NASA.
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The energy balance of Earth refers to the amount of energy received from the sun (yellow arrows) minus the energy reflected and emitted from the Earth (red arrows). Image courtesy NASA.
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Methane is one greenhouse gas that impacts  energy balance on Earth. Image courtesy NASA.
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Other Articles in This Issue:
NASA Delays Shuttle Launch Window
Cassini Targets Unique Saturnian Moons
Florida Welcomes Mars Reconnaissance Orbiter
Send Your Students to Camp

Energy of Earth Is Out of Balance

Earth’s energy is out of balance, and it’s raising temperatures around the globe. Scientists have concluded more energy is being absorbed from the sun than is emitted back to space, causing the imbalance and ensuing warmer weather.

A recent study by scientists from NASA, Columbia University, and Lawrence Berkeley National Laboratory used satellites, data from buoys, and computer models to study Earth's oceans. They confirmed the energy imbalance by using precise measurements of increasing ocean heat content over the past 10 years.

Over the course of Earth’s history, the energy imbalances have been detected, but this particular instance is significant by average standards. The imbalance is 0.85 watts per meter squared, which will cause an additional warming of 1 degree Fahrenheit by the end of this century.

To understand the difference, think of a one-watt light bulb shining over an area of one square meter. Although it doesn't seem like much, adding up the number of feet around the world creates a big effect. To put this number into perspective, an imbalance of one watt per square meter, maintained for the past 10,000 years, is enough to melt ice equivalent to one kilometer of sea level, if there were that much ice.

"The energy imbalance is an expected consequence of increasing atmospheric pollution, especially carbon dioxide, methane, ozone, and black carbon particles,” said lead author Jim Hansen of NASA's Goddard Institute for Space Studies. “These pollutants block the Earth's heat radiation from escaping to space, and they increase absorption of sunlight."

As Earth warms it emits more heat. Eventually Earth will come back in balance, if the greenhouse gas emissions are kept at the same level as today. Scientists know it takes the ocean longer to warm than the land. The lag in the ocean's response has practical consequences, meaning an additional global warming of about one degree Fahrenheit is already in the pipeline. Even if there were no further increase of human-made gases in the air, climate would continue to warm that much over the next century.

Warmer world-wide water temperatures also affect other areas. If the ocean warms, ice could begin to melt more quickly and sea level could rise significantly during this century, according to Hansen.

Since 1993, sea levels have been measured by satellite altimeters. Data has shown they have risen by approximately 3.1 centimeters or 1.26 inches per decade. Although 3.1 centimeters is a small change, the rate of increase is twice as large as in the preceding century. There are positive feedbacks that come into play, as the area of ice melt increases. The researchers agree monitoring ice sheets and sea level is necessary to best ensure the system is in balance.

For more information and images, visit http://www.nasa.gov/vision/earth/environment/earth_energy.html .

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