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Posts Tagged ‘Simple Science and the Greenhouse’

Climate Change and the Greenhouse Effect

Wed ,12/08/2009

Most gardeners know how greenhouses work.  In the daytime, the sun’s radiation (visible and UV) comes in through the glass and warms the plants and soil.  The glass stops the heat radiation ( infrared ) from passing back through and the greenhouse stays warm enough to keep the plants from freezing, even at night. The Earth works pretty much the same way except there is no glass. Greenhouse gases, primarily water and  carbon dioxide, play the role of the glass and trap some of the radiation. Winter nights on Earth would be very cold without greenhouse gases.

Of the Sun’s energy coming to Earth, 30% is reflected immediately back into space by particles in the air, by clouds, and by the surface. Another 20% is absorbed by the atmosphere where it runs the weather cycle. The remaining 50% heats the land and oceans. All the absorbed heat is eventually radiated back into space as infrared radiation. It’s a balanced energy budget, 100% in and 100% back out. Anything that reflects more light back into space, such as an increase in particulate matter in the air, would cause the Earth to cool. Anything that delays the energy’s trip back to space, such as an increase in greenhouse gases, would cause the Earth to warm.

The best data we have clearly shows the Earth is getting warmer. NASA has compiled the Earth’s average temperature for each year since 1880 by using ships logs, weather stations, and satellite measurements. In the graph below , each square dot shows how far that year’s average temperature was above or below the 1970 value. The solid red line is the moving average, which makes the trend easier to follow.  Although the data varies widely from year to year, the trend is clearly upward.


http://data.giss.nasa.gov/gistemp/2007/ Credit: NASA/JPL/MSSS

The greenhouse effect links the temperature increase to man’s activities. The trend starts upward in about 1920. That was when the automobile, industrialization, and energy production began increasing the carbon dioxide concentration in the air. . The processes that remove carbon dioxide from the air take decades, so as the carbon dioxide concentration slowly built up, the Earth became a better greenhouse. The concentration of carbon dioxide in the air is now 50% higher than in 1920 and the Earth’s temperature is about 0.8°C (or 1.3 °F) higher. No natural occurrences such as volcanoes, sunspots, fires, or dust storms can account for the major trend in the data.