Friday, June 06, 2008
Understanding global warming
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Marquita K. Hill
Hill, of Blacksburg, is retired from the University of Maine's Department of Chemical Engineering and is the author of "Understanding Environmental Pollution."
The author of the May 19 commentary "Global warming or cooling? Who knows?" lacks an understanding of global warming. First, the absorption of infrared radiation from the Earth by water vapor and carbon dioxide is -- up to a point -- natural. Otherwise, Earth would be too cold for life. What is now happening is very different.
Sherwood Thoele stated that "CO2 is heavier than air, so without air currents it won't rise above the ground." CO2 is heavier than air and can be trapped in caves or other enclosed spaces. However, CO2 released into the atmosphere does disperse homogeneously. The 2008 level of 387 parts per million CO2, measured at Mauna Loa observatory, Hawaii, varies only by a few ppm around the world.
That 387 ppm is only this year's figure as CO2 levels increase each year, and are now almost 40 percent higher than before humans started burning large quantities of fossil fuels. (And yes, there are good means of determining just what earlier levels of CO2 were.)
Under moist conditions, some CO2 does, as Thoele stated, form the weak acid, carbonic acid. This can be rained out, contributing to acid rain. However, the major contributors to acid rain, by far, are the much stronger sulfuric and nitric acids. Thoele says carbonic acid "helps release minerals in the soil ... making them available to plants." That sounds good. Unfortunately, in too many places, acids (predominately sulfuric and nitric) leach too many minerals from the soil, releasing them to be carried off in rainwater and depriving soils of essential nutrients, especially calcium and magnesium; some American forests suffer from this loss.
Carbon dioxide does come from burning fossil fuels -- natural gas, petroleum and, especially, coal -- and, to a lesser extent, from cement kilns. CO2 is the major contributor to the greenhouse effect. (However, when Thoele says "Major sources [of CO2] are fermenting (rotting) vegetation like in swamps," that is incorrect. Swamps are a source of methane, also a greenhouse gas, but much stronger than CO2. Swamps form methane naturally, but the higher-than-historic levels of methane we now see come from human action.)
He asks, "How does the infrared radiation from the sun get through the CO2/moisture [in our atmosphere] and wouldn't it already have absorbed as much infrared radiation as it could handle from the sun?" No. By far, most of the energy entering the Earth's atmosphere is not infrared, but rather shorter, more energetic wavelengths. It is primarily this more-energetic radiation that reaches and heats the Earth. This heat is then re-radiated as long-wave infrared, which can be trapped by greenhouse gases.
He says, "if there were a greenhouse effect from heat being blocked from leaving the Earth, then the temperature on cloudy days and at night shouldn't be so different than on a sunny day." However, look at the the greenhouse effect figure. Notice that only some of the infrared radiation from Earth is absorbed. But the major concern is that, as levels of greenhouse gases continue to rise, more and more of this infrared will be absorbed, leading to yet warmer temperatures.
What we see now is more than a warming spell. Earth's surface temperature has increased by about 1.4 degrees Fahrenheit. Moreover, much of that increase has occurred in the past three decades -- think about the rapid Arctic melting now being observed. As Thoele says, there are indeed "many variables that cause temperature changes." However, the fact that the temperature has increased over the past century has been demonstrated by exceedingly careful work done around the world.
Thoele says, "I submit that there is no manmade global cooling/warming, that there is no study or research data that makes a good argument to that effect." On the contrary, the quantity of good research data is overwhelming.
The Department of Defense has taken the climate change issue seriously, especially potential abrupt climate change, and commissioned a report: "National Security and the Threat of Climate Change." The report recommended that consequences of climate change be fully integrated into national security considerations.
Can those who are skeptical on the global warming issue likewise take the issue seriously enough to examine the rich information sources available to us?
