The Greenhouse Effect and Global Warming

How the Greenhouse Effect Works

Carbon dioxide (CO2) is an atmospheric constituent that plays several vital roles in the environment. It absorbs infrared radiation in the atmosphere. It plays a crucial role in the weathering of rocks. It is the raw material for photosynthesis and its carbon is incorporated into organic matter in the biosphere and may eventually be stored in the Earth as fossil fuels.

Most of the sun's energy that falls on the Earth's surface is in the visible light portion of the electromagnetic spectrum. This is in large part because the Earth's atmosphere is transparent to these wavelengths (we all know that with a functioning ozone layer, the higher frequencies like ultraviolet are mostly screened out). Part of the sunlight is reflected back into space, depending on the albedo or reflectivity of the surface. Part of the sunlight is absorbed by the Earth and held as thermal energy. This heat is then re-radiated in the form of longer wavelength infrared radiation. While the dominant gases of the atmosphere (nitrogen and oxygen) are transparent to infrared, the so-called greenhouse gasses, primarily water vapor (H2O), CO2, and methane (CH4), absorb some of the infrared radiation. They collect this heat energy and hold it in the atmosphere, delaying its passage back out of the atmosphere.

Due in part to the warming effects of the greenhouse gases, the global average temperature is about 15°C (59°F). Without the greenhouse gases the global average temperature would be much colder, about -18°C (0°F).

Greenhouse Gas Induced Global Warming

Since the industrial revolution got into full swing in the 19th century we have been burning ever increasing amounts of fossil fuels (coal, oil, gasoline, natural gas) in electric generating plants, manufacturing plants, trains, automobiles, airplanes, etc. Burning releases CO2 into the atmosphere (much the same as respiration does). These fossil fuels may have formed tens or hundreds of millions of years ago from the buried and preserved remains of plant and animal matter whose carbon originated via photosynthesis.

Sidebar: Photosynthesis - Respiration-Combustion

CO2 + H2O + sunlight -> CH2O + O2

O2 + CH2O -> energy + H2O + CO2

O2 + hydrocarbons -> energy + H2O + CO2

Photosynthesis and respiration in plants, animals, fungi, bacteria, etc. exchange carbon between the CO2 in the atmosphere and carbon compounds in organisms. But humans are now putting this natural carbon cycle out of balance. Because of the emission of CO2 long-stored in fossil fuels the percentage of CO2 in the atmosphere has increased from about 289 parts per million before the industrial revolution to over 360 parts per million and rising. Sometime during the 21st century the concentration of CO2 will be twice what it was before the industrial revolution.

With higher CO2 concentrations come expectations of a stronger greenhouse effect and therefore warmer global temperatures. This was originally proposed by a chemist named Arrhenius about a century ago. Global average temperatures have risen by a small, but measurable amount in the past 100 years, apparently in large part because of the higher level of atmospheric CO2. Global average temperatures are expected to be on the order of 2-5°C (3.6-9°F) higher by the time CO2 doubles the pre-industrial concentration. The temperature rise will be small in the tropics but much greater at high latitudes.

Consequences of Global Warming

A whole host of consequences will result. Some are probably already occurring.

Temperature measurements of the sea surface and deep ocean indicate that the oceans are warming. Rising ocean temperature causes rising sea level from thermal expansion of the water. Rising temperature also means melting glaciers and rising sea level through addition of meltwater to the oceans. Sea level rose about 1 foot during the last century, mostly from thermal expansion of the oceans. Sea level is expected to rise closer to 3 feet during the coming century. Rising sea level will cause increasing coastal erosion, flooding, and property damage during coastal storms on top of the potential for major loss of life from storms in low-lying coastal countries like Bangladesh and island nations in the Indian and Pacific Oceans.

Warmer sea surface temperatures will result in more and stronger tropical storms (hurricanes and typhoons). Coastlines already ravaged by these storms will expect to see more strong storms than before, increasing the loss of life and damage to infrastructure.

It is much more difficult to predict how regional and local weather patterns will change but there will certainly be changes. While higher temperatures will produce more rainfall across the globe, the regional rainfall patterns will likely change. Some areas will get more, some areas will get less. The timing of wet and dry periods may change. But higher temperatures will also mean more evaporation. Higher temperatures may also mean stronger storms with damaging winds. All of these mean new risks and changing conditions for agriculture. Centuries old farming practices will have to change. Some areas may go from being marginal to becoming a breadbasket region, while other regions may go from major agricultural production to marginal.

Higher CO2 allows plants to grow faster (more CO2 enhances photosynthesis). That would sound good for agriculture. However, weed species tend to grow even better than crop plants under enhanced CO2 conditions so improved crop growth may be nullified by weed competition.

Natural ecosystems will be hard pressed to keep up with the changing climate because the rate of change will be faster than typical long-term natural climate change. Many species, especially plant species, will not be able to migrate to cooler areas fast enough to keep up with the warming of their habitats. And arctic species will have no place to go and may not be able to adapt to the new conditions.

Severe summer heat in areas not used to it can lead to deaths. Higher heat and expansion of tropical areas may lead to increased incidence of malaria.

What Can We Do About Global Warming?

We can't realistically stop the rise of CO2 in the near term, but we can slow it and therefore reduce the consequences that will occur. More fuel-efficient cars, less frivolous driving, more use of mass transit, improved insulation to decrease the fuel burned to heat and cool our homes, more efficient appliances, use of fluorescent rather than incandescent light bulbs, and careful monitoring of home electricity usage (turn off the lights and TV when not using them) can reduce our energy needs. Conversion to alternatives like wind and solar power which don't burn fossil fuels and emit CO2 into the atmosphere. Planting large areas with trees will consume CO2 as the trees grow, until the forests mature. Stopping deforestation in the tropical forests around the world, especially in the Amazon and Indonesian rain forests, will keep that carbon in the forest rather than sending it back into the atmosphere as the trees are burned or decay and are not replaced by more. Other techniques have also been proposed such as the chemical removal of CO2 from smokestacks and burial in deep underground reservoirs, though only certain areas can benefit from this, or disposal in the deep ocean where they will form a semi-stable compound under the cold temperatures and high pressures, though the CO2 could too easily come bubbling back up. These latter solutions are not well studied and wouldn't be especially cheap.

Moreover, leaders, societies, communities, local planners, farmers, health organizations, need to recognize the changing climate and rising sea level as they make plans for the future. Our citizens need to be educated as to likely changes and how best to deal with the changing conditions.