The Natural and Enhanced Greenhouse Effect

In this "greenhouse environment," it is the combination of water vapor and trace gases that are responsible for trapping the heat radiated from the Sun. The natural amount keeps the Earth habitable. Without this trapped warmth, the Earth would have an average temperature of -0.4°F (-18°C). If this were the case, the Earth would look much different-there would most likely be very little, if any, liquid water available. The entire Earth would have an ecosystem similar to that of the harshest areas in Antarctica.

The Earth's natural greenhouse effect is critical for the survival and diversity of life. Since the Industrial Revolution (over the past 250 years or so), the natural greenhouse effect has been augmented by human interference. CO2, one of the atmosphere's principal greenhouse gases, has been altered to such an extent by human activity that the natural greenhouse effect is no longer in balance. The Earth's energy balance now must contend with what is referred to as the "enhanced greenhouse effect" or "anthropogenic greenhouse warming." CO2 is being added in voluminous amounts as a result of human activity; deforestation; agricultural practices; the burning of fossil fuels for transportation; urban development; heating and cooling homes; and industrial processes.

CO2 in the atmosphere has increased 31 percent since 1895. Concentration of other greenhouse gases, such as methane and nitrous oxides (also related to human activity) have increased 151 percent and 17 percent, respectively.

This enhanced greenhouse effect began in the age of the Industrial Revolution of the 1700s. At that time, CO2 content in the atmosphere was 280 parts per million (ppm). By 1958, it had increased to 315 ppm; by 2004, 378 ppm; by 2005, 379 ppm; and by 2007, 383 ppm. According to James E. Hansen, a world-renowned expert on global warming and climate change in New York at NASA's Goddard Institute for Space Studies (GISS), "Climate is nearing dangerous tipping points. We have already gone too far. We must draw down atmospheric CO2 to preserve the planet we know. A level of no more than 350 ppm is still feasible, with the help of reforestation and improved agricultural practices, but just barely—time is running out."

Although not the only greenhouse gas, CO2 does seem to be the one most focused on because it is one of the most important and prevalent. It makes up about 25 percent of the natural greenhouse effect. It is so prominent because there are several natural processes that put it in the atmosphere, such as the following:

• Forest fires: When trees are burned, the CO2 stored within them is released into the atmosphere.

• Volcanic eruptions: CO2 is one of the gases released in abundance by volcanoes.

• Oceans: Oceans both absorb and release enormous amounts of CO2. Historically, they have served as a major storage facility of CO2 put into the atmosphere from human sources. Recently, however, scientists at NASA and NOAA have determined that the oceans have become nearly saturated and are approaching their limits as a carbon store.

• Trees, plants, grasses, and other vegetation serve as significant stores of carbon. When they die and decompose, half of their stored carbon is released into the atmosphere in the form of CO2.

• When vegetation dies, the other half of their stored carbon is absorbed by the soil. Over time, some of this carbon is released into the atmosphere as CO2.

• Any life-form that consumes plants that contain carbon also emit CO2 into the atmosphere through breathing. This includes animals, insects, and even humans.

With all this CO2 finding its way into the atmosphere, fortunately there are some processes that help keep it in check. Plants and trees remove CO2 from the atmosphere through photosynthesis (turning the Sun's energy into food). The oceans absorb large amounts of CO2; and phy-toplankton (tiny organisms that float in the ocean) also take in CO2 through photosynthesis.

Ideally, keeping CO2 in balance is desirable, but throughout the Earth's history, this has not always been possible. When CO2 levels have dropped, the Earth has consistently experienced an ice age. Since the last ice age, the CO2 levels have remained fairly constant, however, until the Industrial Revolution, when billions of tons of extra CO2 began to be added to the Earth's atmosphere.

The turning point was the use of fossil fuels—coal, oil, and gas. These fuels are made from the carbon of plants and animals that decomposed millions of years ago and were buried deep under the Earth's surface, subjected to enormous amounts of heat and pressure. When this carbon is converted into usable energy forms and is burned as a fuel, the carbon combines with oxygen and releases enormous amounts of CO2 into the atmosphere.

According to NASA/GISS, CO2 levels have not been as high as they are today over the last 400,000 years. The enhanced greenhouse effect has not come as a surprise to climate scientists, other experts, and decision makers, however. In addition to being addressed by Fourier, Arrhe-nius, and Callendar, another climate giant, Charles David Keeling of the Scripps Institution of Oceanography, made enormous strides in establishing the rising levels of CO2 in the Earth's atmosphere and the subsequent issue of the enhanced greenhouse effect and global warming.

Keeling set up a CO2 monitoring station at Mauna Loa, Hawaii, in 1957. Beginning in 1958, Keeling made continuous measurements of CO2, which still continue today. He chose the remote Mauna Loa site so that the proximity of large cities and industrial areas would not compromise the atmospheric readings he was collecting. Air samples at Mauna Loa are collected continuously from air intakes at the top of four 23-foot (7 m) towers and one 89-foot (27 m) tower. Four air samples are collected each hour to determine the CO2 level.

The measurements he gathered show a steady increase in mean atmospheric concentration from 315 parts per million by volume (ppmv) in 1958 to more than 383 ppmv by 2007. The increase is considered to be largely due to the enhanced greenhouse effect and the

The world's first functioning CO2 monitoring station, initiated by Charles Keeling, is atop Mauna Loa, the highest mountain on Hawaii. Here scientists are able to monitor atmospheric CO2 levels. This is a good place to measure CO2 levels because it is far away from major cities, where large amounts of air pollution could interfere with the results. This facility has been instrumental in determining that CO2 levels are rising; the resultant graph from the continual monitoring since 1957 is one of the most well-documented pieces of evidence supporting global warming. (NOAA)

burning of fossil fuels and deforestation. This same upward trend also matches the paleoclimatic data shown in ice cores obtained from Antarctica and Greenland. The ice cores also show that the CO2 concentration remained at approximately 280 ppmv for several thousand years, but began to rise sharply at the beginning of the 1800s.

The Keeling Curve also shows a cyclic variation of about 5 ppmv each year. This is what gives it the "sawtooth" appearance. It represents the seasonal uptake of CO2 by the Earth's vegetation (principally in the Northern Hemisphere because that is where most of the Earth's

Collected since 1958, the Keeling Curve has been instrumental in providing convincing evidence that CO2 levels are rising worldwide. The blue line depicts the readings collected from the Mauna Loa observation station, and the red line depicts data collected from the South Pole. Without this continuous data, it would be much more difficult to determine the existence of global warming.

vegetation is located). The CO2 lowers in the spring because new plant growth takes CO2 out of the atmosphere through photosynthesis; and it rises in autumn as plants and leaves die off and decay, releasing CO2 gas back into the atmosphere.

Mauna Loa is known today as the premier long-term atmospheric monitoring facility on Earth. It is also considered one of the world's most favorable locations for measuring undisturbed air because vegeta tion and human influences are minimal and any influence from volcanic vents have been calculated and excluded from the measurement. The methods and equipment used to create the continuous monitoring record have been the same for the past 50 years, so the monitoring program is highly controlled and consistent.

According to the Carbon Dioxide Research Group of the Scripps Institution of Oceanography, "Because of the favorable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentrations of atmospheric CO2 in the middle layers of the troposphere."

Charles Keeling was a true pioneer in establishing the existence of global warming. His work was instrumental in showing scientists worldwide that the CO2 level in the atmosphere was indeed continually rising. This was the first strongly compelling evidence that global warming not only existed, but was accelerating. Because of the worthwhile merits and significance of his work, NOAA began monitoring CO2 levels worldwide in the 1970s. There are currently about 100 sites continuously monitored today because of what was started on Mauna Loa.

The Keeling Curve has now celebrated its 50th anniversary of continuous collection, representing the world's longest continuous record of atmospheric CO2 levels. This single curve is what provided the first compelling evidence that atmospheric CO2 levels have been rising since the middle of the 20th century. Ralph Keeling, Charles Keeling's son, says, "The Keeling Curve has become an icon of the human imprint on the planet and a continuing resource for the study of the changing global carbon cycle. Mauna Loa provides a valuable lesson on the importance of continuous Earth observations in a time of accelerating global change."

The Intergovernmental Panel on Climate Change (IPCC) has projected that with continued global warming, temperatures will rise an average of 2.3-9.7°F (1.4-5.8°C) in the next 100 years. Polar region temperatures, however, are expected to rise more than the average. Winter temperatures over land could rise as much as 4.2-23.3°F (2.5-14°C) above current normal temperatures. This could happen because of a change in surface albedo. Currently, with much of the polar areas being covered by snow and ice, they have a high albedo, so much of the insolation is reflected back to space. As temperatures warm, however, the snow and ice will melt, exposing darker surfaces (land and water), which will naturally absorb more heat, which will melt more ice and uncover more dark surface area. This could continue in a cycle until all the snow and ice are melted, greatly changing the heat balance in the polar regions, causing a rapid warming.

Was this article helpful?

0 0
Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment