Environmental Horticulture. Greenhouse Effect


The greenhouse effect is a term that describes an increase of the average global temperature and is often associated with global warming which is the subject of great debate and concern worldwide. Although warnings about the human generated causes of an enhanced greenhouse effect and the subsequent catastrophic outcomes have been sounded for over 100 years, global warming has only recently become an important political matter, at least in the U.S. President Bush, for the first time in his term of office, referred to the subject in his State of the Union speech last month. Even then, he chose his words carefully by calling this phenomenon, ‘global climate change.’ This discussion will first define the greenhouse effect then explain how naturally occurring and man-made gases affect it along with examples of the consequences of these forces.


Essentially, the greenhouse effect functions in the following manner. When sunlight pierces the atmosphere and hits the earth’s surface, not all of the sun’s solar energy is absorbed. Approximately a third of it is reflected back into space. Specific atmospheric gases serve in much the same way as does the glass of a greenhouse, thus the terminology. These gases allow sunlight to penetrate then trap some of the solar energy which heats the earth (Breuer, 1980). It is a delicate balance and because these greenhouse gases have been artificially augmented by man-made sources, more build up in the atmosphere has occurred thus trapping more of the sun’s energy and reflecting less back in to space. This occurrence is causing the earth to warm.

Carbon Dioxide (CO2) is the most prevalent of the greenhouse gases. Trees absorb CO2 and when they die, CO2 is restored to the atmosphere. The clearing of forests by mass burning, which is happening at a phenomenal rate in the tropical rain forests, is decreasing the amount of CO2 that is absorbed and increasing the amount that is added to the atmosphere. CO2 supplies about half of the total gases that create the greenhouse effect (Breuer, 1980). Since 1970, at least 20 per cent of Amazon rainforest has been lost from deforestation. This figure could be under-representative because it does not include trees that have been felled by selective logging techniques which are less noticeable than clear-cutting yet causes considerable harm. Ecologists and scientists warn that another 20 per cent will be lost within the next 20 years. If this were to occur, the ecological system that sustains the forest and thus the planet’s weather patterns will start to disintegrate. The rising temperature of the Earth, due to global warming, will exacerbate the situation and cause droughts which will lead to massive wildfires in the region. Instead of life-giving oxygen which is now furnished by the lush rainforests, the fires will expel great amounts of carbon dioxide into the atmosphere. Given this very real and impending scenario, it is difficult to imagine how the human race along with all other life on earth could continue to live. Today, the greenhouse gases emitted from Brazil ranks near the world’s top polluter, the U.S., because of the slash-and-burn techniques used to clear the rainforest.

Although deforestation is contributing heavily to the excess of CO2 in the atmosphere, a larger portion is caused by the burning of fossil fuels such as oil and coal. Fossil fuels are burned by factories, vehicles and electricity-producing power plants to name a few sources. The vast majority of this excessive fuel consumption and its poisonous, pollutant and greenhouse-enhancing byproducts are located in the U.S., Europe and Russia (Breuer, 1980).

Other greenhouse gases include methane, which is released when vegetation is burned during land clearing, during oil exploration activities and the coal-mining process; chlorofluorocarbons (CFCs), which is the substance that cools refrigerators and provides the propulsion in aerosol cans and nitrous oxide (N2O) which is the lesser cause of CO2 (Breuer, 1980). It is generated from both man-made and natural processes. It is estimated that man-made influences represents about half of the CO2 output. Much as the global warming issue, whose destiny is tied to deforestation, even if climate change due to carbon monoxide emissions were proved a myth, reducing air pollution still makes sense.

Simply stated, if immediate action is not taken to reverse the present trend of deforestation, the immense Amazon rainforest will soon become a desert region not unlike the Sahara in Africa. Once this process is underway, the effects are irreversible. Some scientists believe the transformation from forest to desert could begin as early as this year. Studies have determined that the Amazon rainforest, even in its current state, could not withstand three years of drought conditions without beginning the irrevocable path to becoming the Amazon desert. This result, in and of itself, is tragic enough but the repercussions to the rest of the world would be as catastrophic. “Scientists say that this would spread drought into the northern hemisphere, including Britain, and could massively accelerate global warming with incalculable consequences, spinning out of control, a process that might end in the world becoming uninhabitable.” (Lean, Pearce, 2006) The Amazon rainforest has been characterised as the ‘lungs of the world.’ It is astonishing that though people know that without trees, they are without oxygen, the trees keep falling at increasingly larger rates. Trees are a resource that can be replenished if cutting is managed properly yet this has been anything but the case in the Amazon.

The collective rainforests of the world act as a climatic sponge storing much of the world’s rainwater, of which the Amazon rainforest accounts for more than half. Trees in the rainforest recycle water drawn from the forest ground. This, combined with the moisture that evaporates from the leaves is released into the atmosphere from whence it came. If not for this enormous amount of rainwater supplied by rainforests, rivers, lakes and land masses would essentially dry-up spawning droughts of epic proportions. Irrigation farming would be greatly curtailed. Disease, starvation and famine on a worldwide scale will be the direct result of deforestation. Trees cleanse the atmosphere by absorbing carbon dioxide and providing oxygen. Burning trees in the rainforest increases the amount of carbon in the atmosphere and at the same time reduces the amount of trees needed to absorb it. This contributes to global warming, a phenomenon which is already threatening the survival of the planet. (“Why” 2007).

The rising levels of carbon dioxide (CO2) in the atmosphere are becoming increasingly disconcerting. “The concentrations of CO2 in the air around 1860 before the effects of industrialization were felt, is assumed to have been about 290 parts per million (ppm). In the hundred years and more since then, the concentration has increased by about 10 percent.” (Breuer, 1980, p. 67). Eighty percent of the world’s population accounts for just 35 percent of CO2 emissions while the United States and Soviet Union combined are responsible for generating half. Worldwide, “carbon dioxide emissions are increasing by four percent a year.” (Miller, 1990, p. 450).

Motor vehicles are a major cause of air pollution as is fuel burned for the heating of homes and powering industry along with the toxins emitted from stacks at coal-burning power plants. “Vehicles produce high levels of carbon monoxides (CO) and a major source of hydrocarbons (HC) and nitrogen oxides (NOx), whereas, fuel combustion in stationary sources is the dominant source of sulfur dioxide (SO2)” (Breuer, 1980, p. 70).

If the balance between the CO2 levels in the ocean and atmosphere is disturbed by interjecting increasing amounts of CO2, the oceans would continually absorb higher concentrations than it does naturally. The subsequent warming ocean waters are less effective in their ability to absorb CO2 and when the oceans can no longer keep pace with the intrusion of this naturally equalized cycle, then more CO2 will remain in the atmosphere. Increasing the amount of CO2 in the atmosphere is expected to result in a warming of the Earth’s surface accelerating the greenhouse effect. “Currently carbon dioxide is responsible for 57 percent of the global warming trend. Nitrogen oxides contribute most of the atmospheric contaminants”.

The effects of air pollution are far-reaching and cannot be escaped by staying inside the home as indoor air pollution can be harmful, caused by such things as poor ventilation, mold and microbe-harboring air conditioning systems and ducts. The Environmental Protection Agency (EPA) reports that “toxic chemicals found in the air of almost every American home are three times more likely to cause some type of cancer than outdoor air pollutants” (Miller, 1990, p. 488).

The scientific community agrees that global temperatures are rising due to the burning of fossil fuels which are damaging the protective atmospheric Ozone layer by changing its composition. Human pollution is changing the climate of our earth and has increased global warming in the past half century. The effects are being felt worldwide, not just in the U.S. where most of the CO2 emissions are generated. In the UK., for example, four of the five warmest years for more than three centuries have occurred in the last 10 years. Scientists predict that in 50 years, annual temperatures in the south east of England could be at least three degrees (Fahrenheit) warmer, on average, than they are now (Climate Crisis 2000). Global warming is further evidenced by the well-documented melting of glaciers along with thermal expansion of the oceans, which have contributed to an increase in sea level over the past century of about six inches in that country. (Trenberth 1997).

Studies have been conducted by the National Aeronautics & Space Administration (NASA) have demonstrated that the past decade has been the warmest on record. At first thought, especially during the cold winter months, a little warming wouldn’t seem to be such a bad thing. Several varieties of fruits and vegetables could be produced in northern climates that today only grow in warmer climates. Warmer seas are likely to be attractive to more species of fish to the colder habitats as well. This is not to mention additional tourist currency to what would be the warm, sandy beaches of Canada or England (Climate Crisis 2000).

However, as in everything, there is a downside and in this case, one of horrific proportions. Studies in the UK have found that warming could increase rainfall by more than 20 percent during the winter by the 2080’s and decrease it by the same amount during summer months in the southern half of that country. This would cause severe droughts in some regions but areas such as East Anglia, a very low-lying region on the east coast of England, could very well be under water altogether.

One would have to wonder what enormous problems this will cause not only to people and property but to the health of the global economy as a whole. Entire sections of various countries will be forced to abandon their homes and businesses. The process will be a slow and torturous one. Scientists also worry about the effects of a changing climate on the Gulf Stream, a massive ocean current which acts to warm the continent of Europe. “Ocean currents transport large amounts of heat around the world: climatologists call it thermohaline circulation (THC)” (Climate Crisis 2000). If it slows down or moves further south as a result of Greenland melting, Europe could end up with a climate more like that of present-day Greenland. A BBC-produced television programme documented recently that Greenland is in fact melting at an alarming rate providing photographic evidence taken in the 1970’s in contrast to photographs taken in the present day.

This leads one to wonder if forces act to warm the climate yet at the same time cool it too, will these things balance each other to then have a neutral effect? Wishful thinking does no harm. Yes it does. That’s what much of the world leaders have done for thirty years. That’s how long we have known about the greenhouse effect, why it happened and what the results would be, but we have done little to avoid this calamity. Although science has identified a radically changing climate as the result of human activity, many will not admit it to themselves. “A parallel here is trying to link lung cancer to smoking.

There are always some people who smoke who do not get lung cancer, and some who get lung cancer who do not smoke. Yet the evidence is compelling that there is a link. Still there are always people who do not want to believe and justify their beliefs by feeding on the legitimate uncertainties that exist” (Trenberth 1997). This is, essentially, the same faction of those who think that change is inevitable, that our advancing technologies will enable us to adapt to climate change as it happens. In other words just ignore the problem by continuing to pollute for economic reasons and the problem will just go away. That doesn’t work for any other type of problem and won’t with this one either.

The question before us is, are we stewards of our earth and will we preserve it for future generations? If the past 30 years are any indication, then the answer is no. Noticeable effects of global warming are fairly insignificant right now to the average person, but its effects are unquestionably growing in scale. If the population of the planet were to immediately discontinue polluting the air with carbon dioxide emissions, climate changes would still continue long into the future. This is “because of the long lifetimes of carbon dioxide (centuries) and other greenhouse gases in the atmosphere and because of the thermal inertia of the oceans. The oceans overturn very slowly and take hundreds of years to adjust fully to changes, so that manifestations of changes that have already occurred are not yet fully seen” (Trenberth 1997).

The effects of melting snow caps and the resulting rise of sea levels have been well documented. Other effects are known but not as universally. A reduction of snow cover in addition to lake and sea ice will have dire consequences for locations at higher latitudes and lower elevations, especially in the winter and spring months. At increased temperatures, the atmospheric water vapor and resulting precipitation will be proportionately higher (Wunderlich & Kohler, 2001). Cloud compositions will change which will amplify the greenhouse effect. The increased levels of precipitation because of the warming at the polar regions will increase the effect. Shifting vegetation patterns, types and regional variations, will cause major human adaptations, the degree to which is open to speculation. The elevated evaporation rate will hasten the drying effect of soil subsequent to rainfall which will result in drier conditions in many regions.

Places that presently suffer through periodic drought conditions in the warmer months will be hardest hit. The more rapid water recycling rate will result in heavier rainfall amounts and the number of extreme rainfall events. Higher rainfall rates will cause increased tropical storm intensity in addition to the warmer temperatures. Hurricanes may be even more frequent and intense than presently predicted. As horrific as this near-future scenario is, it remains the land masses that will suffer the greatest changes as a result of the greenhouse effect. “Temperatures are expected to increase more rapidly over land compared to oceans because of the ocean’s higher heat capacity and because it can transfer more of the trapped heat to the atmosphere by evaporation. Over land, the warming has been and is expected to continue to be larger during nighttime than during daytime” (Wunderlich & Kohler, 2001).

In 1997 the Kyoto Treaty, which has now been signed by more than 160 countries, is, to date, the most comprehensive global effort to decrease CO2 emissions. Though the agreement was signed by the U.S. and then President Clinton consented to decrease greenhouse emissions in the U.S. by 40 percent, it has been dismissed by the Bush administration and has yet to be ratified by the U.S. CO2 greenhouse gases have since increased in the country that produces well more than any other. World leaders and environmentalists alike have proclaimed the treaty as a vital step on the road to abating the potentially cataclysmic global warming problem. Bush rejected the treaty because of economic concerns and his reservations regarding the scientific uncertainties of the greenhouse effect. (Melinin, 2005).


Most scientists worldwide accept the sufficient evidence that suggests global warming is already well underway and cannot be reversed anytime soon. They and reasonable people of all backgrounds and nationalities agree that if CO2 emissions are not greatly reduced and soon, the resulting greenhouse effect will alter the climate and possibly the sustainability of humankind. Unfortunately, the country that causes the most harm is lead by a person that seems to have ‘cause the most harm’ as his calling card.

Works Cited

Breuer, Georg. “Air in Danger: Ecological Perspectives of the Atmosphere.” New York: Cambridge University Press. (1980).

Climate Crisis: All Change in the UK?” BBC News. (2000). Web.

Lean, Geoffrey & Pearce, Fred. “Amazon rainforest could become a desert.” The Independent. (2006). Web.

Malinin, Sergei. “USA, China and India Outlaw Kyoto Protocol and Set Forth New Climate Change Initiative.” Pravda. (2005).

Miller, G. Tyler. “Living in the Environment: An Introduction to Environmental Science.” Belmont: Wadsworth. (1990).

Monson, Russell K.; Edwards, Gerald E.; Ku, Maurice S.B. “C3-C4 Intermediate Photosynthesis in Plants.” Bioscience. Vol. 34, N. 9, (1984), pp. 563-566 + 577-574.

Trenberth, Kevin E. “Global Warming: It’s Happening.” National Center for Atmospheric Research. (1997). 2008. Web.

“Why are the Rainforests Important?” Rain Forest Concern. (2007). Web.

Wunderlich, Gooloo S.; Kohler, Peter O. Improving the Quality of Long-Term Care. The National Academies Press. (2001). p.18.

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