Greenhouse Effect

Greenhouse Effect & Enhanced

Greenhouse Effect

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Ð'* Introduction

Ð'* Greenhouse Gases & Enhanced Greenhouse Effect

Ð'* Climate Feedbacks on an Enhanced Greenhouse Effect

Ð'* Methodology for Enhanced Greenhouse Effect Measurement & Data

Ð'* Summary

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Introduction

Ð'* Greenhouse Effect

Ð'* A Simplied Radiative Equilibrium Model

Ð'* Variability of Global Temperature -- Global Warming?

Ð'* Natural Climate Variability vs. Enhanced Greenhouse Effect

Ð'* Potential Effects of Global Warming

Ð'* Greenhouse Myths

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Greenhouse Effect

The greenhouse effect results from "the dirty of the atmospheric infrared window" by some atmospheric trace gases, permitting incoming solar radiation to reach th surface of the Earth unhindered but restricting the outward flow of infrared radiation. These atmospheric trace gases are referred as greenhouse gases. They absorb and reradiate this outgoing radiation, effectively storing some of the heat in the atmosphere, thus producing a net warming of the surface. The process is called the greenhouse effect.

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A Simplied Radiative Equilibrium Model

The greenhouse effect plays a crucial role in maintaining a life-sustaining environment on the earth. If there is no greenhouse effect (suppose that there is no greenhouse gases existing in our atmosphere), the temperature of the earth is determined by the amount of incoming solar radiation that reaches and heats its surface. The amount of incoming solar radiation received at the Earth's surface is given by pi*R^2*S*(1-A), where R is the radius of the earth; S is the solar constant; and A is the albedo of the earth. (The albedo of the earth is approximately 33%.) This amount of incoming solar radiation reaches the surface of the earth and heats it to a temperature, called the effective temperture, Te. Supposing that the earth emits heat like a blackbody, each square meter of the earth's surface radiates infrared radiation according to the stefan-Boltzmann law, which states that the emission of infrared radiation is equal to o*Te^4, where o is the the Stefan-Boltzmann constant. Hence, the total amount of infrared radiation emitted by the earth's surface is equal to 4*pi*R^2*o*Te^4. Since there is a balance between the incoming solar radiation reaching the surface and the outgoing infrared radiation emitted at the surface, we may equate these two terms and solve for the effective temperture, Te. It is easy to find that Te=(S*(1-A)/4o)^(1/4) and to get the earth Te=253K.

At a temperature of 253K, the earth would be a very inhospitable, frozen world. However, actual measurements indicate that the mean temperature of our planet averaged over the year and over all latitudes is about 288K, rather than 253K. This difference is due to the greenhouse effect.

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Variability of Global Temperature -- Global Warming?

The various independent historical observational measurements conclude that the global average near-surface temperature has increased by about 0.5 degree centigrade over the past 100 years. This observed warming trend is continuing despite the influence of the Mt. Pinatubo volcanic eruption, which caused volcanic emissions to reduce incoming solar radiation for nearly two years. The likelihood that this global warming is due to primarily to natural variability is low. Scientists believe that this global warming trend is resulted from the enhanced greenhouse effect. The notion of an "enhanced" greenhouse effect refers primarily to the incremental global warming caused by the exponentially increasing concentrations of anthropogenically introduced greenhouse gases over and above the greenhouse effect caused by naturally occuring greenhouse gases. Although there exist large uncertainties, scientists suggest that the emissions of greenhouse gases and sulfate aerosols could, by the end of the next century, lead to an increase in global mean temperatures of about 1-4 degree centigrate.

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Potential Effects of Global Warming

This global warming trend can cause a significant global climate changes. Human society is highly dependent on the Earth's climate. Climate patterns and human adaptations determine the availability of food, fresh water, and other resources for sustaining life. The social and economic characteriatics of society have also been shaped largely by adapting to the seasonal and year-to-year patterns of temperture and rainfall. Some potential effects associated with climate change are listed in the following. (from U.S. Climate Action Report)

Ð'* Water Resources

The quality and quantity of drinking water, water availability for irrigation, industrial use, and electricity generation, and the health of fisheries may be significantly affected by changes in precipitation and increased evaporation. Increased rainfall may cause more frequent flooding. Climate change would likely add stress to major river basins worldwide.

Ð'* Coastal Resources

A estimated 50 cm rise in sea level by the year 2100, could inundate more than 5,000 square miles of dry land and an additional 4000 square miles of wetlands in the U.S.

Ð'* Health

Heat-stress mortality could increase due to higher temperatures over longer periods. Changing patterns of precipitation and temperature may produce new breeding sites for pests, shifting the range of infectious diseases.

Ð'* Agriculture

Impacts of Climate change in developing countries could be significant.

Ð'* Forests

Higher