What is Global Warming? – Definition, Causes and Effects

Advances in technology have expanded the scope of Biology Topics we can investigate and understand.

The Greenhouse Gases Causing Global Warming

A building mostly made of glass for growing or sheltering delicate plants is called a greenhouse. The glass walls of the greenhouse allow sun rays to pass through to the interior. However, reflected back infrared rays are not allowed to escape through the glass walls. Carbon dioxide gas and water vapours present inside the glasshouse further trap the heat and make the greenhouse warmer than the outside air.

The atmosphere covers’ the Earth and acts similar to the glass walls of a greenhouse. The air cover allows solar radiation to pass through it to the Earth’s surface but prevents the long-wave infrared radiation (which is reflected back from Earth) to escape into space. Gases such as carbon dioxide (CO₂), methane (CH₄), ozone (O₃), nitrogen oxide (N₂O), and chlorofluorocarbons (CFCs) are called greenhouse gases (GHGS). Among them, CO₂ is the most important greenhouse gas.

Burning of fossil fuels in homes, industries, automobiles, burning associated with agricultural practices, deforestation, etc., all such practices are increasing levels of CO₂ and CH₄ in the atmosphere. These greenhouse gases (mainly carbon dioxide and methane) trap the heat (infrared radiation) reflected by the Earth. This heating up of the atmosphere leads to an increase in Earth’s temperature. This phenomenon is called global warming or the greenhouse effect. These gases are radiatively active, i.e., they allow the solar radiations to pass through them but reflect back the long wave radiations.

Effect of Global Warming

An increase of as less as 1°C in Earth’s temperature can lead to the melting of polar ice caps and consequent rise in sea level. A rise in sea level can submerge a number of major cities of the world, which are located along the sea coasts. Besides causing floods in low-lying coastal cities, global warming poses a threat of recurrence of the dust bowl condition of the 1930s. A dust bowl is an area where vegetation has been lost and soil reduced to dust making it susceptible to erosion.

The increased global temperature might change fertile croplands into deserts. In 1930, a dust bowl occurred in the USA, when prolonged drought, planting, and agricultural mismanagement allowed soil layers to dry out and topsoil to blow away driving people from their land. The dust bowl conditions of the 1930s could befall the great grain-producing regions of the American Midwest, Canada, and the Soviet Union. Irrigation would probably not correct the situation, because groundwater reserves would quickly become depleted.

An increase in the temperature of the Earth due to the greenhouse effect will cause a change in weather and precipitation patterns on the Earth.

One of the dangers of continued global warming is “methane burp” which is caused by the melting of the methane hydrates in permafrost (of polar ice) and on the sea floor. Methane is a greenhouse gas that increases global warming.

Biological Control of the Geochemical Environment

Air is a mixture of many gases such as nitrogen, oxygen, carbon dioxide, and water vapour. It is interesting to note that even the composition of air is the result of life on Earth. This is called the Gaia hypothesis. In planets such as Venus and Mars, where no life is known to exist the major component of the atmosphere is found to be carbon dioxide.

Gaia Hypothesis
Gaia’s hypothesis holds that organisms, especially microorganisms, have evolved with the physical environment to provide an intricate self-regulatory control system that keeps conditions favourable for life on Earth (Lovelock 1979).

The atmosphere of Venus traps heat and creates a maximum surface temperature of 48°C, making Venus the hottest planet in our solar system. In contrast, Mars is a cold planet. The highest temperature of Mars is 10°C and the lowest is 100°C. It has polar caps of frozen CO2 and ice.

Comparison of the major components of the atmosphere on the planet Earth, Mars, and Venus. The percentage represents a number of molecules (moles), not relative weights. Elements without percentage values are present in trace amounts.