Global Warming

An important definition first.

Equilibrium =

A condition in which all acting influences are cancelled by others resulting in a stable, balanced, or unchaging system.

As an example consider the human population. It increases due to births, and decreases due to deaths. In a period if births and deaths occur in equal numbers, the population will remain in equilibrium. So far, we have always seen more human births than deaths, that's why human population has never been in an equilibrium, it has always been growing. For another example let us consider the level of water in a lake. When water inflow occurs due to rain or other sources, the level rises. When water outflow occurs due to evaporation or other reasons, the level goes down. When the inflows and outflows occur in equal amounts, the lake's water level will reach an equilibrium. Let us now come to the main topic of this section. By absorbing the energy from sunlight in daytime the earth warms up. It sends some of this energy back into outerspace through infrared radiation. The earth's temperature will remain in equilibrium if the amount of energy absorbed from incident sunlight, and that sent back into outerspace through infrared radiation are equal. Until recently earth's temperature has been at an equilibrium for a long time. Some gases in the air, called green house gases have the property of preventing the dissipation of energy into outer space by absorbing the infrared radiation going out, and sending some of it back towards the earth, adding to its warming. Water vapor is a green house gas. Since a cloud is a visible body of water vapor, we feel nice and cozy on cloudy nights in winter. On the other hand on a clear cloudless night in winter we feel the shiver-inducing cold. Carbon dioxide $(CO_2)$ is a more effective green house gas than water vapor, it absorbs more of the outgoing infrared radiation than water vapor. Until the 18th century, the percentage of $CO_2$ in the air by volume used to be 0.027. Fuel is any material that provides useful energy. Natural fuels like coal. petroleum (also called crude oil), and natural gas obtained from underground deposits that were formed millions of years ago from the remains of ancient plants and animals are called fossil fuels. Fossil fuels release energy when they are burnt with oxygen in the air, this also releases large quantities of green house gases (mainly $CO_2$, and nitric and nitrous oxides generally referred to as $NO_x$) into the air. All our technologies require large amounts of energy as input. We are obtaining a small portion of this energy from nuclear reactors and hydroelectric power plants. But almost 97% of the energy that people use today is produced by burning fossil fuels. This releases large quantities of $CO_2$ and other green house gases into the air, making up the most important air pollution being created by human activities. Vegetation and trees absorb $CO_2$ from the air and in the process of photosynthesis they synthesize carbohydrates from $CO_2$, water, and energy from sunlight; with the simultaneous release of oxygen. However, the amount of $CO_2$ that we are releasing into the air by burning fossil fuels far exceeds the amount of $CO_2$ absorbed from the air in photosynthesis by plants. Because of this, the equilibrium of $CO_2$ in the atmosphere is upset, and its percentage in the air is increasing. Now it has reached 0.037 by volume, and continues to increase. Since $CO_2$ is a very effective green house gas, this has upset the temperature equilibrium, and the earth's climate is getting warmer. This phenomenon is called global warming or green house warming. The main reason for this global warming has been shown to be the large quantities of green house gases being released into the air by the burning of fossil fuels by mankind. There have been numerous reports in scientific journals and newsmedia documenting evidence of global warming. We will cite a couple of these. In $[2]$ it has been reported that in August 2000, for the first time in 50 million years, the north pole is awash in water because the thick ice that has for ages covered the Arctic Ocean at the pole has turned to water. The report says that an ice-free patch of ocean about a mile wide has opened at the top of the world, this same area was observed six years ago to have been covered by a layer of ice at least nine feet thick. This report and $[4]$ conclude that the rate of atmospheric and oceanic warming has accelerated significantly in the last quarter century. In $[3]$ it is reported that ocean temperatures in the tropical northern hemisphere are going upwards by 10 times the global average, due to which there is a very high probability that coral reefs as we know them now will be gone in 30 to 50 years. Other effects of our activities are discussed in the following sections.