Global Warming P#1

Global Warming

The term Global Warming refers to the observation that the atmosphere near the Earth's surface is warming. This warming is one of many kinds of climate change that the Earth has gone through in the past and will continue to go through in the future. It is reasonable to expect that the Earth should warm as the amount of greenhouse gases in the atmosphere increases. It is known for certain that atmospheric concentrations of greenhouse gases are rising dramatically due to human activity. It is less well known exactly how the increases in these greenhouse gases factor in the observed changes of the Earth's climate and global temperatures.

Energy from the Sun reaching the Earth drives almost every known physical and biological cycle in the Earth system. The energy that keeps the earth's surface warm originates from the sun. The primary source of energy to drive our global climate system (including atmospheric and, to a lesser extent, oceanic circulation) is the heat we receive from the Sun, termed solar insolation. The amount of insolation which reaches the Earth's surface depends on site latitude and season. The insolation into a surface is largest when the surface directly faces the Sun. As the angle increases between the direction normal to the surface and the direction of the rays of sunlight, the insolation is reduced in proportion to the cosine of the angle. This is known in optics as Lambert's cosine law.

These false-color images show the average solar insolation, or rate of incoming sunlight at the Earth's surface, over the entire globe for the months of January and April. The colors correspond to values (kilowatt hours per square meter per day) measured every day by a variety of Earth-observing satellites and integrated by the International Satellite Cloud Climatology Project (ISCCP). NASA's Surface Meteorology and Solar Energy (SSE) Project compiled these data--collected from July 1983 to June 1993--into a 10-year average for that period. Credit Image courtesy Roberta DiPasquale, Surface Meteorology and Solar Energy Project, NASA Langley Research Center, and the ISCCP Project

This 'projection effect' is the main reason why the polar regions are much colder than equatorial regions on Earth. On an annual average the poles receive less insolation than does the equator, because at the poles the Earth's surface is angled away from the Sun.

Although the energy that is emitted from the sun is almost constant, even small changes can have noticeable effects. When the Sun's energy reaches the Earth it is partially absorbed in different parts of the climate system. The absorbed energy is converted back to heat, which causes the Earth to warm up

There are three main factors that directly influence the energy balance of the earth and it's temperature:
The total energy influx, which depends on the earth's distance from the sun and on solar activity
The chemical composition of the atmosphere
Albedo, the ability of the earth's surface to reflect light.

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