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

The Earth's climate system is a compilation of the following components and their interactions-
The atmosphere
The hydrosphere, including the oceans and all other reservoirs of water in liquid form, which are the main source of moisture for precipitation and which exchange gases, such as CO2, and particles, such as salt, with the atmosphere.
The land masses, which affect the flow of atmosphere and oceans through their morphology (i.e. topography, vegetation cover and roughness), the hydrological cycle (i.e. their ability to store water) and their radiative properties as matter (solids, liquids, and gases) blown by the winds or ejected from earth's interior in volcanic eruptions.
The cryosphere, or the ice component of the climate system, whether on land or at the ocean's surface, that plays a special role in the Earth radiation balance and in determining the properties of the deep ocean.
The biota - all forms of life - that through respiration and other chemical interactions affects the composition and physical properties air and water.
The Earth has periods of time when the temperature rises (warming cycles) and periods when the temperature drops (cooling cycles) it is a series of natural cycles of our planet. The Sun and it's level of solar activity has an major influence on these cycles.

Today climate change and global warming are receiving unprecedented attention due to the possibility that human activity on Earth during the past couple hundred years will lead to significantly large and rapid changes in environmental conditions.

The first step in addressing the issue of global warming is to recognize that the warming pattern, if it continues, will probably not be uniform. The term "global warming" only tells part of the story; our attention should be focuses on "global climate change." The real threat may not be the gradual rise in global temperature and sea level, but the redistribution of heat over the Earth's surface. Some spots will warm, while others will cool; these changes, and the accompanying shifts in rainfall patterns, could relocate agricultural regions across the planet.