Climate variation factors

The climate of any region is largely determined by four geographic aspects:

Latitude, distance from the sea, direction of the prevailing winds and elevation.

Climate variation factors

Other factors influence the global climate system: atmosphere, oceans, ice, land and the various forms of life.

Ultraviolet, visible and infra-red solar radiations are Earth's main sources of energy. There is an established balance between the incmoing solar energy and the telluric infra-red radiation emitted by the Earth. Part of the Earth's radiation is absorbed and reemitted by the 'greenhouse' effect and part is lost in space. You'd be hard pressed to find people anywhere that don't have an opinion on the 'greenhouse' effect or solar radiations one way or the other.

Horizontal variation of solar energy

The balance is fragile and any variation in the factors that affect this incoming and outgoing energy process or which modifies the energy repartition will affect the world climate.

Natural factors

The climate changed during Earth's history. Ice ages alternating with warm periods provide an example. Some changes were worlwide, while others simply affected an area or a hemisphere. In addition, a number of natural factors contribute to modify the Earth's climate during various periods. It is important to understand these factors when seeking to detect the influence of humanity on the climate:

  • Variations of the solar energy emissions. The quantity of energy emitted by the Sun is not constant. There are evidences revealing that the Earth's temperature corresponds to a solar cycle. Long term changes can occur.

  • Modifications of the Earth's orbit. The orbit of the Earth around the Sun changes slowly. This influences the quantity of energy which is reflected and absorbed. It is thought that these variations of Earth's orbit are one of the factors that triggered the ice ages.

    Seasonal variations of the air temperature

  • The greenhouse effect. Approximately 1/3 of the energy emitted by the Sun returns to space after penetrating Earth's atmosphere. A fraction of what remains is then absorbed by the atmosphere, but the major part is absorbed by the Earth's surface. The surface returns infra-red energy and while part of this energy is lost in space, another part is absorbed again and re-emitted by the clouds and gases like water vapor, carbon dioxide, methane and oxide nitrous. This contributes to heat Earth's surface and the troposphere to a temperature 33C higher than what it would be otherwise.It is the natural greenhouse effect which is essential for life.

  • Aerosols. These are very fine particles that remain in suspension in the atmosphere during a very long time. They reflect the solar radiation and also absorb it. By modifying the quantity of the aerosols in the atmosphere, one modifies the quantity of the reflected and absorbed solar energy.

    Human factors

  • The greenhouse effect amplification. The greenhouse gases naturally present in the atmosphere (e.g., water vapor, carbon dioxide, methane and oxide nitrous) keep the Earth at a sufficiently high temperature so that life is possible. Scientific studies reveal that various human activities, whose combustion of fossile fuels for producing electrical energy, heating and transport, produce greenhouse gases. By increasing concentrations of these gases and by rejecting new greehouse gases such as chloroflurocarbures (CFC), humans are likely to be contributing to increasing the average temperatures of Earth.

  • Lan use evolution. By replacing forests with arable lands or the natural vegetation by asphalt and concrete, humanity modifies the way in which terrestrial surface reflects sunlight and releases heat. All these changes can also modify the regional configurations of evaporation, streaming and rains.

  • Atmospheric aerosols. Due to its agricultural and industrial activities, humanity adds great quantities of fine particles called aerosols to the atmosphere. Most of the aerosols are quickly falling due to gravity and precipitations, but they do not less influence the atmosphere radiative absorption. It is the quantity and the nature of these particles as well as the nature of underneeth surface (land or water) that determine if this have a heating effect of not. Nevertheless, the regional effects can be important.