Note: This Wikipedia article is a work in progress. Some terms may be misrepresented.

Climate forcing is the overall term for the various theories, sometimes called "climate forcing mechanisms" or "species of climate forcing," of the methods by which phenomena exert an effect on a climate. Forcing agents are the physical phenomena which "force," or effect changes on or influences the measure of a climate. Climate forcing can occur due to natural forcing agents such as a change in sunlight intensity (in terms of how much sunlight is being produced by the sun), or man-made agents such as pollution.

There are two main types of climate forcing. Climate forcing which results in a change in the amount of energy in the global climate is called radiative forcing. This type of forcing increases or decreases the total energy in the system by changing how much energy is reflected or retained. Climate forcing which influences or change climates significantly, but does not change the total amount of energy in Earth's climate, such as ocean circulation, is not considered a radiative type of forcing.

The pre-dominant methods of climate forcing on Earth are greenhouse gas forcing (radiative), also called the greenhouse effect, aerosol radiative forcing, and natural circulation within the climate. Climate models attempt to incorporate the methods of climate forcing and forcing agents into mathematical simulations of the global climate system.

Non-radiative forcing

Non-radiative forcing agents are natural physical phenomena which influence regional climate. They do not change the total energy within global climate system. Some of this type of forcing can be considered global rather than regional, as some of the respective forcing agents influence such a large number of climates. For instance, thermohaline circulation regulates climate across the world. Non-radiative forces can indirectly affect the total energy within the global climate by redistributing energy or substances in such a way that it affects a radiative forcing.

Examples of non-radiative forcing and their respective agents:

Ocean circulation

• Hydrothermal circulation
• Thermohaline circulation
• El Niño and La Niña

Atmospheric circulation

• Jetstream
• Westerlies

Orographic lift

This forcing occurs due to topographic/orographic forcing agents such as mountains.

Radiative forcing

Radiative forcing agents influence climate by changing the total amount of energy in the system. Energy is naturally added to the system via the Sun and is naturally lost from the system through heat radiation into space. Forcing agents which can change how much of this energy is added or lost are radiative climate forces. Additionally, stores of the Sun's energy, such as fossil fuels, can also add energy by releasing it into the system through physical processes such as combustion which releases potential chemical energy as heat. While it is technically correct to include fossil fuel combustion in the Earth's energy balance it is negligible as an atmospheric forcing when compared to solar forcing or greenhouse gas forcing [1]. The same is true of heating of the surface by conduction from the hot core of the planet. One must always take into account the magnitudes of various forcings. See radiative forcing for more details.

Examples of radiative forcing and their respective agents:

Greenhouse gas radiative forcing

The forcing agent is greenhouse gases.

Forcing mechanisms:

• Anthropogenic (human caused) gaseous air pollution
• Deforestation
• Carbon sinks
• Methane hydrate Clathrate compounds (see Paleocene-Eocene Thermal Maximum)
• Ozone depletion
• Volcanism†

Cloud radiative forcing

The forcing agent is clouds, and the mechanism is the natural circulation in the atmosphere.

Aerosol radiative forcing

Some of these forcing agents are:

• Airborne black carbon (soot)
• Other particulates in the air.

Forcing mechanisms:

• Anthropogenic (human caused) particulate air pollution
• Forest fires (which also release heat energy)
• Impact events
• Nuclear winters
• Volcanism†

Solar radiative forcing

The forcing agent is solar radiation from the sun.

Forcing mechanisms:

• Solar variations
• Milankovitch cycles (Orbital forcing)

Other radiative forcing

Heat

The forcing agent is anything that gives off heat.

Forcing Mechanisms:

• Urban heat island
• Forest fires

Albedo

The forcing agent is the Earth's landscape.

†Volcanic activity can release both aerosols and greenhouse gases.

See Also

• Greenhouse effect
• Climate model
• Climate change
• Global climate change
• Global warming potential
• Global warming
• Global cooling
• Global dimming

External Links

• Climate Forcing — Climate Monitoring and Diagnostics Laboratory
• Climate Forcing Data — National Geophysical Data Center