What Warms and Cools the Earth?

There are three critical elements that affect the Earth's temperature change - greenhouse gases that warm the planet, human activities, and natural processes.  

Climate forcings (i.e., something that is imposed externally on the climate system by either human activities or natural processes) or climate feedbacks (i.e., an energy change that is produced within the climate system itself in response to a climate forcing).

Greeenhouse Gases Warm the Planet

The Greenhouse Effect

Carbon dioxide (CO₂) can be emitted naturally through the carbon cycle and through human activities. Since the Industrial Revolution in the 1700's, carbon dioxide concentration levels are increasing primarily due to the burning of oil, coal and gas, and deforestation.

Methane (CH₄) is a greenhouse gas that remains in the atmosphere for approximately 9-15 years. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO₂) over a 100-year period and is emitted from a variety of natural and human-influenced sources (e.g., raising livestock, growing rice, filling landfills, natural gas and petroleum systems, wastewater treatment).

Nitrous oxide (N₂O), commonly known as the laughing gas, is a colourless, non-flammable gas with a slightly sweet taste and odour. Agricultural activities and land use changes have contributed to the increasing concentration levels.

Ozone (O₃) forms naturally in the upper atmosphere, where it creates a protective shield that intercepts damaging ultraviolet radiation from the Sun. However, when ozone forms in the lower atmosphere, it becomes an air pollutant that has harmful effects on the respiratory systems of animals and will burn sensitive plants.

Halocarbons and chlorofluorocarbons (CFCs) are chemicals that have specialized uses in industries, such as refrigerants, fire retardants, adhesives, and pesticides. They have contributed to the damage of the ozone layer and as a result, most production of CFSs has been banned and concentrations levels are beginning to decline.

Human Activities Affect the Earth's Temperature

Most aerosols, such as sulfate (SO₄), cool the planet by reflecting sunlight back to space. Human activities, such as industrial processes, produce many different kinds of aerosols and the cooling of these aerosols produce one of the greatest remaining uncertainties in understanding present and future climate change.

Deforestation

Deforestation and other changes in land use modify the amount of sunlight reflected back to space from the Earth's surface. Changes in land use can lead to positive and negative climate forcing locally, but the net global effect is a slight cooling.

Black carbon particles or "soot,"is produced when fossil fuels or vegetation are burned, generally have a warming effect because they absorb incoming solar radiation.

Natural Processes Affect the Earth's Temperature

Volcanic Eruption

The Sun is Earth's main energy source. The Sun's output is nearly constant, but small changes over an extended period of time can lead to climate changes.

Volcanic eruptions emit many gases. One of the most important of these is sulfur dioxide (SO₂), which, once in the atmosphere, forms sulfate aerosol (SO₄). Large volcanic eruptions can cool the Earth slightly for several years, until the sulfate particles settle out of the atmosphere.