There are numerous causes that contribute to Climate Change
CO2 and Other Greenhouse Gas Variations
Many natural and human-made gases contribute to the greenhouse effect that warms the Earth’s surface. Water vapor (H2O) is the most important, followed by carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the chlorofluorocarbons (CFCs) used in air conditioners and many industrial processes. The increasing atmospheric CO2 concentration is likely the most significant cause of the current warming.
The world’s economy runs on carbon: the “fuel” in fossil fuels. Coal, oil, and natural gas contribute energy to nearly every human endeavour in industrialized nations, and carbon dioxide (CO2) is a by-product of burning these fuels. Immediately eliminating CO2 emissions would literally stop the industrial world. CO2 contributes more to the recent increase in greenhouse warming than any other gas. CO2persists in the atmosphere longer and longer as concentrations continue to rise.
Other chemicals such as methane, nitrous oxide, and halocarbons also contribute to the global greenhouse effect. A number of additional chemicals related to urban pollution, such as low-level (tropospheric) ozone and black soot, can have a strong regional and perhaps global warming effect. Sulfate aerosols may have a cooling effect.
There are contributors to gas emissions, including livestock farming, rice cultivation, gas flaring, and mining. Options for reducing methane emissions go beyond reducing beef and dairy consumption. Mitigation strategies also include reducing methane emissions from mines, gas production facilities, and landfills.
A volcanic eruption may send ash and sulphate gas high into the atmosphere, which may combine with water to produce tiny droplets (aerosols) of sulphuric acid, which reflect sunlight back into space. Large eruptions reach the middle stratosphere (19 miles or 30 kilometres high). At this altitude, the aerosols can spread around the world.
A massive volcanic eruption can cool the Earth for one or two years. The 1982 El Chichon eruption and the 1991 Pinatubo eruption caused the globally averaged surface temperature to cool less than 1°F.
Land Use Changes
When humans transform land from forests to seasonal crops or from natural to urban environments, the regional climate system is altered. For example, clear-cut hillsides are significantly warmer than forests. Urban environments are also islands of heat produced by industry, homes, automobiles, and by asphalt’s absorption of solar energy. Land use changes are not likely to have a large, direct effect on global average temperature.
Changing uses of the land are also associated with changes in the usage and availability of water, as well as the production of greenhouse gases. Deforestation can significantly increase the amount of atmospheric CO2, which warms the planet.
The atmospheric circulation (winds) and ocean currents carry heat from the tropics toward the poles. Many processes can alter these circulation patterns, changing the climate regionally or even over the whole world.
Interactions between the ocean and atmosphere can also produce phenomena such as El Niño, which tends to recur every two to six years. Changes in deep ocean circulation can produce longer-lived climate variations that endure for decades to centuries. The ice age cycles may have been influenced by changes in ocean circulation arising from changes in the Earth’s orbit around the Sun
The oceans play an important role in determining the atmospheric concentration of CO2. CO2 gas in the atmosphere and CO2 dissolved in the ocean surface reach a balance. Changes in ocean circulation, chemistry, and biology have shifted this balance in the past. Such changes may affect climate by slowly moving CO2 into or out of the atmosphere.
The Sun is the source of energy for the Earth’s climate system. Although the Sun’s energy output appears constant from an everyday point of view, small changes over an extended period of time can lead to climate changes.
Some scientists suspect that a portion of the warming in the first half of the 20th century was due to an increase in the output of solar energy. Learning how the Sun changed before modern instruments were available is not easy however, but it appears that changes in the output of solar energy have been small over the last million years, and probably even longer.
Slow changes in the Earth’s orbit lead to small but climatically important changes in the strength of the seasons over tens of thousands of years. Climate feedbacks amplify these small changes, thereby producing ice ages.
Earth’s orbit oscillates very slightly between nearly circular and more elongated every 100,000 years. This cycle is evident in the glacial/interglacial cycles of roughly the same period. The Earth’s orbital path varies in the degree to which it is circular. This change in its “eccentricity” varies between 0.00 and 0.06 on a 100,000 year cycle. When the eccentricity equals 0.00 the orbital path is circular and when it is 0.06 the orbital path is slightly elliptical.
The current value is 0.0167.
The Earth spins around an axis that is tilted from perpendicular to the plane in which the Earth orbits the Sun.
This tilt causes the seasons. At the height of the Northern Hemisphere winter the North Pole is tilted away from the Sun, while in the summer it is tilted toward the Sun. The angle of the tilt varies between 22° and 24.5° on a cycle of 41,000 years. When the tilt angle is high, the Polar Regions receive less solar radiation than normal in winter and more in summer. The Earth is tilted from perpendicular in its orientation to the Sun. This tilt varies from 22° to 24.5° on a 41,000 year cycle. The current tilt is 23.3°.
Wobble of the Earth’s Spin Axis
There is a slow wobble in the Earth’s spin axis, which causes the peak of winter to occur at different points along the Earth’s elliptical orbital path. This variation in the seasons occurs on an approximately 23,000-year cycle. The Earth’s axis of rotation wobbles like a top on a 23,000 year cycle. This causes the Earth’s seasons to reach their maximum at different distances from the Sun due to the elliptical shape of the Earth’s orbit.
Factors that can amplify or reduce the effect of the causes of change are known as “feedbacks.” These feedbacks consist of interconnected processes in which a change in one leads to a change in another, which ultimately leads to further changes in the first.
Small particles in the air (aerosols) may have warming or cooling effects, depending on their characteristics. Sulfate (SO4) aerosol, for example, is light-colored and reflects sunlight back into space. The cooling effect of volcanic aerosols from the Mt. Tambora eruption of 1815 caused North America’s “year without a summer” in 1816. Sulfate aerosol is also produced by fossil fuel burning.
Aerosol concentrations change for many reasons, including volcanic eruptions, spread of fires, increased windiness, drying of damp soils, changes in industrial processes, and more. Accurately projecting the extent and effect of aerosols is one of the major challenges in modeling the future of climate change.
Very small differences in clouds may produce large feedbacks. An increase in high, thin clouds produced by greenhouse warming would further increase the warming. This is because high, thin clouds are relatively effective in trapping infrared radiation (heat) while allowing the Sun’s energy to pass through. In contrast, an increase in thick, low clouds could lessen the warming because these clouds reflect sunlight efficiently. Changes in clouds result from changes in the distribution of water vapour, temperature, and winds. The effects of global warming on these factors are complex and not well understood.
Ice-free surfaces tend to absorb more solar energy than ice-covered surfaces. Therefore, snow and ice cover have a cooling effect on the Earth. If global warming reduces the global snow and ice cover, the warming will be enhanced because more solar energy will be absorbed. This ice-reflectivity feedback does not operate in Polar Regions during the winter, when it is always dark or the Sun is very low in the sky
Water vapour produces two-thirds of the world’s greenhouse effect. All of the other gases – carbon dioxide, methane, nitrous oxide, halocarbons, etc. – contribute the other third. The effect of water vapour is so significant that the global average temperature would be below freezing without it.
Warm air can contain more moisture than cold air. This is the basis of the water vapour feedback. As the atmospheric temperature rises and the amount of water vapour increases, the greenhouse effect is enhanced, further increasing temperature.
The water vapour feedback is critical for producing the glacial/interglacial cycles. Uncertainty in the magnitude of the water vapour feedback is an important source of uncertainty in projecting future climate warming.
Navigate to Climate Interactive and go to C-Roads Modelling (click here) where you can make a model for climate change based on different scenarios, including greenhouse gases, land use changes and more.