The earth must maintain balance between the outgoing radiation and the incoming solar energy always. If there is any change in the factors that affect this process of incoming and outgoing energy, or change the energy distribution itself the earth’s climate will change and effect many aspects of the environment. There are different factors, both natural and human, that threaten this fragile balance.
· Changes in Solar Output: the amount of energy radiating from the earth’s sun is not constant.
· Changes in the Earth’s Orbit: Slow variations in the Earth’s orbit around the sun change where and when energy is received on earth. This affects the amount of energy that is reflected and absorbed.
· The Greenhouse Effect: When energy from the sun enters the Earth’s atmosphere, about a third of it is reflected back to space. Of the rest, the atmosphere absorbs some, but most of it is absorbed by the surfaces of the earth. The Earth emits energy at longer wavelength. Some of this energy escapes to space but some is absorbed again and remitted by clouds and the greenhouse gases such as water vapor, carbon dioxides, methane and nitrous oxide. This helps to warm the surface and the troposphere (lowest layer of the atmosphere), keeping it 33°C warmer than it would be otherwise be.
· Aerosols: these are fine particles and droplets that are small enough to remain suspended in the atmosphere for considerable periods of time. They both reflect and absorb incoming solar radiation. Changing the type and quantity of aerosols in the atmosphere affects the amount of solar energy reflected or absorbed.
- Enhancing the Greenhouse Effect: naturally occurring greenhouse gases, as described above, keep the Earth warm enough to support life. However, scientific studies have shown that a variety of human activities release greenhouse gases. These include the burning of fossil fuels for producing electrical energy, heating and transportation. By increasing their concentrations and by adding new greenhouse gases like CFCs, humankind is capable of raising the average global temperature.
· Land Use Change: As humans replace forests with agricultural lands, or natural vegetation with asphalt or concrete, they substantially alter the way the Earth’s surface reflects sunlight and releases heat. All these changes also affect regional evaporation, runoff and rainfall patterns. Land use and the changes in the way it is used effect the global carbon cycle, reduce the world’s forests and woodlands, expand the cropped land area, and cause tropical deforestation. As well, there is increased productivity of labor in exploiting land through the application of capital and new technologies. Conversion of land from natural to agricultural use also upsets the balance.
· Atmospheric aerosols: Humans are adding large quantities of fine particles (aerosols) to the atmosphere, both from agriculture and industrial activities. Although most of these aerosols are soon removed by gravity and rainfall, they still affect the radiation balance in the atmosphere. Whether this effect adds to or offsets any warming trend depends on the quantity and nature of the particles as well as the nature of the land or ocean surface below. The regional effects, however, can be significant.
· Burning of Fossil Fuels for Energy: As humanity burns the organic matter from past geologic periods (or the forests of today) to power the engines and economies of modern society, we are re-injecting our fossil carbon legacy into the atmosphere at incredibly accelerated rate. Carbon dioxide is dumped into the atmosphere at a much faster rate than it can be withdrawn or absorbed by the oceans or living things in the biosphere. The carbon dioxide buildup is a principal controlling factor of the climate change.