Global warming is the increase of the average temperature of the atmosphere, ocean and land Bumi.Temperatur global average on the Earth's surface has risen 12:18 ° C over the last century. Intergovernmental Panel on Climate Change (IPCC) concluded that, "most of the increase in global average temperatures since the mid-20th century, most likely caused by increased concentrations of greenhouse gases resulting from human activity through the greenhouse effect.
Rising global temperatures is expected to cause other changes such as rising sea levels, increased intensity of extreme weather events, as well as changes in the amount and pattern of precipitation. The effects of global warming include its impact on agricultural output, loss of glaciers and the extinction of various animal species. Most of the governments in the world have signed and ratified the Kyoto Protocol, aimed at reducing emissions of greenhouse gases.
Causes of global warming
1. The greenhouse effect
All energy sources that exist on Earth comes from the Sun. Most of the energy is in the form of short-wave radiation, including visible light. When the energy of the Earth's surface, he turned from the light into heat that warms the Earth. The surface of the Earth, will absorb some of the heat and reflect the rest. Some of this heat as long-wave infrared radiation into space. However, some of the heat remains trapped in the Earth's atmosphere due to accumulated amount of greenhouse gases include water vapor, carbon dioxide, and methane into the trap this radiation. These gases absorb and reflect radiation emitted heat the Earth, and consequently will be stored on the surface of the Earth. This happens repeatedly and resulted in an annual average temperature of the earth continues to rise. Gases may act as glass in a greenhouse. With the increasing concentration of these gases in the atmosphere, the more heat is trapped underneath. Actually, the greenhouse effect is very much needed by all living things on earth, because without it, the planet would be very cool. So ice will cover the entire surface of the Earth. However, due to the amount of these gases in the atmosphere has been excessive, a consequence of global warming.
2.Efek feedback
The effects of global warming-causing agents are also influenced by a variety of feedback processes that result. An example is the evaporation of water. In the case of warming due to increasing greenhouse gases such as CO2, warming will initially lead to more water to evaporate into the atmosphere. Because water vapor is itself a greenhouse gas, warming will continue and increase the amount of water vapor in the air until it reaches equilibrium with the water vapor concentration. The resulting greenhouse effect greater than the effect of CO2 alone. (Although this feedback increases the absolute water content in the air, the relative humidity of the air is almost constant or even decreases slightly because the air becomes warmer). This feedback can only be reversed slowly as CO2 has a long time in the atmosphere.
Feedback effects due to the influence of clouds is the subject of current research. When viewed from below, clouds will reflect infrared radiation back to the surface, thereby increasing the warming effect. In contrast when viewed from above, the clouds will reflect sunlight and infrared radiation to space, thereby enhancing the cooling effect. Whether the net effect of heating or cooling depending on some specific details such as the type and altitude of the cloud. These details are difficult to represent in climate models, partly because the cloud is very small compared to the distance between the boundaries of computational climate models (about 125 to 500 km for the models used in the IPCC Fourth report view
Another important feedback is the loss of reflectance (albedo) by es.Ketika global temperatures increase, ice near the poles melts at an increasing rate. Along with the melting of ice, land or water below will open. Both land and water has the ability to reflect light much less when compared to ice, and consequently will absorb more solar radiation. This will add to the heating and causing more ice to melt, causing a continuous cycle.
Positive feedback due to release of CO2 and CH4 from the softening of frozen ground (permafrost) are other mechanisms that contribute to warming. In addition, the melting ice will also release CH4 are also positive feedback.
The ability of the oceans to absorb carbon will also be reduced when it warms up, this is caused by the decreased levels of nutrients in the mesopelagic zone thus limiting the growth of phytoplankton are diatoms than a carbon sink that low.
3.Variasi Sun
There is a hypothesis that states that the variation of the Sun, with a possibility reinforced by feedback from clouds, can contribute in the current warming. The difference between this mechanism with the warming due to the greenhouse effect is the increased activity of the Sun would heat the stratosphere reverse the greenhouse effect should cool the stratosphere. Cooling of the lower stratosphere has been observed at least since 1960, that will not happen when solar activity being the main contributor to recent warming. (Depletion of the ozone layer can also provide the cooling effect but the depletion occurred from late 1970's.) Phenomenon solar variability combined with volcanic activity may have given the warming effect from pre-industrial to 1950, as well as a cooling effect since 1950 .
The impact of global warming
1.Pertanian
One might assume that a warmer Earth will produce more food than ever, but it is actually not the same in some places. Southern parts of Canada, for example, may benefit from the higher rainfall and growing season length. On the other hand, semi-arid tropical agriculture in some parts of Africa may not be able to grow. Agricultural areas that use irrigation water from distant mountains may suffer if the snowpack (snow collection) winter, which serves as a natural reservoir, would melt before the peak months of the growing season. Crop and forest insect attack and may experience a more severe disease.
4. Animals and plants
Animals and plants are living things that are difficult to avoid the effects of global warming because most of the land is controlled by humans. In global warming, animals tend to migrate toward the poles and up mountains. Plants will change the direction of growth, looking for new areas as old habitats become too warm. However, human development will deter this movement. Species that migrate north or south that are blocked by the cities or agricultural lands may be dead. Some types of species that are not able to quickly move toward the poles may also be destroyed.
5. Human health
In warmer world, scientists predict that more and more people are affected by the disease or die from heat stress. Outbreaks of diseases commonly found in the tropics, such as diseases caused by mosquitoes and other disease-carrying animals, will widen because they can move into areas that were previously too cold for them. Currently, 45 percent of the world's population live in areas where they can be bitten by a mosquito carrying the malaria parasite; percentage will increase to 60 percent if the temperature increases. Other tropical diseases such as malaria can also be spread, such as dengue fever, yellow fever, and encephalitis. The scientists also predict increased incidence of allergies and respiratory diseases due to warmer air will increase pollutants, mold spores and pollen.
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