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Global Warming is the process of increasing the average temperature of the atmosphere, oceans and the Earth's land.

Global average temperature at Earth's surface has increased by 0.74 ТБ ТАC 0:18 (1:33 0:32 ТБ ТАF) during the last hundred years. 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 due to human activities" [1] via the greenhouse effect. These basic conclusions have been advanced by at least 30 scientific and academic bodies, including all the national science academies of the G8 nations. However, there are still some scientists who disagree with some conclusions that the IPCC noted.

Climate models referenced by the IPCC projects show global surface temperature will rise 1.1 to 6.4 ТАC (2.0 to 11.5 ТАF) between 1990 and 2100. [1] The difference in estimates was caused by the use of different scenarios of greenhouse-gas emissions glass in the future, as well as models of different climate sensitivities. Although most studies have focused on the period up to 2100, warming and lautdiperkirakan water level rise will continue for more than a thousand years even if greenhouse gas emission levels have been stable. [1] This reflects the large heat capacity of the oceans.

Increasing global temperatures are expected to lead to other changes such as rising sea levels, increased intensity of extreme weather phenomena, [2] and changes in the number and pattern of precipitation. Consequences of global warming is another character of agricultural output, loss of glaciers, and the extinction of various animal species.

Some of the things the scientists are still doubtful about the amount of warming predicted to occur in the future, and how warming and the changes that occur will vary from one region to another. Until now, there are still political and public debate in the world about what, if any, action should be taken to reduce or reverse further warming or to adapt to the consequences that exist. Most of the governments of the world's countries have signed and ratified the Kyoto Protocol, which leads to reduction of emissions of greenhouse gases.

Causes of global warming

Greenhouse effect

All energy sources that exist on Earth comes from the Sun. Most of the energy in the form of short-wave radiation, including visible light. When it reached the surface of the Earth's energy, he changed from light into heat that warms the Earth. The surface of the Earth, will absorb some heat and reflect back the rest. Some of this heat tangible long wave infrared radiation into space. However, some heat remains trapped in Earth's atmosphere due to accumulated amount of greenhouse gases include water vapor, carbon dioxide, and methane which trap the waves of this radiation. These gases absorb and reflect back the radiation waves emitted by the Earth and consequently the heat is stored in the Earth's surface. This situation occurs continuously resulting in annual average temperature of the earth continues to rise.

These gases function as a greenhouse gas. With the increasing concentration of these gases in the atmosphere, the more heat is trapped underneath.

The greenhouse effect is very much needed by all living things on earth, because without it, this planet will become very cold. With an average temperature of 15 ТАC (59 ТАF), the earth has actually been hotter ТАC 33 (59 ТАF) from the original temperature, if there is no greenhouse effect the earth's temperature is only -18 ТАC so the ice will cover the entire surface of the Earth. But on the contrary, if these gases in the atmosphere have been excessive, will cause global warming.
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Feedback effect

Elements of the cause of global warming is also influenced by various feedback processes that result. An example is the evaporation of water. In the case of warming due to increasing greenhouse gases like CO2, warming will initially lead to more number of water evaporates 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 the achievement of an equilibrium concentration of water vapor. The greenhouse effect it produces is larger than the effect of CO2 alone. (Although this feedback to improve the absolute water content in the air, relative humidity are almost constant or even slightly decreased because the air becomes warmer). [3] This feedback would have been only slowly as CO2 has a long age in the atmosphere.

Feedback effect due to the influence of clouds is becoming the object of current research. When viewed from below, clouds will reflect infrared radiation back to the surface, so that will increase the warming effect. In contrast when viewed from above, clouds will reflect sunlight and infrared radiation to space, thereby increasing the cooling effect. Does it produce a net effect of warming or cooling depending on some specific details such as the type and height of the cloud. The details are difficult to be represented 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 model used in the IPCC's view to the Fourth Report). Nevertheless, cloud feedback is at number two when compared with water vapor feedback and is considered a positive (adding heating) in all models used in the IPCC's view to the Fourth Report. [3]

Another important feedback is the loss of ability to reflect light (albedo) of ice. [4] As global temperatures increase, ice near the poles melts at a pace that continues to increase. Along with the melting of the ice, land or water below it will open. Both land and water has the ability to reflect light much less when compared with ice, and consequently will absorb more solar radiation. This would increase the warming and causing even more ice melts, becomes a continuous cycle.

Positive feedback due to release of CO2 and CH4 from the softening of frozen soil (permafrost) are other mechanisms that contribute to warming. In addition, ice that melts will also release CH 4 that also generate positive feedback.

The ability of oceans to absorb carbon will also be reduced if he warms up, this is caused by the decline in nutrient levels in the mesopelagic zone and limit the growth of diatoms than the phytoplankton which is a carbon sink that low. [5]
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Solar Variation

The variation of the Sun for 30 years.
The main article for this section are: Solar Variation

There is a hypothesis which states that the variation of the Sun, with a possibility reinforced by feedback from clouds, can contribute to current warming. [6] The difference between this mechanism with the warming due to greenhouse effect is the increased activity of the Sun would heat the stratosphere reverse the greenhouse effect will cool the stratosphere. Cooling the lower stratosphere has been observed since at least 1960, [7] are not going to happen when the solar activity becomes the major contributor to the current warming. (Depletion of the ozone layer can also provide the cooling effect but the depletion occurred from the late 1970s.) Phenomenon Solar variation combined with volcanoes probably had given the warming effect from pre-industrial times until 1950, and the cooling effect since 1950 . [8] [9]

There are some research results stating that the contribution of the Sun may have been overlooked in global warming. Two scientists from Duke University estimated that the Sun may have contributed to the 45-50% increase in average global temperature over the period 1900-2000, and about 25-35% between 1980 and 2000. [10] Stott and his colleagues argue that climate models currently used as guidelines to estimate exaggerated the effects of greenhouse gases compared to the influence of the Sun, they also suggest that the cooling effects of volcanic dust and sulfate aerosols have also been underestimated. [11] Nevertheless, they conclude that even with increased sensitivity the influence of climate on the Sun though, most of the warming that occurred in recent decades is caused by greenhouse gases.

In 2006, a team of scientists from the United States, Germany and Switzerland stated that they did not find an increase in the level of "explanation" of the Sun in a thousand years. Solar cycle to a small increase of 0.07% in brightness over the last 30 years. This effect is too small to contribute to global warming. [12] [13] A study by Lockwood and FrУЖhlich found that there was no relationship between global warming and variations of the Sun since 1985, either through the variation of solar output or variations in cosmic rays. [ 14]

Measuring global warming

Results of measurement of CO2 concentration at Mauna Loa

In early 1896, scientists thought that the burning of fossil fuels will change the composition of the atmosphere and to increase global average temperatures. This hypothesis was confirmed in 1957 when researchers working on global research program of the International Geophysical Year, took samples of the atmosphere from the top of Mauna Loa mountain in Hawaii.

The measurement results show an increase in the concentration of carbon dioxide in the atmosphere. After that, the composition of the atmosphere continues to be measured carefully. The data collected indicate that indeed an increase in the concentration of greenhouse gases in the atmosphere.

The scientists also have long suspected that the global climate warms up, but they are not able to provide appropriate evidence. Temperatures continue to vary from time to time and from one location to another location. Need many years of climate observations to obtain data that showed a tendency (trend) is clear. Note in the late 1980s showed a little of this warming trend, but statistics are few and can not be trusted.

Weather station at the beginning, is located close to urban areas so that the temperature measurement will be influenced by the heat emitted by buildings and vehicles and also heat stored by the building and road materials. Since 1957, the data obtained from a reliable weather station (located far from urban areas), and from satellites. These data provide a more accurate measurement, especially at 70 percent of the planet's surface covered with oceans. Data that more accurately shows that the surface of the Earth's warming trend actually occurs. When seen at the end of the 20th century, noted that the ten warmest years over the last hundred years occurred after 1980, and the three hottest years occurred after 1990, with 1998 being the hottest.

In a report issued in 2001, the Intergovernmental Panel on Climate Change (IPCC) concluded that global air temperatures have risen 0.6 degrees Celsius (1 degree Fahrenheit) since 1861. The panel agreed that the warming is mainly caused by human activities that add greenhouse gases to the atmosphere. The IPCC predicts an increase in global average temperatures will rise 1.1 to 6.4 ТАC (2.0 to 11.5 ТАF) between 1990 and 2100.

The IPCC panel also warned that although the concentration of gases in the atmosphere has not increased since 2100, still continues to warm climate during certain periods due to emissions that have been released previously. carbon dioxide will remain in the atmosphere for a hundred years or more before nature can absorb it again. [15]

If greenhouse gas emissions continue to increase, experts predict, karbondioksioda concentration in the atmosphere can be increased up to threefold in the early-22 th century when compared to the pre-industrial era. As a result, there will be dramatic climate change. Although the actual events of this climate change has occurred several times throughout the history of Earth, humans will face this problem with the risk of a very large population.
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Climate models