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 risen 0.74 ° C ± 0:18 (1:33 ± 0:32 ° F) 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"  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.
models referenced by the IPCC projects show global surface temperature
will rise 1.1 to 6.4 ° C (2.0 to 11.5 ° F) between 1990 and 2100. 
The difference in estimates was caused by the use of different
scenarios of greenhouse gas emissions greenhouse gases 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.
 This reflects the large heat capacity of the oceans.
global temperatures are expected to lead to other changes such as
rising sea levels, increased intensity of extreme weather phenomena,
 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.
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
CAUSES OF GLOBAL WARMING
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 ° C (59 ° F), the earth actually has more
hot 33 ° C (59 ° F) from the original temperature, if there is no
greenhouse effect the earth's temperature is only -18 ° C so that ice
will cover the entire Earth's surface. However, on the contrary, if these gases in the atmosphere have been excessive, will cause global warming.
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).  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. 
important feedback is the loss of ability to reflect light (albedo) of
ice.  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.
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.
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. (Riz@wikipedia.com)