The green house gas connection in the atmosphere has dramatically been increasing over the last 50 years. This has increased almost percent of the observed temperature. The largest contributing source of green house gases is the burning of fossil fuels like oil, gas, kerosene, etc. leading to the emission of carbon dioxide.
Global warming refers to a gradual increase in the average temperature of the earth at the lower atmosphere because of the increase in green house gases since in the industrial revolution. When sunlight reaches earth surface some is absorbed and warms in the earth. Most of the rest IR radiated back to the atmosphere at a longer wave length than the light. Water vapour, carbon dioxide(CO2),methane(CH4),ozone(O3),nitrous oxide, sulphur hexafluoride, hydro fluorocarbons, per fluorocarbons, chlorofluorocarbons, etc. in the atmosphere which act like a green house around the earth absorb some of this longer wavelengths before any escaped back in to space. The absorption of this long wave radiant energy warms the atmosphere. This green house gases act like a mirror and reflect back to the earth a part of the heat radiation, which would otherwise be lost to space. The more the concentration of the green house gases, the more heat energy is being reflected back to the earth or trapped inside the atmosphere. The reflecting back of heat energy by the atmosphere is called the green house effect.
It is reported that global warming raises the temperature of the earth by about 3 degree to 5 degree Celsius (5.4 degree to 9 degree Fahrenheit) by the year 2100. Further, the thermal expansion of the ocean due to global warming raises the sea levels by at least 25 meters (82 feet) by the year 2100.It is also reported that it causes increased cyclonic activity, changes in temperature and precipitation patterns, glacial retreat (They say that temperature raises on the Tibetan plateau, which are causing Himalayan glaciers to retreat.), etc. As global warming is most commonly connected with human interference, specially the release of excessive amounts of green house gases, steps to be taken deliberately to lower the green house gase.