1. The greenhouse effect->When sunlight reaches Earth's surface some is absorbed and warms the earth and most of the rest is radiated back to the atmosphere at a longer wavelength than the sun light. Some of these longer wavelengths are absorbed by greenhouse gases in the atmosphere before they are lost to space. The absorption of this longwave radiant energy warms the atmosphere. These greenhouse gases act like a mirror and reflect back to the Earth some of the heat energy which would otherwise be lost to space. The reflecting back of heat energy by the atmosphere is called the "greenhouse effect".
2. Burning of Fossil Fuels such as oil,gas,petrol,Kerosene,etc.
3. The unwanted carbon dioxide from power plants,Cars,Airplanes and Buildings.
4. Deforestation.

The effects of Global Warming?

1. Say Goodbye to Ski Vacations
   Slopes on the East Coast last year closed months ahead of time due to warmer weather, some losing as much as a third of their season.
2. Say Goodbye to Salmon Dinners
   Get ready for a lot more chicken dinners: Wild pacific salmon have already vanished from 40 percent of their traditional habitats in the Northwest and the NRDC warns warmer temperatures are going to erase 41 percent of their habitat by 2090.
3. Say Hello to More Mosquitoes
   Get ready for more mosquitoes. Mosquitoes like to live in drains and sewer puddles. During long dry spells (brought on by higher temperatures) these nasty, stagnant pools become a vital source of water for thirsty birds ... which provide a tasty feast for the resident mosquitoes. At the same time, these dry spells “reduce the populations of dragonflies, lacewings, and frogs that eat the mosquitoes.”
4. More Floods
   During the summer of 2007, Britain suffered its worst flood in 60 years. Scientists point the finger directly at global warming, which changed precipitation patterns and is now causing more “intense rainstorms across parts of the northern hemisphere.