The average global temperature has increased by almost 0.5 centigrade degree over the past century; scientists expect it to rise by an extra 1~3 degree over the next 100 years.               Warmer weather makes glaciers melt, adding more water to the ocean. The warmer temperature also make water expand, so it takes up more space, causing the sea level to rise. The sea level has risen about 10~25 cm in the last 100 years.               The main cause of global warming is human pollution. Through burning coal, oil and gas, people have been increasing the greenhouse gases in the atmosphere, such as CO2. This adds to the power of the greenhouse effect, making the planet even warmer.               Many scientists believe that, if the warming is not stopped, there will be huge climate changes. The sea level could rise to one metre this century.               Should this come true, millions of homes will be swallowed up by the sea and the world will be flooded with "climate refugees" looking for somewhere to live? What's the basic reason that globe becomes warmer and warmer?
Coal, oil and gas. CO2. Human pollution. Greenhouse effect.