What do you mean by global warming? - QS Study
QS Study

Global Warming: Due to green house effect the earth is gradually being warmed up and the temperature is very slowly increasing. The reasons behind this green house effect are as follows:

From factories and industries every day large amount of carbon dioxide (CO2) is emitted in the atmosphere. This CO2 acts like the glass of a green house. The heat radiated of short wavelength can pass easily through this CO2, but long wavelength radiations cannot pass though it. Now radiations of short wavelength, produced by the sun fall on the earth’s surface which warm up the earth. But heat radiated by the earth has long wavelength since it radiates heat at lower temperature.

There waves are reflected back to earth. Consequently a very small increase of temperature of the earth takes place. This processes continuing and the global warming is taking place. As a result, the Ice in the poles is melting and water level of the oceans increasing. In future, a large portion of lower countries might go under water.