The earth has an average temperature of 33 degree celcius 33°C which makes life possible on earth. This is due to:
Carbon dioxide and methane in the earth's atmosphere behave as a huge greenhouse and keep the earth warm enough to support the large diversity dwelling on it. But, due to activities like burning of fossil fuels the concentration of these greenhouse gases increases in the environment. This leads to enhanced greenhouse effect which ultimately causes global warming that leads to melting of polar ice caps, sudden increase in temperature, etc.