Because global warming is the result of increase in the earth's average surface temperature due to greenhouse gases like carbon dioxide and methane. These gases are required for the presence of human on earth. Global warming is causing the colder areas of the world to become more hot, thereby becoming more vulnerable to diseases. Then effect of global warming is causing droughts, hurricanes, wildfire, extinction on endangered species, melting of polar ice and storm. However, changes resulting from global warming may include rising sea levels due to melting of the polar ice caps, as well as increase in occurence and severity of storms and other severe weather events.