Global warming refers to the rise in surface temperature of the Earth caused by increased levels of greenhouse gases like carbon dioxide in the atmosphere from human activities. It is a major environmental issue as it is believed to be permanently changing the Earth's climate by melting glaciers and raising sea levels, which can cause flooding in low-lying areas. The primary cause of global warming is the emission of greenhouse gases through human activities like the combustion of fossil fuels for transportation, manufacturing, and power generation.