What is the phenomenon of the gradual increase in average temperature of Earth's atmosphere is known as?

Global Warming

The correct answer is option (2) - Global Warming

The burning of fossil fuels, emissions from automobiles and chlorofluorocarbon add to the greenhouse gases in the atmosphere. This has led to an increase in the earth's temperature causing environmental changes. This increase in temperature across the globe is known as global warming.

The Kyoto Protocol is an international agreement setting targets for industrialised countries to cut their greenhouse gas emissions. Certain gases like Carbon dioxide, Methane, Hydro- fluoro carbons etc. are considered at least partly responsible for global warming - the rise in global temperature which may have catastrophic consequences for life on Earth. The protocol was agreed to in 1997 in Kyoto in Japan, based on principles set out in UNFCCC.