Global warming is caused by increased concentrations of greenhouse gases like carbon dioxide and methane in the atmosphere from human activities such as burning fossil fuels for electricity and transportation, deforestation, and agriculture. Burning coal and gas for electricity generation is Australia's main source of carbon pollution as 73% of its electricity comes from coal and 13% from gas. Deforestation and forest degradation account for up to one-fifth of global greenhouse gas emissions, while Australian farming contributes 16% of the country's total emissions.