Global warming refers to the rising average temperature of the Earth caused by greenhouse gas emissions from human activities like burning fossil fuels. The greenhouse effect occurs naturally but is enhanced by increasing concentrations of greenhouse gases, trapping more heat in the lower atmosphere and leading to global warming. The major greenhouse gases are carbon dioxide, methane, and nitrous oxide, which have all increased due to human activities and contribute to rising global temperatures and sea levels as well as changes to weather patterns and water supplies. Reducing energy usage and switching to renewable energy can help limit the effects of climate change.