Global warming is caused by greenhouse gases like carbon dioxide and methane that trap heat in the atmosphere. This has led to increased global temperatures and melting of polar ice caps. Effects of global warming include rising sea levels that threaten coastal areas, changed animal migration and breeding patterns, and more frequent extreme weather. While some argue past climate changes were also natural, most scientists agree the current rapid warming is mostly human-caused by greenhouse gas emissions from things like fossil fuel combustion and deforestation. Preventing further global warming requires reducing these emissions through alternatives like renewable energy and tree planting.