Global warming is an increase in the average temperature of the Earth's atmosphere and oceans. Most of the observed temperature rise since the 1950s has been caused by increasing greenhouse gas emissions. If global warming increases temperatures by over 2 degrees Celsius, the United Nations report predicts water shortages will start, sea levels will rise, and food stocks around the world may run out, leading to migration issues. Solutions proposed to address global warming include using energy-efficient light bulbs, reducing car usage, contributing to recycling programs, using less hot water, planting trees, and preventing burning in forests.