Global warming is caused by both natural phenomena and human activities that release greenhouse gases. Rising global temperatures melt glaciers and ice caps, causing sea levels to rise by approximately 1 inch every ten years. Some of the human factors that contribute to global warming include the burning of fossil fuels, industrial activities, automobile emissions, and aerosol sprays, which release carbon dioxide and other greenhouse gases into the atmosphere. If unchecked, global warming may lead to more severe weather events like hurricanes and tornadoes as well as rising sea levels that threaten coastal cities.