Global warming is one of the most important issues facing the world today. As we move into the 21st century, it is crucial to understand Global Warming in the 21st Century Its effects and future. This will help explain these aspects. Global warming is the gradual increase in the Earth?s average surface temperature. This warming is caused by human activities that release gases into the atmosphere. These gases trap heat from the sun, similar to how a greenhouse works. To understand the full global warming read Global Warming in the 21st Century Causes Effects and Future book or Global Warming Myth or Reality book.