Methane (CH4) and Nitrous Oxide (N2O) are "greenhouse gases", meaning that they trap infrared radiation (heat) from the earth's surface and increase the temperature of the earth. Without this natural "greenhouse effect", temperatures would be about 33 degrees Celsius (60 degrees Fahrenheit) lower than they are now, and life as we know it today would not be possible. During the past century, humans have substantially added to the amount of greenhouse gases in the atmosphere through activities such as burning fossil fuels and deforestation. The added gases are enhancing the natural greenhouse effect, and very likely contributing to an increase in global average temperature and related climate changes. This book summarises the latest research and provides global estimates of current and future emissions of CH4 and N2O from natural sources, including emissions from newly identified sources.