Where do greenhouse gases come from?
Water vapour is the most important greenhouse gas, and occurs naturally in the atmosphere because of evaporation from the oceans and by a process known as transpiration in plants. We have very little or no control over the amount of water in the atmosphere. Carbon dioxide is the most important greenhouse gas which has man-made sources. Carbon dioxide is released by animals (including humans) when they breathe, by burning fossil fuels (coal, gas and oil) or wood, and through the cutting down of trees and plants which take in carbon dioxide. Methane is produced naturally when vegetation is burnt, digested or allowed to rot without oxygen being present. Methane also comes from rice fields, grazing cattle, landfill sites full of household rubbish, and coal mines. 90% of rubbish in the UK is disposed of in landfill sites, making up 29% of total man-made methane emissions in the UK. Nitrous oxide is produced naturally by the oceans.
