The global consumption of fossil fuels is estimated to release 22 billion tonnes of carbon dioxide into the atmosphere every year and the amounts are still climbing. Methane is produced naturally when vegetation is burned, digested or rotted without the presence of oxygen. Large amounts of methane are released by garbage dumps, rice paddies and grazing cattle. Methane is significant because it has 21 times the heat-trapping effect of carbon dioxide. Nitrous oxide occurs naturally in the environment but human activities are increasing the quantities.
Nitrous oxide is released when chemical fertilizer is used in agriculture.
Since the beginning of the Industrial Revolution, concentrations of carbon dioxide have increased by 30 per cent, and methane by 145 per cent.