Man-made emissions of carbon dioxide have upset the Earth’s natural balance; natural sinks can no longer extract this extra greenhouse gas from the atmosphere so we have global warming. More ….
 
Carbon dioxide is emitted by a variety of sources and absorbed by a variety of sinks that make up a natural carbon cycle. Carbon dioxide is emitted by the respiration (‘breathing’) of plants, fungi, animals and some bacteria. These natural carbon dioxide emissions amount to around 770 billion tonnes of carbon dioxideper year. Carbon dioxide is absorbed by photosynthesising plants on land and in the sea and directly by dissolving in the oceans. The natural exchanges have been kept in balance for many thousands of years by the above processes. For the last 500,000 years the concentration of carbon dioxide in the atmosphere has remained relatively steady between 180 and 300 parts per million.
 

However, since pre-industrial times (around 1750) mankind has emitted large quantities of carbon dioxide into the atmosphere by burning fossil fuels (coal, oil and gas). Since 2000 this has amounted to around 26 billion tonnes of carbon dioxide every year, i.e. only about 3% of the emissions produced naturally. Even so, this relatively small amount and the continuing relentless increase in the amount of carbon dioxideremaining in the atmosphere, almost 40% since 1750, means that the natural equilibrium of the Earth’s system has been upset. The sinks can no longer cope with the amounts of carbon dioxide being added to the atmosphere and global warming is the result.