calcium carbonate cliffs of Dover and the petrol at motorway service
stations, both these substances represent large geological reservoirs
of carbon and, as such, long term carbon sinks.
Rates of formation of fossil organic carbon (fossil
fuel) are very slow, and dwarfed by the rate at which they are currently
being consumed by man. Current burning of fossil fuels by man is
releasing an estimated 5.3 thousand million tonnes of carbon back
into the atmosphere each year.
The formation of rock carbonates, such as the chalk
of Dover, is also very slow and is unlikely to match the use of
this carbon sink by man in cement production. At present, around
100 million tonnes of carbon is released to the atmosphere each
year from use of this geological carbon reservoir.
Some of the carbon, in such geological reservoirs
as chalk and fossil fuels, is released due to volcanic action. Global
emissions from this source can vary greatly from year to year depending
on levels of volcanic activity, but on average about 100 million
tonnes of carbon is reintroduced to the atmosphere each year via