During the last 100 years, humans have been burning oil, natural gas, peat and coal. In the next 50 years we will burn even more. Burning hydrocarbons produces carbon dioxide and water. How much has this water added to sea-level rise?
鈥� The cumulative amounts of oil and gas that have been used globally are not known with great precision but in the International Journal of Environmental Technology and Management (vol 7, p 99) suggest that up to the year 2000 we had burned 110 gigatonnes (Gt) of oil, 60 gigatonnes of oil equivalent (Gtoe) for natural gas and 150 Gtoe for coal. 鈥淥il equivalent鈥� refers to the amount of oil that contains the same primary energy as a given amount of natural gas or coal, based on standard conversion factors, although these factors can vary according to the source of the fuel, particularly for coal.
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By converting the oil equivalent tonnages to actual quantities of the individual fuels we arrive at 110 Gt of oil, 47 Gt of natural gas and 250 Gt of coal. Assuming all the hydrogen in each of the fuels is oxidised to water, one can estimate that oil will generate 140 Gt of water, natural gas 105 Gt, and coal 90 Gt.
Together that鈥檚 335 Gt of water, which has a volume of 335 cubic kilometres. The surface area of all Earth鈥檚 lakes and oceans adds up to about 360 million square kilometres. Spreading the water of combustion evenly over this area would result in rises of about 0.95 millimetres.
The journal also estimates that cumulative oil consumption would increase to 370 Gt for oil, 370 Gtoe for natural gas and 490 Gtoe for coal by the end of this century. This would lead to a total water level rise of about 4 millimetres.
David Williams, Watson, Australian Capital Territory