6. Water released from fossil hydrocarbons
In the previous section, the discussion assumed constant volume of water dispatched between ice caps, floating ice and land ice since matter cannot escape to space. However the combustion of all the hydrocarbons (oil, natural gas, and biomass) generates hot CO2 from the carbon content and hot water vapor from hydrogen. Once the heat stored in these hot gases is transferred to the environment; the generated cool water becomes surplus of water on Earth.
Quantifying the amount of such extra water is as difficult as quantifying e and rAHRs. Nevertheless, data on the overall production of fossil oil and natural gas are available and provide means to estimate the surplus of water. Between 1870 and 2018, about 180 Gt of oil and 30 GToe of natural gas have been extracted (Martin-Amouroux, 2015; BP, 2019) i.e. about 210 Gt of hydrocarbons. To compensate the complex composition of oil and natural gas, one can assume these fossil hydrocarbons, including methane (CH4), composed of alkanes only, the general chemical formula of which is CnH2n+2 reasonably simplified to nCH2. Accordingly, 210 Gt of oil equivalent contain c.a. 180 Gt of carbon and 30 Gt of hydrogen. From the general equation CH2 + 3 O2 → CO2 + H2O + heat, 14 g of hydrocarbon (12 + 2) generates 44 g of CO2 (12 + 32) and 18 g of water (16 + 2), both compounds being hot. One can deduced that 210 Gt of hydrocarbons produced about 270 Gt of hot water. Based on the amount of water released from 28,000 Gt of ice lost between 1994 and 2017, the estimated 270 Gt of extra water cumulated since 1870 corresponds to c.a. 1 year of recent ice loss and, thus, it is rather small and negligible in terms of ocean level rise. However this hot water inserted 2.3 KJ/Kg/°C of heat in the environment, this heat being dispatched between biomass, atmosphere, and liquid water. Whether this liberated water played a role in the context of greenhouse gas is difficult to guess. Anyhow, the release of hot water from the combustion of oil and natural gas could become problematic if the production and the consumption of energy, fossil or not, continue to grow in parallel to the growth of the mammalian population (Zou et al., 2016).