Final answer:
Known reserves of oil are projected to last about 60 years, natural gas about 120 years, and coal for several hundred years at current consumption rates. We have already used approximately half of the oil and gas reserves and less of coal. Extraction difficulties and increased consumption may alter these estimates, emphasizing the need for alternative energy sources.
Step-by-step explanation:
To answer the question of how long we can use proven reserves of each kind of fossil fuel at current rates of consumption, we need to look at the estimated reserves left and the current consumption rates. Currently, proven remaining reserves of oil, gas, and coal are 10, 8, and 20 zettajoules (ZJ) respectively. Considering the rates of consumption and known reserves, known reserves of petroleum are projected to last about 60 years, natural gas around 120 years, and coal is much more abundant than oil or gas, with a supply potentially lasting hundreds of years. However, it is important to note that these are conservative estimates and do not consider potential changes in consumption or discovery of new reserves.
When looking at the fraction of the original total fossil fuel resource already used, 8 ZJ of oil, 4 ZJ of gas, and 8 ZJ of coal have been utilized out of the original total reserves. This means approximately half of the oil and gas and a smaller fraction of coal resources have been consumed so far. The R/P ratio, which is the reserves to production ratio, provides an interesting insight into how long these resources will last at current consumption rates, but we must remember that extraction will likely become more difficult and expensive as we use up the more accessible deposits.
Moreover, the decline in fossil fuel availability will not be abrupt but will instead taper off over time as smaller and less accessible deposits become harder to extract. The use of fossil fuels is still increasing globally, posing a challenge for transitioning to alternative energy sources before the reserves are significantly depleted or become economically unviable to extract.