Final answer:
With the current pace of consumption, estimates suggest about 60 years of oil and 120 years of natural gas are left, whereas coal is more abundant with no immediate shortage. The reliance on fossil fuels is not sustainable long-term due to their finite nature and environmental costs, and alternatives including renewables are critical for a sustainable future.
Step-by-step explanation:
Based on current predictions, it is estimated that known reserves of petroleum will be exhausted in about 60 years, while natural gas supplies are estimated to run out in about 120 years. As for coal, this resource is much more abundant, constituting over 90% of the world's fossil fuel reserves, but is also more challenging to mine and transport. Despite being plentiful, coal is a solid, which makes it harder to extract and distribute than oil or natural gas.
Combining the finite nature of fossil fuels with their environmental impacts, it is apparent that we cannot rely on them indefinitely. In fact, 37% of the world's energy and 43% of the United States energy consumption currently depend on oil. Given the current world reserves of 1.3 trillion barrels, it is estimated there are about 45 years left of oil at the present rate of production. It is generally believed that peak oil production will be reached by the mid-21st century.
In terms of energy units, we have already consumed 8 ZJ (zettajoules) of oil, 4 ZJ of natural gas, and 8 ZJ of coal from initial reserves of 10 ZJ, 8 ZJ, and 20 ZJ respectively. This means that we have used a significant fraction of the planet's original fossil fuel endowment in just a couple hundred years. The future energy landscape remains uncertain, with a pressing need to transition to alternatives to fossil fuels, as highlighted in the recent chapters of the book. Therefore, exploring and investing in renewable energy sources is crucial to ensure a sustainable energy future.