A substantial portion of the carbon-based energy remaining the Earth's crust must stay there if society is to avoid the more serious consequences of future climate change.

About 321 petagrams of carbon (PgC) have been released to the atmosphere from the combustion of fossil fuels since 1750 (a petagram of carbon (Pg), also known as a Gigaton (Gt), is equal to 10¹⁵ grams or one billion tonnes).  We know with a high degree of certainty that the resulting increase in atmospheric greenhouse concentrations has contributed to the warming of the Earth, which in turn has caused rapid changes in many physical and biological systems.

How much carbon-based Energy remains in the Earth, and would happen if it were combusted and released to the atmosphere? Table 8.1 shows the estimated available amounts of nonrenewable carbon-based energy resources.  They amount to at least 284,000 exajoules (EJ).  By way of comparison, the world currently uses about 410 EJ per year of fossil fuels.  Substantial technological improvements would have to occur to make much of this resource economically viable, but the point here is there is a lot of carbon left in the ground. There is considerable uncertainty regarding the magnitude of remaining conventional oil and gas resources, as well as unconventional resources such as oil shale and coalbed methane.  To assess their general implications for climate change, however, the amount of uncertainty doesn’t really matter.

More than 100 countries have adopted a global warming limit of 2 °C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts and damages (Recall that the temperature of the Earth increased by about 0.74 °C over the past century).  What level of CO₂ emissions in the future would keep us below that 2 °C?  Recent research suggests that limiting cumulative CO₂ emissions over 2000–2050 to 1,000 Gt CO₂ yields a 25% probability of warming exceeding 2 °C—and a limit of 1,440 Gt CO₂ yields a 50% probability.  This suggests that less than half of the proven economically recoverable oil, gas and coal reserves can still be emitted up to 2050 to achieve such a goal.

The same point can be stated this way: Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO2), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 °C above pre-industrial temperatures.

The implications of this are clear: a substantial portion of remaining carbon-based-fuels need to remain in the ground if society wishes to avoid the more serious impacts associated with future climate change.

Sources

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