The 1,000 GtC Coal Question: Are Cases of High Future Coal Combustion Plausible?

Twenty years ago, legacy reserve-to-production (R-P) ratios of 300 or more indicated a possibility of vastly expanding global coal consumption. Studies of energy futures commonly adopted similar R-P values as equilibrium conditions, establishing coal as a virtually unlimited backstop supply for long-term scenarios. Yearly consumption and market prices for hard coal have doubled since 1990, calibrating the next century’s baseline. Over the same two decades, improving knowledge of global coal reduced estimates of total reserves by two-thirds, while costs increased much faster than anticipated by long-range coal resource models with long and flat supply curves. Consequently, the underlying assumptions for many future global energy projections no longer hold. Past coal-dominant projections of future global energy supply now significantly exceed modern assessments of the reserves recoverable under baseline trends and need to be revised. The energy system reference cases used for future greenhouse gas (GHG) emission pathways in climate change research are a case in point: baseline emission scenarios commonly project levels of coal combustion many times higher than current reserve estimates by the year 2100. In this paper, we explain why baselines depicting vast expansion in twenty-first century coal consumption should not be used as a business-as-usual assumption.