How much coal does the U.S. have?

The author of today’s post, Jeffery Greenblatt, Ph.D., is an expert on low-carbon energy technologies at Environmental Defense.

The U.S. may be short on oil and gas reserves, but the one energy source we thought we had in abundance was coal – enough to last 250 years at current consumption levels. Or so we thought.

A few weeks ago, the National Academy of Sciences (NAS) released a new report saying that U.S. coal reserves may last only another 100 years, or even less. That’s a big difference. How did we get this so wrong, and what are the implications for U.S. energy policy going forward?

Estimating coal reserves is not just a matter of assessing how much coal we have in the ground. Some coal can’t be mined due to economic, technical, legal and environmental limitations. The challenge is to estimate "recoverable resources" – coal that actually can be mined and sold.

The total amount of coal in the ground – or "identified resources" – is around 1700 billion tons. In the 1970s, the U.S. Department of Energy estimated that 16 percent of this – 270 billion tons – could be mined. But their estimation techniques were crude.

Recently the U.S. Geological Survey used much-improved estimation techniques to evaluate a sample of coal fields, and found that the recoverable-to-identified ratio varied from 5 to 25 percent. That’s a pretty big swing. We might be able to mine 16 percent of our coal, or we might be able to get at only 5 percent.

The NAS report said that until a comprehensive, modern survey is conducted of all U.S. coal reserves, it’s best to use the conservative 5 percent ratio. This yields about 85 billion tons of recoverable reserves, or 77 years at the current consumption rate of 1.1 billion tons per year.

There’s another reason to be conservative. The assumption that demand will stay at current levels is most likely incorrect. Demand for coal has roughly doubled since 1950, and projections by the U.S. Department of Energy suggest a similar trend into the future. In this case, assuming 5 percent access, our coal reserves would be exhausted in 50 years. This is a worst-case scenario, but unless demand declines dramatically, we still probably don’t have more than 100 years’ worth.

This has major implications for future U.S. energy policy under a carbon cap. We’ve been assuming that coal, in combination with CO₂ capture and storage technology, could supply U.S. energy needs for the foreseeable future. (It’s essential that the coal be used with CO₂ capture and storage technology to avoid the dangerous consequences of climate change.) But if we only have a 50 to 100 year supply, coal will have to be bridging strategy while new sources of energy are developed.