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  Coal supply may be vastly overestimated
The world's coal supply suggests reserves may be vastly overestimated and we could be facing an unprecedented global energy crisis, according to a US expert.

On the flip side, a dwindling supply of coal could also throw the brakes on global warming, some argue.

Common knowledge about coal is that major producing nations like China, the United States and Australia, have enough to last hundreds of years, far beyond the reach of oil, which may already be in its twilight years.

But worldwide coal production could plateau as early as 2025, according to one new estimate, and a growing group of scientists are concerned that fossil fuel supplies may begin dwindling by mid-century.

Last year, David Rutledge of the California Institute of Technology analysed the coal production patterns of five regions around the world - eastern Pennsylvania, France, Germany's Ruhr Valley, the United Kingdom and Japan - each of which was producing at less than a tenth of its peak levels.

He found that each of the depleted regions followed a rough bell curve of production; initial production was followed by a steep ramp-up, a plateau near peak levels, and then a consistent decline.

When he applied the same formula to coal data from around the world, the results were startling.

The United Nations Intergovernmental Panel on Climate Change's maximum estimate for extractable coal is about 3000 billion tonnes. Rutledge's calculations suggest just 600 billion tonnes.

The problem with the IPCC estimate is that it lumps coal reserves, which are easy to mine, with coal resources, which may be impossible to mine.
Time for rethink

Rutledge's study also shows that, historically, national governments in the five regions have overestimated their reserves by a factor of four on average.

"These appraisals are large-scale issues," he says. "But they're done by governments. What's the incentive for governments not to give a number that is too high?"

James Murray of the University of Washington agrees.

In a talk being presented later this month at the American Geophysical Union Joint Assembly, he plans to call for a re-evaluation of IPCC emissions scenarios, all 40 of which overstate humanity's ability to emit the greenhouse gas carbon dioxide, according to Rutledge's numbers.

The committee's projections predict CO2 levels in the atmosphere to approach 500 parts per million by 2050, if emissions continue on their current trend.

But Rutledge's work suggest that even if humans burn all the coal and oil we can get our hands on, we won't be able to push CO2 past 450 ppm. Oil sands and other unconventional fossil fuels probably won't add much to that total.

Murray and Rutledge diverge on the question of climate effects, though.

Using IPCC models, Rutlgedge argues that global temperatures won't get higher than 2°C above pre-industrial levels, at the lower end of what scientists think might spark 'dangerous' climate change.

"We're still going to have global warming, and it's a serious threat," says Murray. "I have no doubt the IPCC dramatically underestimates climate sensitivity."

Regardless of climate impacts, the concern over looming energy scarcity may be more acute than ever.

"I think we'll see peak coal somewhere between 2025 and 2035," says Richard Heinberg of the Post Carbon Institute in California. "This has huge economic implications. Without growth in our energy supplies, it's very difficult to see how we're going to grow the economy."
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