No matter when you believe global oil production will reach its peak and begin its inevitable decline, don't believe it will help humanity stop the burning of fossil fuels that contribute to global climate change.

Why? Coal, the dirtiest fossil fuel, is far more plentiful than oil is or ever will be. Turning to coal as a replacement transportation fuel would lead to an even greater amount of greenhouse-gas emissions, and thus a greater threat of global climate change.

That's the view of scientists discussing the relationship between "peak oil" and climate change Wednesday at the American Geophysical Union's fall meeting in San Francisco. The gathered scientists are seeking to predict what could happen after global oil production reaches its peak oil point – the maximum level of global oil production, which some studies say is decades away, and others say is happening right now.

"Will the end of oil usher in a century of coal, or will it usher in a transformation to low-carbon technologies?" asked Ken Caldeira, from the Carnegie Institution at Stanford University. "If we don't electrify or otherwise transform our transportation sector, the need for liquid fuels could lead to an increase in coal liquefication."

Making liquid transportation fuel from coal is a well-known process – Nazi Germany used coal-to-liquid fuels to power its war machine. But not only is coal a dirtier fuel than oil from a greenhouse-gas emissions perspective, making it into liquid fuel also involves the use of additional energy, making it "a double whammy" for global warming, Caldeira said.

The problem becomes more pressing given that burning coal for electricity production and other purposes is already expected to be the major contribution to future greenhouse gas emissions, said Pushker Kharecha, an associate research scientist with NASA's Goddard Institute for Space Studies and the Columbia University Earth Institute.

"Coal to liquids must not be used as large scale substitutes for dwindling oil and gas" when those become scarce, "unless all such emissions form them are captured and stored," he said. But capturing, or sequestering, carbon from coal plants is still far from mass adoption (see Canada to Beat U.S. to Carbon Storage and Vattenfall to Trap Carbon Emissions).

Preventing more emissions is critical, Kharecha said, because the levels of carbon dioxide that currently exist in the atmosphere are already higher than they should be to combat global warming, according to a paper published a few weeks ago Kharecha co-wrote with James Hansen, the head of NASA's Goddard Institute for Space Studies and a well-known climate change scientist.

The paper argues that atmospheric carbon dioxide levels need to be brought down to 350 parts per million, rather than the more common target of 450 parts per million, Kharecha said. Current levels are about 385 parts per million, he said.

"Returning carbon dioxide to 350 parts per million by this century is still feasible," he said. But a key part of getting there would be to phase out all emissions from coal by 2030, he said.

That "will take Herculean efforts, really," including a massive shift to renewable energy sources in the short term and an increase in the use of nuclear power, as well as carbon sequestration for remaining coal-fired power plants, in the longer-term, he said.

It will also require a tax on carbon dioxide emissions, he added – a concept that has met with resistance from industries that prefer cap-and-trade systems to reduce emissions (see Carbon Tax a Better Idea? and U.N. Climate Talks Pose Big Impact on Greentech).

Thus, in terms of their effects on global warming, "oil and gas by themselves don't have enough carbon to take us into the dangerous zone for very long, because they just peter out," Kharecha said. "But that's assuming we do something about coal."

Tags: coal, liquidfuel, nazigold, oil, peakoil