Part of what makes debates about energy confusing to many is that the language of resource depletion allows one to make strong and accurate claims to justify widely divergent positions. Of course, we are running out of fossil fuels; they take millions of years to replace. Yes, we will never run out of fossil fuels; there will always be some amount that we will choose to leave in the ground because they are not worth extracting. You can logically say both or you can emphasize one. In any case, neither statement is helpful in getting to the core about why people care, and disagree, about energy, which has more to do with differences in values, appetite for risk, time horizons, as well as urgency of competing social priorities. Debates about energy poverty, climate change, and air pollution also have the requisite combinations of linguistic imprecision and real uncertainty to allow for strong conflicting claims.
The "are we running out?" framing distracts from two important points in Charles Mann's article. First, unconventional fossil fuels--fracking, tar sands, methane hydrates and several others--are growing in importance. Unconventionals comprise truly massive resources, but what makes them "unconventional" is that they are more dispersed than traditional fossil fuels. They are scattered around the world, they are difficult to reach, are mixed with other materials, and require much more processing to be useful. As a result they are almost invariably more expensive, more energy intensive, and more polluting than conventional fossil fuels. Adam Brandt at Stanford has probably done more than anyone in characterizing these resources.
Second, Mann's conclusion correctly focuses on the central policy challenge we confront. But let's be clear that this is not because environmentalists have banked on using resource depletion as the reason to address climate change. Energy security has at times been used as side effect of addressing climate change, but not as a central motivation. The more important policy issue that plentiful unconventionals bring up is the risk of myopia and over-reliance over the longer term. The policy challenge is about dealing with an array of persistent energy challenges--including access, air pollution, climate, and security--in a policy environment in which energy could become much less publicly salient than it has been in recent years.
These are important points in Mann's article. But in two ways--on climate and on energy security--the rise of unconventional changes things less.
Increased use of fracking and possibly methane hydrates does not change much on climate change. We were never on the verge of running out of fossil fuels--we have coal. Debates about coal reserves argue whether we have a 100 or 200-year supply. We have roughly 10 times as much carbon in coal in the ground as we can afford to put into the atmosphere without risking disruptive climatic consequences. Coal is cheap, easy to extract, and crucially, a large reliable domestic resource for key energy economies, notably China, India, and Russia as well as the U.S. Fracking and methane hydrates come on top of this. Coal has always been sufficient to destabilize the climate and undermine international agreements to reduce greenhouse gas emissions. Addressing climate change involves getting to a broad consensus, making it a sustained social priority, and adopting risk management perspective, perhaps aided by focusing events, interpretation of events as harbingers, valuing health co-benefits, and considering ethics. It's not something that resource depletion will force us into.
In the U.S., energy security is about using oil for transportation--and a lot has to change for natural gas to become an important transportation fuel. Natural gas accounts for 2% of U.S. transportation energy today, despite a unit of energy from oil costing about five times more than a unit of energy from natural gas. This could change, and is likely to if price spreads persist. But it will require the kind of transition in infrastructure and end-use technology that, as indicated by Prof. Smil, has occurred only slowly in the past; adoption of ethanol in Brazil is probably the fastest case. If it does change in a substantial way, then there is a real risk that all this natural gas will not be so cheap anymore. If 100s of millions of aspirational car drivers plan to fill up on compressed natural gas rather than gasoline then the story of abundance will quickly revert to one of scarcity.