The right way to understand the potential of unconventional fuels like methane hydrates and tight oil is to closely examine their production rates and their prices. If these fuels can be produced at large scales and profitable prices, they very well might influence geopolitics and economics in the ways that Charles C. Mann speculates in his recent Atlantic cover story. If they cannot, then it truly doesn't matter how much of those resources may exist underground and in the ocean floor.
Unfortunately Mann offers precious little data on price or production rates.
If Mann's data on methane hydrates is correct, then Japan's experiment so far has taken 10 years and $700 million to produce four million cubic feet of gas, which is worth about $16,000 at today's U.S. gas prices, or about $50,000 at today's prices for imported LNG in Japan. At this point, it is an enormously expensive experimental pilot project, and nothing more. We do not yet know when it might be able to recover commercial volumes of gas, or at what rate, or at what price. We have no reason to believe that if commercial quantities are recoverable by 2018 as Japan hopes--which seems incredibly optimistic--that the price of that gas will be competitive with imported LNG.
At the same time, we have numerous forecasts projecting that renewables like wind and solar will be competitive with fossil-fueled grid power in most of the developed world by 2020, including much of Asia. For example, a recent report by Citigroup, and another by researchers at Stanford University, among many others. A 2011 report by WWF and Ecofys projects that by 2018, solar PV will be the cheapest way to generate power in much of Asia. If these forecasts--based on more than a decade of real-world cost data for large-scale solar and wind are correct, then there is no reason to believe that gas from Japan's methane hydrate experiment will be able to compete with renewable grid power, which would constitute the largest market for that gas (unless Japan rapidly deploys natural gas vehicles in the interim, which it currently has no economic reason to do).
Mann also offers no data on tight oil production and price, but here are the key facts. In 2012, according to data from the U.S. Energy Information Administration, the U.S. consumed about 18.5 million barrels a day (mb/d) of liquid fuels and produced about 11 mb/d. Only about 7 mb/d of that 11 was actual crude oil, and about 1 mb/d of that was from tight oil. The non-crude liquids the US produced have less energy content than crude, and some of it cannot be made into vehicular fuel.
One cannot easily make a case for incipient U.S. "energy independence" on the basis of 1 mb/d of new tight oil production. A host of dubious assumptions and data distortions underlie the recent energy independence forecasts which I will not delve into here, but I have examined and debunked most of the reports that Mann cites, including those from the IEA (here and here), Ed Morse at Citigroup (here and here), and Leonardo Maugeri.
The progressive substitution of expensive unconventional oil for cheap conventional oil is a fundamental reason why the global price of oil has tripled over the past decade, and will continue to rise. This essential concept--along with the correct definitions of "conventional" and "unconventional"--is lost in Mann's treatment. It's absolutely true that we will never "run out" of oil--there will always be oil resources that are too expensive to produce that will stay in the ground--but since 2004 we have seen the undisputable evidence that affordable oil is slipping away from us, and that the rising price of oil has contributed to the stalling of the global economy. If the world could tolerate $300 a barrel, there might be no reason for concern about future oil supply. But it cannot. As the IEA's executive director recently noted, U.S. oil and gas prices need to go higher (through exports) to "avoid [the] shale boom turning to bust." But prices for refined products like gasoline and diesel are already near the upper limit for American consumers.