Kevin Bullis has written a smart piece at MIT Technology Review about how mankind is likely to blow by the 1-trillion ton carbon budget. Realistically, it will be difficult to stay within budget and avoid warming beyond 2C (what is generally considered the threshold). Based on previous large-scale energy transitions (Bullis cites the French transition to nuclear over several decades), it is a slow and difficult process. Time we might not have: Myles R. Allen, a scientist at the University of Oxford and one of the authors of the IPCC report, thinks we’ll hit that trillionth ton around 2040.
It won't be difficult to blow by the 1-trillion ton threshold based on the amount of fossil fuels still in the ground. As Amy Myers Jaffe remarks, "scarcity will not be the force driving a shift to alternative energy. Climate and energy policy initiatives will have to take into consideration the possibility of oil and gas surpluses and lower fossil fuel prices."
The lesson here is that the economics are still in favor of producing fossil fuels. The cyclical nature of energy prices suggests that higher prices will spur development of technologies to reach more difficult energy deposits. This doesn't mean that oil and natural gas prices will be low for the rest of time, but it does reflect how high energy prices in the 2000s led not only to funding and research in alternative fuels (particularly biofuels), but also in oil and gas technologies. This investment coupled with decades of U.S. government and academic research proved fruitful with the combination of horizontal drilling and hydraulic fracturing becoming a deployable technology.
We have now entered a period of energy surplus where we produce energy from "unconventional sources" using technological breakthroughs like horizontal drilling and hydraulic fracturing in places like North Dakota, south Texas, Lousiana, and Pennsylvannia. (and soon to be California?).
We're still in the early stages with unconventional fuels. As Charles C. Mann articulated in his story for The Atlantic: "we will never run out of oil." Now, "never" isn't the word I would choose, but in the time scales that we're concerned with (years, decades, centuries), I'm inclined to side with Mann: there are plenty of fossil fuels in the ground (and under the sea if you consider methane hydrates). Before long, unconventional fuels will be considered conventional. And we haven't even tapped into what's recoverable with heating actual shale deposits for fuel.
If the world should be decarbonizing, and rather quickly according to the latest IPCC report (again, 1-trillion ton budget!), a surplus of fossil fuels is not exactly the news you want to hear.
From a technical perspective, displacing fossil fuels is difficult. To have a disruption you need a technology or fuel source that is not just as good, but better. Whatever replaces fossil fuels will have to do a better job at providing useful work by being cleaner, by having greater energy density, etc. Is this electricity from renewable sources? Is this electric vehicles and grid storage and an intelligent Internet of Things? Maybe. Sure. Who knows. We'll see. Yes.
The decision is ours then, not on geology or other natural constraints. It's up to us to craft policies, develop trade agreements, or implement technologies that keep us within our carbon budget in a period of fossil fuel abundance.