Here's an interesting talk that suggests that we're not going to stay on the RCP8.5 scenario much longer even in the absence of any political action, but that emissions will go down simply due to geology.
http://www.resilience.org/stories/2014-02-25/oil-supply-and-demand-forecasting-with-steven-kopits
The presentation shows that we've had peak conventional oil in 2005. What he doesn't try to date, but which other people have tried, suggests we're looking at peak liquid fuels sometime between now and probably before 2017, maybe 2020, with peak natural gas and peak coal to follow before 2050.
My sense of the state of play is that we're not going to stay below 2 °C due to geology alone, though, so keep mitigating.
There are basically three complementary arguments why not everybody believes that there is enough coal for an RCP8.5 scenario:
The resource argument: A few decades ago, the reported coal reserves were huge, and they've been coming down much faster than the coal been used. One way to look at that is that countries used to find it advantageous to overreport reserves. The other way to look at it is that as more information has come in, the amount of coal that is technically and economically recoverable turned out to be lower. This is why I mentioned the estimate of peak coal around 2050
The energy argument: At the moment, coal receives a big energy subsidy from oil. Everything from mining, transport and manufacturing runs on oil, and as the oil goes away it's not at all clear that we can build a coal infrastructure using coal. Part of that is an energy returned on energy invested issue; there is even more disagreement about the EROEI of coal than there is about coal reserves. The question of EROEI is like fractional reserve banking: in an expanding economy it makes sense to do fractional reserve banking because it generates money that you can pay back with interest from the grown economy later. That's how we built the oil economy from a niche market replacing whale oil to what it was in 2005. But as Kopits points out, all the energy we produce at the moment is spoken for, so there's none left to build the coal infrastructure now, and I think Kopits also goes through the argument why this problem is going to get worse in the future (or if he doesn't then http://thearchdruidreport.blogspot.co.uk/ does).
The economic argument: As I noted above, the economic argument is a capital expenditure issue of the infrastructure: in an economy that is contracting because oil is going away and the capital that has been running the oil economy becomes worthless, it's not a given that we can afford to build the coal infrastructure. This is the basic asymmetry between a growing and shrinking economy: in a growing economy we had inflation. Because we were used to doing with less, we delayed using up the growth in production for a growth in consumption, and used the remainder for an increase in infrastructure, which concentrates wealth. In a shrinking economy as I said you can no longer afford to borrow from tomorrow because there's no longer the economic growth with which to pay back the interest, so inflation no longer means you can build the infrastructure. While if you have deflation, then you diffuse wealth, and the building of infrastructure requires a concentration of wealth. That's why capitalism and an exponential growth in energy consumption was such a politically successful combination. I'm not sure whether that means that the growth in the cooperative economy is significantly correlated with the slowed growth in energy consumption and is due to continue, but either way I don't think that means that if the cooperative economy really takes off we can expect a collective investment in the coal infrastructure either. Firstly, because I'd like to think that if that happens investment into a renewable infrastructure would have an equivalent EROEI. But more importantly, because everybody is used to their iPhone by now, so the 10%/a degrowth that Kevin Anderson says is needed doesn't seem to be gaining ground the way the cooperative economy does, with which delayed consumption now could give (y)our child(ren) global warming of less that 2 °C. Possibly that's also because it wouldn't be a temporary delay as in the past, but a permanent one.
