If everyone stopped giving a damn and no further action were taken, an additional 1.5-2.5 degrees by 2100 (~2.5-3.5 above 1900) would be the most likely range, from what I've seen. However, another one degree on top of that would likely be within an 80% confidence interval, and even two degrees on top of that (~5.5 above 1900) may well be closer to a 1% possibility than zero.
The cartoon in the OP does seem to be alarmist, and doesn't accurately reflect the IPCC reports. On current trends (ie, with considerable public interest/awareness and limited government investment in renewables, but so far without "prompt, aggressive limits on CO2 emissions") I'd be surprised if we managed to hit the IPCC's RCP6.0 scenario: And the median temperature projection for RCP6.0 is less than 3.2 degrees above 1900 by 2100.
So on current trends, best estimate is probably less than 3 degrees; if the 'sceptics' had their way and everyone stopped caring, probably more like 3.5 degrees. In either case, the 4-5 degrees claimed by the OP cartoon is misleading (though not impossible; just as a lot less is not impossible).