The 2C temperature rise doesn't account for possible growth in CO2 and methane emissions and it certainly doesn't account for the release of legacy stores of both gases in the arctic ice, as we've no idea how bad that could get and the models are only being done now. There's a good chance that even if human beings keep CO2 production steady or cut it while ignoring methane, or even if they cut both while failing to counteract natural stores of greenhouse gases being released by the damage already done, that the 2°C mark could be well surpassed. That's what the new scientist article is about.