The reason that 2 degree climate change target should be ditched being that it was always an entirely economically illiterate target to set in the first place. Sadly, that's not the point being made in Nature on it. As The Guardian reports:

But two academics in the prestigious journal Nature now argue that the 2C target has outlived its usefulness. They say it should be abandoned and replaced with a series of measures – “vital signs” of the planet’s health.

Under the headline, “Ditch the 2C warming goal”, they argue the 2C limit is “politically and scientifically ... wrong-headed”, it is “effectively unachievable” and it has let politicians off the hook, allowing them to “pretend that they are organising for action when, in fact, most have done little.”

The reason it should be ditched is that it should never have been a target in the first place. For we should not be trying to target a particular change in temperature: we should be trying to target a certain cost of action.

Think back to what every economic report on this issue has said. That there will be costs associated with allowing climate change to happen. Also that there will be costs with preventing climate change from happening. And in such circumstances the correct answer is that we should spend up to the price of those costs on trying to prevent it happening. But we should not spend more than those costs: nor, obviously, should we spend less.

Thus whatever climate change target is set (for those who want to set one at all) it always has to be set in terms of the costs of the actions we are going to take. And this does have very important effects. For example, if we attack the problem in the most efficient manner possible (say, a carbon tax) then we can avert more climate change by doing so than if we try to avert it in less efficient manners (say, regulation or legislation). And that's why we really do want to always keep the costs in mind. Because if we set a temperature target, as we have, then people will say that we should do anything at all to meet that temperature target. But that's the very thing that we've already proven is not true: we should not do anything at all to avert warming. We should only do however much is economically rational: which brings us back to the costs of action as against the benefits of it.

So ditch the two degrees by all means. Then concentrate on what actually matters: the costs of whatever actions are taken.