I think that the negotiators in Paris are pretty close to reaching an agreement (may have already done so). There’s a draft version here. Maybe the most interesting aspect of the agreement is the paragraph below:
Emphasizing with serious concern the urgent need to address the significant gap between the aggregate effect of Parties’ mitigation pledges global annual emissions of greenhouse gases by 2020 [and aggregate emission pathways] consistent with holding the increase in the global average temperature to well below 2oC above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5oC, recognizing that this would significantly reduce risks and impacts of climate change,
The holding the increase in the global average temperature to well below 2oC is itself quite strong, but pursuing efforts to limit the temperature increase to 1.5oC is quite remarkable.
In a sense, it’s impressive that they’re making such strong statements, but there is a concern that they could be meaningless. At 400ppm, the equilibrium temperature change is probably close to 1.5oC. Unless we can reduce emissions substantially, concentrations will continue to rise and we will likely exceed 1.5oC. Also, if we think that negative emissions are potentially extremely difficult, or even impossible, then the best we can do is halt all emissions, which would then stablisise temperatures.
Given the above, it would seem that limiting the temperature increase to 1.5oC would require getting emissions to zero within the next few decades, and there’s little I could find that indicates that this is recognised. The closest seems to be the paragraph below
In order to achieve the long-term global temperature goal set in Article 2 of this Agreement, Parties aim to reach the peaking of greenhouse house gas emissions as soon as possible, recognizing that peaking will take longer for developing country Parties, and to undertake rapid reductions thereafter towards reaching greenhouse gas emissions neutrality in the second half of the century on the basis of equity and guided by science in the context of sustainable development and poverty eradication.
If we think in terms of a carbon budget, then the carbon budget that will give us a 66% chance of staying below 2oC is around 300GtC. To stay below 1.5oC would require emitting – in total – considerably less than this. At current rates, we’d use it up in a couple of decades. If climate sensitivity is low, then we could emit more, but we’ll only know if that is the case, once we’ve done so.
Therefore, if we’re serious about limiting warming to 1.5oC, that would seem to require drastic emission reductions starting now, and there’s little to suggest that this is likely, even with this agreement. In a sense I’m reluctant to be too critical, given that it may well be the case that limiting warming to 2oC will be insufficient to avoid some of the more serious impacts. On the other hand, aspiring to something that you don’t actually try to achieve, seems meaningless.
Of course, maybe we’ll be lucky and we’ll develop alternatives that can replace fossil fuels very rapidly; maybe we’ll develop carbon capture and storage and/or negative emission technologies; maybe climate sensitivity will be low enough that can can overshoot the carbon budget without overshooting the warming target. However, as it stands right now, it seems that giving ourselves a reasonable chance of limiting warming to 1.5oC would require drastic emission cuts starting now.
Accepting such a target without also accepting this reality seems potentially counter-productive, especially as some people will be looking for any reason to find fault with this agreement. Of course, maybe I’m missing something, so I wrote this partly to see what other people think. Feel free to let me know via the comments.