Professor Barry McMullin:

I thank Senator Daly. I have some general responses to his questions. On the issue of whether the Act should have been written differently, setting a separate budget for separate gasses would not have achieved what the Senator is hoping for in that the argument would just occur at the point of trying to enact that legislation. We would still have to make a trade-off and some decision about how to trade the contributions from action on different pollutants or gases. We would have had a similar discussion but it would have been even harder to resolve if it was written into legislation. The way the Act functions allows an ongoing discussion in five-year cycles about the contributions from different sectors. That said, this committee might want to consider the matter.

I am not a member of the Climate Change Advisory Council. In the course of the next three years leading up to the second cycle or the revisiting of the carbon budget programme for the follow five years, it might be helpful to invite the council to consider whether any refinements to the way the Act works domestically in Ireland might be appropriate, without compromising our participation in international reporting. There may be a case to be made for that. However, when it comes down to it, we are talking about trade-offs. The more we do in one area, the less we must do in another. On the Senator's specific question as to whether we could do more on carbon dioxide versus less on methane or vice versa, that can be assessed. Professor Allen has explained how the methodology his group has developed, GWP*, allows that trade-off to be assessed. I refer the Senator to the documentation I linked to in my submission on the work we have done in Dublin City University where we investigated precisely this in the case of Ireland. The problem is that there is only so much that can be don on carbon dioxide. Ireland has very high per capitaemissions relative to the global average and as a result, we rapidly run out of equitable space on a global basis for any further emissions of carbon dioxide. We will almost certainly still exceed our equitable budget of warming, even with the most rapid, or more rapid than is currently being contemplated, phasing out of fossil fuel use in Ireland. We will need to actively remove carbon dioxide from the atmosphere, which is a very expensive and not very well proven process depending on the approach taken. We will wind up having to do that. The question is how much of that we will have to do. The figure I mentioned of 50% methane reductions in Ireland by 2050 would be compatible with limiting our commitment to carbon dioxide removal to no more than 200 megatonnes over this century. That is net removals. Gross removals would probably be closer to double that. However, if we reduce methane by less than 50% by 2050, we are effectively committing to even more removals of carbon dioxide, if we are to play our equitable role.

Otherwise, we just give up and say the temperature is going to go above 1.5°C degrees and is going to stay above 1.5°C degrees. That is the hard choice we are now facing. These are trade-offs. There is no easy substitution between these things.