Professor Barry McMullin:

I thank the Acting Chairman for his insightful comments and questions. He queried the emphasis on carbon dioxide. I said that in the case of carbon dioxide, we thought it should be done this way, but that was not intended to suggest that there is no issue, particularly with methane and nitrous oxide. We need broad action on all of them. The question of how to balance action on different pollutants is scientifically complex and I will not go into all the details here. In essence, however, carbon dioxide trumps everything else. If we do not get the carbon dioxide issue under control, it does not matter what we do with methane and nitrous oxide. There is a hierarchy of action here. We absolutely must act in respect of carbon dioxide. Acting effectively on methane and nitrous oxide buys us a little extra time, not a lot, to deal with carbon dioxide. It is time measured in a few years or decades, not time in terms of centuries. However, we need action on all climate pollutants, not just carbon dioxide.

In terms of the analysis of what the targets should be and what would be Paris alignment, it is a complex area. Coincidentally, I will be presenting at a conference next week on this subject, wearing my academic hat, as part of an EPA-funded project. A paper on that will be submitted for publication shortly and I will be delighted to share it with the committee as soon as it is fit to read. In essence, however, and getting slightly quantitative for a moment, in order to come up with a specific limit on how much carbon dioxide a particular country should permit itself - the structure of the Paris Agreement is bottom up - there is a scientific element and there is an ethical and value element. It is not a scientific answer. It depends. How much does one value other people who are not living here? How much does one value future generations? How much does one value the natural environment? These are ethical issues, so one cannot get a single scientific answer to that. However, one can set an overarching limit.

I will given my personal perspective on that. Taking what I regard as an absolutely minimal interpretation of global equity and a minimum deference to equity, which is basically to allocate every person living today in the world an equal share of the remaining carbon budget, and taking seriously the precautionary principle, which says that in view of scientific uncertainty one should act now on the basis of the conservative view of the science, and given the minimal interpretation of the Paris Agreement, which says we need to keep temperature rise definitely below 2°C over the pre-industrial, putting all of that together, one comes up with a remaining carbon dioxide budget for Ireland of roughly 400 megatonnes. This includes land use. It is net carbon dioxide from fossil energy, agriculture and carbon dioxide sequestered in land use, if there is any. That 400 megatonnes compares to current annual emissions in excess of 40 megatonnes. Basically, it is less than ten years. That is a minimal interpretation of all the things I mentioned.

Before we get into the ethical issues, I will quote David Roberts, an online environmental journalist, who said in the last week, "the chances of us overdoing it - trying too hard, spending too much money, reducing emissions too much or too fast - are effectively nil." There is no risk that we will do too much. Wearing my An Taisce affiliation hat, our impression in An Taisce - this is not unique to Ireland but it is particularly noticeable here - is that we seem to have a fixation on the risk that we will do too much, spend too much and overreact. From a scientific point of view, that ship has sailed. There is no possibility that we will overreact. Setting really strong targets for ourselves is a good faith contribution to the international agreement with which we have engaged. It is a collective action problem. We need support from our friends in Europe and globally. We have invested a huge diplomatic effort in the national interest around Brexit, but the threat of climate change puts Brexit in the penny place. We should be mobilising as much diplomatic effort as we can internationally, but we can only do that with any credibility if our diplomats can go abroad and say that we as a small nation - a rich nation but not very rich in certain senses - with very limited natural resources are doing our bit and this is how we are doing it. If we can say that, we can have influence on the European and global stages. However, if we cannot say that, we are contaminating and undermining international action and that will be bad for every other country in the world as well as ourselves. It is simply bad for us.