Professor Barry McMullin:

I thank the Chairman for the opportunity to provide evidence on the issues arising from the role of methane in climate policy design. I am a professor in the faculty of engineering and computing, DCU and research climate mitigation policy. I am accompanied remotely at today’s session by my colleague, Mr. Paul Price, who currently holds a research fellowship at DCU that was awarded by the Climate Change Advisory Council of Ireland.

We are here as independent academic researchers and do not speak on behalf of either DCU or the Climate Change Advisory Council. In the interest of time, I will shorten my remarks a little but my full statement is available to the committee.

We see the following points as key to ongoing assessment of the role of methane emissions in Irish climate policy. Ireland is a voluntary party to the Paris Agreement. This specifically includes the commitment to quantitative limits on global temperature rise. In Ireland's case, this has been transposed into domestic legislation through the Climate Action and Low Carbon Development (Amendment) Act 2021. The Act established a statutory national "carbon budget" framework and requires this to be implemented in a manner consistent with Ireland's equitable obligations under the Paris Agreement.

First and foremost, Ireland's carbon budgets must be designed and assessed by whether they represent an equitable contribution to meeting the Paris temperature rise goals. In the light of the rapidly destabilising global climate conditions, of which we are all aware, and the recent Intergovernmental Panel on Climate Change, IPCC, Special Report on Global Warming of 1.5^oC, this is now understood to mean limiting global temperature rise to 1.5^oC over pre-industrial levels with absolutely minimal overshoot of that level in either the amount of temperature rise or the duration of the overshoot.

The global scenarios assessed in the most recent IPCC assessment report 6 are unequivocal that meeting this temperature rise commitment requires rapid and deep cuts in the global emissions of all three of the most significant greenhouse gases that arise from human activities, which are: CO2, nitrous oxide and methane.

As members will have heard in the earlier session, there are technical and scientific issues that arise in assessing the temperature impacts from these different gases, particularly when they are combined into a single aggregate carbon budget for policy purposes, as under the Irish Act. The de facto approach to this uses a method referred to as the global warming potential over 100 years, or GWP100. The first Irish carbon budget programme has been expressed with this de facto method. However, it is widely recognised and well understood that this particular method, if used in isolation, may give a poor representation of the trade-offs in warming impact that are associated with the physical characteristics of the different gases. Of the three main greenhouse gases, this particularly affects methane. Indeed, this appears to be recognised in the Act, which requires appropriate consideration of the “distinctive” characteristics of methane. Unfortunately, the text of the Act qualified this further by referring to “biogenic” methane, which serves rather to obscure than to clarify. While there is a significant distinction in warming impact of methane versus the other gases, there is only a very minor and, effectively, immaterial distinction in warming impact between methane from biogenic versus non-biogenic fossil sources. That is true over the period of decades, say, 50 years ahead, that we are most acutely concerned with because that is when we have to limit and peak global temperature rise. This has led to some unnecessary confusion in the interpretation of the Act's provisions.

Nonetheless, it is very important to state that in developing the recommendations for the first carbon budget programme the Climate Change Advisory Council explicitly took account of these provisions in the Act. The council analysed the limitations of GWP100 aggregation in respect of how a mixed-gas budget relates to temperature impact. This work has been done. The council showed that with any fixed GWP100 budget that the temperature impact will vary significantly depending on exactly how that budget is distributed across the different gases. It presented a number of scenarios for this distribution. The council showed that those with relatively smaller budget allocations for methane, which is deeper reductions in methane, correspond directly to lower aggregate temperature impacts.

Separate work at DCU has investigated the warming impact of a wide variety of multi-gas greenhouse gas budget scenarios. We have used the method called GWP*, which was originally developed at the University of Oxford by Professor Myles Allen, from whom the committee has heard evidence this morning. To our knowledge, this was the first application of GWP* to examine multi-gas GHG budgets at a national level. In our most recent analysis we showed that there is a clear trade-off in Irish climate policy between the degree of reduction in annual emissions of methane and a tacit commitment to future, large scale net removals of CO₂. So the more reduction we make in ongoing emissions of methane then the less commitment we are making to removing CO₂ from the future and the less of an "I owe you" or IOU that we place on our young people today to remove CO₂in the future.

Based on particular criteria for alignment with the Paris Agreement temperature goals, and physical constraints on CO₂removal in Ireland, we estimate that the annual mass emissions of methane in Ireland would need to fall by about 50% by 2050, relative to 2018 levels, on the basis of an equitable contribution to meeting the temperature goals for Ireland. The faster this reduction in methane is achieved then the lower the risk of overshoot of the Irish contribution to global temperature rise. Please note that this still requires aggregate mass emissions of CO₂and nitrous oxide to be reduced by more than 100%, so methane by 50% and the aggregate of nitrous oxide and CO₂needs to be reduced by more than 100%, which is to go negative as emphasised by Professor Allen.

Some commentary on the distinctive characteristics of methane in general, and the GWP* methodology in particular, has suggested that it would be sufficient for Irish climate goals if annual mass emissions of methane were initially stabilised and then declined at a very slow rate of 3% per decade or 0.3% per annum. Unfortunately, this suggestion is based on a misleading conflation of climate stabilisation with meeting the temperature rise constraint. These are complementary but quite separate goals. While stabilisation is necessary but it is not sufficient in itself. We must stabilise at a temperature where meaningful and managed climate adaptation is still possible. We are seeing visibly how difficult that already is at the current level of temperature rise. This temperature limit is the overriding goal but to achieve same then it is absolutely essential that mass emissions of methane fall rapidly, and substantially, though not quite as fast or as deep as CO₂and nitrous oxide. This is true globally and especially true for Ireland because of its unusually large per capita emissions of methane. While improvements in methodology, metrics and calculation can help to refine the quantitative assessment of the required level of reduction, they do not alter the underlying physics.

In the specific case of Ireland, methane emissions are dominated by ruminant agriculture. The relationship with cattle numbers is complex but scales very directly with total output, which is litres of milk and kilos of beef. This has been clearly apparent during the recent rapid and policy-led expansion in dairy production. Previous evidence to this committee from Mr. Price has addressed this in more detail and will not be repeated here. We would simply emphasise that we sympathise greatly with the committee in confronting the distinctive and systemic challenges now facing this sector in Ireland. We would not seek in any way to downplay the difficulties involved. However, we emphasise that, as has been manifest in recent extreme weather events on a global basis, the physical climate system is, unfortunately, entirely indifferent to these difficulties. It will not respond to our aspirations but only to our actions and specifically to our ongoing emissions of greenhouse gases.

We look forward to addressing any questions that committee members may have.