Professor Peter Thorne:

I will give an abridged version of my note because the committee has it and I will highlights some matters in the interests of time.

My first point is that methane is one of three well mixed greenhouse gases that have varied naturally over millennia and longer. We can measure for 800,000 years measuring them over successive glacials when great ice caps cover North America and Eurasia and interglacials such as now. The difference in methane concentration is of the order of between 200 to 400 parts per billion.

Since 1750, methane concentrations have increased by more than 1,000 parts per billion and climbing.

This is not normal. This is part of human interference in the methane cycle. We know where it comes from. We also know it comes from fossil fuels, ruminants, paddy rice fields and waste. Those are the principal sources of that methane. We also know that the elevated greenhouse gas burdens, principally CO2, methane and nitrous oxide, are responsible for the approximate 1.1°C of warming we have seen to date. As members have heard, methane does differ from the other gases. It is a much shorter lived gas. It is also a much more powerful gas. It is the difference between effectively flow forcer, which is something you can turn on and off very quickly, versus a stock forcer. If you like, it is the difference between an electric heater that can be turned on at the wall and a night storage heater. We can think of methane as the electric heater that we can switch on and off very quickly and the other much longer greenhouse gases as the night storage heater, which warms up once we have turned it on. That means we have a unique opportunity, scientifically-speaking, with methane to turn the heat down that much more quickly. This is important because if we are to avoid the worst impacts of warming and keep to 1.5°C we have to reduce methane abundance in the atmosphere while simultaneously - this is a key point - driving CO2 to net zero. We do not stop warming unless we get CO2 to net zero. We must not let methane confuse us from the ultimate aim which is to get to net zero on CO2.

It is important to note that if we had started seriously on our climate change mitigation efforts globally 30 years ago, we would have a whole range of different options now. In some sense, why methane is important now is that we are so close to 1.5°C. We prevaricated, waited and wanted to continue to burn fossil fuels for so long that if we are to keep to 1.5°C we now have little option but to play with the methane in addition to the longer lived greenhouse gases to attain that effort. My colleague, Dr. Rogelj, will speak further to that. As has been noted, the legislation speaks to the special circumstances of biogenic methane and methane more general. Biogenic methane is distinct in no way while it is in the atmosphere. While it is emitted and in the atmosphere and causing the warming it is no different at all. The difference arises from the active component of the carbon cycle. Once the methane disappears and methane's half life is approximately 12 years, which means if I emit a tonne today, half of that tonne remains in 12 years, a quarter remains in about 24 years, etc., by a century, there is a none left effectively, to all intents and purposes. A fossil methane, something from gas extraction, fracking, mining, etc., is a new addition of carbon to the cycle so it hangs around as an additional CO2 burden. It is equivalent to burning fossil fuels and releasing CO2, but it has the added penalty for the first number of years of creating greater warming. That is the difference there.

Quite rightly, policy requires consideration of the relative efficacy of different options in mitigating the impacts of climate change. I think we can all agree on that. We can also agree that methane has a different set of properties. Where there is disagreement is where fundamentally the physics ends and the politics and policy takes over. How do we take that? That is embedded in a bunch of assumptions around the immediacy of our climate goals and their relative importance; historical responsibility or grandfathering. We should be honest with ourselves: The natural state of Ireland's ruminant population would be pretty close to zero and not the almost 7 million we have. We must also be honest with how we ensure equity between different countries and within communities in terms of the appropriateness of policy targets. These can all lead to very different and differing opinions as to what the correct course of action is. As a scientist, I can tell the committee about the physics and the problems. I cannot tell it the solutions because that is not my job as a scientist. I would like to state on the GWP100 that there is a big problem if we choose to not report in that metric. As Professor Allen said earlier, it is fine, and I would welcome reporting in additional metrics, but for the purposes of the EU's Fit for 55 and UNFCCC, we will be forced to report in GWP100, whether we like it or not. The risk of going our own way in our national approach is that we if end up diverging we would potentially end up with huge penalties in some way or other. I would like to see it change. I think there is a groundswell of opinion that we should treat short-lived forces differently from long-lived forces. That should be done internationally and we should look at it then in terms of cascading it here. A single country cannot do it the opposite way around.

Finally I would like to make a couple of points more broadly than on methane. I despair of how the mitigation conversation in this country centres within its second or third question on agriculture. As the late great Douglas Adams would say, it is making it somebody else's problem for the vast majority of the population who are not farmers. If farmers were successful in getting to net zero, we would still miss our 51% reduction target because two thirds of our emissions arise from the non-agricultural sectors. We need to be honest with citizens. We need to make sure that we have action across all sectors. If we are going to have action across agriculture - we need it to play its part - it must be a meaningful and effective just transition that protects farmers and reinvigorates rural communities, opening up new markets and opportunities for them. I believe there is that opportunity space. I fundamentally believe in the ingenuity and adaptability of our agricultural sector, if appropriately enabled, to address the mitigation challenge before us, but we need to stop playing around and telling farmers every second year to do something different. They need stability to have the decision-making. They need the certainty to make choices that are viable for their businesses. We cannot tell them to stop producing milk, start producing milk, stop producing milk. This is madness. We need stability in policy so that they can make the right choices. We need to open up opportunities to this sector.