Cows and Climate Change

There is no doubt the climate is changing. When I as a child, tornados happened in Kansas. Now they happen here with some sort of regularity, and we have had a sequence of ex-tropical cyclones and cyclones over summer. Things have to be done, but they have to be constructive. One problem is the issue can only be understood in terms of science and the level of scientific understanding with decision makers is abysmal. It is like asking the blind to sort out dangerous chemicals by reading the labels. Consider the issues of cows. Cows burp methane. Methane is a greenhouse gas. Therefore we need to eliminate cows. Pass the oatmilk.

A recent paper in Nature Geoscience (R. J. Allen, https://doi.org/10.1038/s41561-023-01144-z, 2023) appears to throw proverbial spanners in works relating to methane. Data suggests that since pre-industrial times, methane levels have risen from approximately 0,75 ppm to 1.8 ppm. I am sceptical of the first figure; how did they measure it then, and more interestingly, why did they measure it then? I dislike calculated figures because the calculations tend to be loaded with the bias of whoever does the calculations. If an assumption is required, it becomes a loaded one. However, if we accept those figures, models tell us this leads to an effective radiation forcing of just under half a watt per square meter. Thus methane is a serious problem, at least according to a disparate bunch that includes vegans, those who accuse dairy milk of causing cancer, and a group who protest just about everything. The problem is that ruminants, including cows, emit methane, so the argument goes that banning cows would go a long way to solving the problem.

However, methane has a relatively short lifetime in our atmosphere (about a decade), when it undergoes a sequence of oxidative changes that eventually lead to carbon dioxide and since all the carbon came from plant material, and hence the atmosphere, it is not clear to me that banning dairying would make much difference. The vegans probably also ignore the fact that more methane appears to come from rice paddies. I am not suggesting that we do nothing about the methane. Anything that reduces a greenhouse gas is useful.

However, the point of this paper is that methane is not as bad as current models suggest. Models that only focus on the longer wavelength greenhouse effects overestimate the effect of methane by about 30%. This is because methane absorbs short wavelength UV in the upper atmosphere, and causes photochemistry to make compounds that absorb further longer wave-length electromagnetic radiation. This cools the surface because the high energy photons convert their energy to heat when they reach the surface of the  planet. There is less heat if they don’t get there.

An even larger effect (approximately 60% offset) arises if we include enhanced cooling due to cloud rapid adjustments. We get increased lower altitude clouds, which enhance the reflection of short wavelength light, and we get decreased high level clouds, which enhances outgoing longer wavelength radiation. This does not mean methane is good; it remains a greenhouse gas, but what it means is that everything is far more complicated than most models accept. Also, it cannot hurt to reduce emissions. However, equally, the extremes promoted by the extreme protestors are simply not valid.

A second proposal (Schmitz et al.  Nature Climate Change https://doi.org/10.1038/s41558-023-01631-6 2023) may seem a little odd. The objective is to enhance carbon capture  and storage in plants, soils and sediments. They do this by protecting and restoring wild animals, and restoring their ecosystem. The argument is such an ecosystem contains more carbon than farmland, or worse, wasteland, or in one case, waste space. The way this works is that a diversity of animal species with medium to large bodies assist seed dispersal and germination of large-seeded trees with carbon-dense wood, herbivory that reduces  plant competition and increases soil nutrient supply and enhances soil carbon storage. In terms of increases of CO2 reduction, in Mt/year, wildebeests on the savannah will provide 4.4, the musk ox 30, the grey wolf 260, and the champions, fish, 5,500. By simply protecting species currently there we can secrete 5.8 Gt of CO2 / annum. By restoring species we can go further, again in Mt/a, the African elephant, 13, bison 595, and the total comes to 6.4 Gt/a. (If you notice the numbers don’t quite add up, that is because I left out minor contributions.) Now surely pastoral cows also increase soil nutrient supply and enhance soil carbon storage. It also shows it is necessary to consider the whole system, and not cherry pick the facts that strengthen your case.

None of this suggests that we do not have a problem with greenhouse gas emissions. What it does suggest is there may be a multitude of ways to solve the problem, and contributions can come from a variety of sources.

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Climate Change: Are We Baked?

The official position from the IPCC’s latest report is that the problem of climate change is getting worse. The fires and record high temperatures in Western United States and British Columbia, Greece and Turkey may be portents of what is coming. There have been terrible floods in Germany and New Zealand has had its bad time with floods as well. While Germany was getting flooded, the town of Westport was inundated, and the Buller river had flows about 30% higher than its previous record flood. There is the usual hand-wringing from politicians. Unfortunately, at least two serious threats that have been ignored.

The first is the release of additional methane. Methane is a greenhouse gas that is about 35 times more efficient at retaining heat than carbon dioxide. The reason is absorption of infrared depends on the change of dipole moment during absorption. CO2 is a linear molecule and has three vibrational modes. One involves the two oxygen atoms both moving the same way so there is no change of dipole moment, the two changes cancelling each other. Another is as if the oxygen atoms are stationary and the carbon atom wobbles between them. The two dipoles now do not cancel, so that absorbs, but the partial cancellation reduces the strength. The third involves molecular bending, but the very strong bond means the bend does not move that much, so again the absorption is weak. That is badly oversimplified, but I hope you get the picture.

Methane has four vibrations, and rather than describe them, try this link: http://www2.ess.ucla.edu/~schauble/MoleculeHTML/CH4_html/CH4_page.html

Worse, its vibrations are in regions totally different from carbon dioxide, which means it is different radiation that cannot escape directly to space.

This summer, average temperatures in parts of Siberia were 6 degrees Centigrade above the 1980 – 2000 average and methane is starting to be released from the permafrost. Methane forms a clathrate with ice, that is it rearranges the ice structure and inserts itself when under pressure, but the clathrate decomposes on warming to near the ice melting point. This methane has formed from the anaerobic digestion of plant material and been trapped by the cold, so if released we get delivered suddenly all methane that otherwise would have been released and destroyed over several million years. There are about eleven billion tonnes of methane estimated to be in clathrates that could be subject to decomposition, about the effect of over 35 years of all our carbon dioxide emissions, except that as I noted, this works in a totally fresh part of the spectrum. So methane is a problem; we all knew that.

What we did not know a new source has been identified as published in the Proceedings of the National Academy of Sciences recently. Apparently significantly increased methane concentrations were found in two areas of northern Siberia: the Tamyr fold belt and the rim of the Siberian Platform. These are limestone formations from the Paleozoic era. In both cases the methane increased significantly during heat waves. The soil there is very thin so there is very little vegetation to decay and it was claimed the methane was stored in and now emitted from fractures in the limestone.

The  second major problem concerns the Atlantic Meridional Overturning Circulation (AMOC), also known as the Atlantic conveyor. What it does is to take warm water that gets increasingly salty up the east Coast of the US, then switch to the Gulf Stream and warm Europe (and provide moisture for the floods). As it loses water it gets increasingly salty and with its increased density it dives to the Ocean floor and flows back towards the equator. Why this is a problem is that the melting Northern Polar and Greenland ice is providing a flood of fresh water that dilutes the salty water. When the density of the water is insufficient to cause it to sink this conveyer will simply stop. At that point the whole Atlantic circulation as it is now stops. Europe chills, but the ice continues to melt. Because this is a “stopped” circulation, it cannot be simply restarted because the ocean will go and do something else. So, what to do? The first thing is that simply stopping burning a little coal won’t be enough. If we stopped emitting CO2 now, the northern ice would keep melting at its current rate. All we would do is stop it melting faster.