Somewhere in the back of all our minds, we know that cows eat soya and soya and cows are grown where the Amazon rainforest used to be, and the Amazon is one of the last ecosystems controlling the overall Climate of the planet.
So we know beef ranching is intrinsically bad, whatever the discussion about cattle burps actually means.
But a brief dip into the news and views of animal husbandry science experts reveals that there is a very intense and ongoing argument about Methane from farmed animals, and what it implies for Global Warming, and my reaction is that we should make ourselves more aware.
The future looks AV – Almost Vegan.
Methane controls before risky geoengineering, please : 25 June 2009 by Kirk Smith : Magazine issue 2714
…Only about half the warming that has occurred up to now is due to CO2. The rest is caused by other greenhouse gases, particularly methane (Proceedings of the National Academy of Sciences, vol 97, p 9875). Similarly, less than half of the total warming expected over the next 20 years will be caused by CO2. Methane, along with other gases such as carbon monoxide, volatile organic compounds (VOCs) and black carbon particles, will cause most of the changes.
Recent modelling shows the way to have the biggest impact on warming over this century is to immediately reduce emission of these gases, and keep them low (International Journal of Climate Change Strategies and Management, vol 1, p 42).
Methane is a much more powerful greenhouse gas than CO2. A tonne of methane is responsible for nearly 100 times more warming over the first five years of its lifetime in the atmosphere than a tonne of CO2. Methane is removed from the atmosphere much more rapidly than CO2, with a half-life of 8.5 years compared with many decades for CO2, but a tonne of methane eventually turns to 2.75 extra tonnes of CO2 in the atmosphere. Even without taking this into consideration, a tonne of methane emitted today will exert more annual warming than a tonne of CO2 emitted today until 2075. Not until the year 7300 will the cumulative warming exerted by the two become equal. It is truly carbon on steroids.
…More serious attention to methane would also change the terms of climate change negotiations, possibly for the better. Taking methane into account would shift some of the burden of responsibility onto developing countries…
Why, then, are methane and the other non-CO2 greenhouse gases not more prominent in discussions over global warming? One reason is that the official weighting scheme to assess the relative impacts of greenhouse gases is out of date and too focused on long-term warming.
According to this scheme, a tonne of methane is equivalent to 21 tonnes of CO2 over a 100-year period. This is out of date – current estimates put the ratio at 25 or more. More importantly, the timescale is all wrong given the urgency we now face. It gives equal weight to measures that will reduce warming in 2109 and warming next year. This is a rather odd perspective: surely reducing next year’s warming should be the priority.
Reducing methane levels in the atmosphere would arguably be less painful than reducing CO2. The technology already exists, and reductions would be politically and economically easier to implement. Methane is also easier to handle in international negotiations than black carbon, the next most important non-CO2 greenhouse pollutant, because its impacts are better understood.
…Reducing livestock and rice production would require changes in consumption, but that is not the case with waste handling and leaks from fossil-fuel systems. Fixes for these do not directly threaten lifestyles and are amenable to direct regulation; no need for controversial carbon taxes or cap-and-trade schemes.
…This fruit is low-hanging, ripe and heavy with immediate benefits. Helping to pick it also means I can tell my grandchildren that, yes, I did do something to directly protect the planet.
[ Kirk Smith is professor of global environmental health at the University of California, Berkeley ]
Methane matters : 08 August 2009 : Magazine issue 2720
from Geoff Russell
Kirk Smith does a great job of explaining the importance of addressing emissions of all greenhouse gases rather than focusing exclusively on carbon dioxide (27 June, p 24).
According to the United Nations Food and Agriculture Organization, rice produces 19 per cent of global calories for its 34 megatonnes of methane, while ruminants produce just 1.7 per cent of global calories for 107 megatonnes.
Rice frequently feeds people who have few other choices, while big consumers of red meat generally have lots of food options. Beef in particular is also responsible for much of the world’s deforestation. The best course of action is clear: if it were not for the unhealthy and undue influence of the red meat industries on decision-makers in wealthy countries, that action would be immediate.
Saint Morris, South Australia
From Graham Faichney
Kirk Smith is right to point out that, in the atmosphere, a tonne of methane eventually turns to 2.75 extra tonnes of carbon dioxide (27 June, p 24).
However, he did not state that this applies only to methane from fossil sources. Biogenic methane, such as that emitted by livestock and rice paddies, represents the removal by photosynthesis of 2.75 tonnes of carbon dioxide from the atmosphere for every tonne of methane that is subsequently emitted when this plant material is broken down in the absence of oxygen. The methane breaks down in the atmosphere, with a half-life of 8.5 years, slowly returning the carbon dioxide to the pool from which it came.
Failure to allow for this difference between fossil and biogenic methane means that the contribution of methane to global warming has been overestimated, resulting in the demonising of agriculture, particularly its ruminant livestock industries.
Mosman, New South Wales, Australia
Kirk Smith writes:
It is true that biogenic methane does not add to net carbon dioxide in the atmosphere when it oxidises, but this does little to mitigate its warming impacts. The Intergovernmental Panel on Climate Change’s estimate of methane’s 100-year global warming potential, calculated relative to the effect of the same mass of carbon dioxide over that time, is 25. Taking biogenic origins into account only decreases this figure by 4 per cent, to 24. Alas, agriculture is not off the hook.
Biogenic And Fossil Methane Gwps Differ
Wed Aug 12 11:56:33 BST 2009 by Graham Faichney
Kirk Smith’s comment implies that the GWP of biogenic methane is the same as that of fossil methane. This is not consistent with the finding of the IPCC (1990, 1992) that the GWP of methane has two components, a direct component of 11 which applies to all methane and an indirect component, due to its breakdown products, which brings the total GWP to 21 and clearly applies only to fossil methane. The fact that biogenic methane removes CO2 from the atmosphere suggests that its direct GWP should be discounted by 2.75, not 1 as stated by Kirk Smith, as GWPs are mass factors. Thus the effective GWP for biogenic methane should be no greater than 11 rather than 21, the currently agreed value for accounting and reporting purposes, a value which overestimates the CO2-equivalent of biogenic methane and leads to the unfair demonising of the ruminant livestock industries. Agriculture should not be on “the hook”