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Methane from food production might be the next wildcard in climate change
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Methane concentrations in the atmosphere are growing faster than any time in the past 20 years. The increase is largely driven by the growth in food production, according to the Global Methane Budget released today. Methane is contributing less to global warming than carbon dioxide (CO₂), but it is a very powerful greenhouse gas.
Since 2014, methane concentrations in the atmosphere have begun to track the most carbon-intensive pathways developed for the 21st century by the Intergovernmental Panel on Climate Change (IPCC).
The growth of methane emissions from human activities comes at a time when CO₂ emissions from burning fossil fuels have stalled over the past three years.
If these trends continue, methane growth could become a dangerous climate wildcard, overwhelming efforts to reduce CO₂ in the short term.
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In two papers published today (see here and here), we bring together the most comprehensive ensemble of data and models to build a complete picture of methane and where it is going – the global methane budget. This includes all major natural and human sources of methane, and the places where it ends up in methane “sinks” such as the atmosphere and the land.
This work is a companion effort to the global CO₂ budget published annually, both by international scientists under the Global Carbon Project.
Where does all the methane go?Methane is emitted from multiple sources, mostly from land, and accumulates in the atmosphere. In our greenhouse gas budgets, we look at two important numbers.
First, we look at emissions (which activities are producing greenhouse gases).
Second, we look at where this gas ends up. The important quantity here is the accumulation (concentration) of methane in the atmosphere, which leads to global warming. The accumulation results from the difference between total emissions and the destruction of methane in the atmosphere and uptake by soil bacteria.
CO₂ emissions take centre stage in most discussions to limit climate change. The focus is well justified, given that CO₂ is responsible for more than 80% of global warming due to greenhouse gases. The concentration of CO₂ in the atmosphere (now around 400 parts per million) has risen by 44% since the Industrial Revolution (around the year 1750).
While CO₂ in the atmosphere has increased steadily, methane concentrations grew relatively slowly throughout the 2000s, but since 2007 have grown ten times faster. Methane increased faster still in 2014 and 2015.
Remarkably, this growth is occurring on top of methane concentrations that are already 150% higher than at the start of the Industrial Revolution (now around 1,834 parts per billion).
The global methane budget is important for other reasons too: it is less well understood than the CO₂ budget and is influenced to a much greater extent by a wide variety of human activities. About 60% of all methane emissions come from human actions.
These include living sources – such as livestock, rice paddies and landfills – and fossil fuel sources, such as emissions during the extraction and use of coal, oil and natural gas.
We know less about natural sources of methane, such as those from wetlands, permafrost, termites and geological seeps.
Biomass and biofuel burning originates from both human and natural fires.
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Given the rapid increase in methane concentrations in the atmosphere, what factors are responsible for its increase?
Uncovering the causesScientists are still uncovering the reasons for the rise. Possibilities include: increased emissions from agriculture, particularly from rice and cattle production; emissions from tropical and northern wetlands; and greater losses during the extraction and use of fossil fuels, such as from fracking in the United States. Changes in how much methane is destroyed in the atmosphere might also be a contributor.
Our approach shows an emerging and consistent picture, with a suggested dominant source along with other contributing secondary sources.
First, carbon isotopes suggest a stronger contribution from living sources than from fossil fuels. These isotopes reflect the weights of carbon atoms in methane from different sources. Methane from fossil fuel use also increased, but evidently not by as much as from living sources.
Second, our analysis suggests that the tropics were a dominant contributor to the atmospheric growth. This is consistent with the vast agricultural development and wetland areas found there (and consistent with increased emissions from living sources).
This also excludes a dominant role for fossil fuels, which we would expect to be concentrated in temperate regions such as the US and China. Those emissions have increased, but not by as much as from tropical and living sources.
Third, state-of-the-art global wetland models show little evidence for any significant increase in wetland emissions over the study period.
The overall chain of evidence suggests that agriculture, including livestock, is likely to be a dominant cause of the rapid increase in methane concentrations. This is consistent with increased emissions reported by the Food and Agriculture Organisation and does not exclude the role of other sources.
Remarkably, there is still a gap between what we know about methane emissions and methane concentrations in the atmosphere. If we add all the methane emissions estimated with data inventories and models, we get a number bigger than the one consistent with the growth in methane concentrations. This highlights the need for better accounting and reporting of methane emissions.
We also don’t know enough about emissions from wetlands, thawing permafrost and the destruction of methane in the atmosphere.
The way forwardAt a time when global CO₂ emissions from fossil fuels and industry have stalled for three consecutive years, the upward methane trend we highlight in our new papers is unwelcome news. Food production will continue to grow strongly to meet the demands of a growing global population and to feed a growing global middle class keen on diets richer in meat.
However, unlike CO₂, which remains in the atmosphere for centuries, a molecule of methane lasts only about 10 years.
This, combined with methane’s super global warming potency, means we have a massive opportunity. If we cut methane emissions now, this will have a rapid impact on methane concentrations in the atmosphere, and therefore on global warming.
There are large global and domestic efforts to support more climate-friendly food production with many successes, ample opportunities for improvement, and potential game-changers.
However, current efforts are insufficient if we are to follow pathways consistent with keeping global warming to below 2℃. Reducing methane emissions needs to become a prevalent feature in the global pursuit of the sustainable future outlined in the Paris Agreement.
![The Conversation](https://counter.theconversation.edu.au/content/69894/count.gif)
Pep Canadell receives funding from the National Environmental Science Program - Earth Sciences and Climate Change Hub.
Ben Poulter receives funding from the United States National Science Foundation, the United State Geological Society, and the National Aeronautics and Space Administration.
Marielle Saunois a reçu des financements de la Commission Européenne.
Paul Krummel is employed by CSIRO and receives funding from MIT, NASA, Australian Bureau of Meteorology, Department of the Environment and Energy, and Refrigerant Reclaim Australia.
Philippe Bousquet a reçu des financements de la Commission Européenne
Rob Jackson receives funding from the U.S. National Science Foundation and Departments of Energy and Agriculture. He is a member of Stanford's Natural Gas Initiative, an industry affiliates program, working to reduce methane emissions.
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Originally published in the Manchester Guardian on 14 December 1916
Passing through the Severn Tunnel one got a strange contrast in weather. On the Welsh side mist, clinging, cold, dreary; on the English side hoar frost over the grass, a blue sky and hot sun overhead. The trees are bare now and showing their clean anatomy. Never are they more lovely than when one can see every finest twig outlined with characteristic gesture against the sky. Elms especially show to advantage when bare; where they have to be lopped for safety it is indeed a sore sight, for their habit of ending in a fine spreading plume is so individual and so beautiful. Along the banks of a canal the rows of pollard willows make quaint reflections in the still water. Farther on, by the river, the beech woods are grey, with scarcely a shade of brown from the tightly packed scrolls of buds. But the chestnut tips are thick and sticky, and it will be worthwhile cutting a few branches to put into water. Sprays of birch also may be treated in the same way, and it is a great joy to watch them unfold.
Continue reading...Why logs are twice as dirty as diesel
We think of wood burning as natural, but experiments show that wood smoke contains shocking levels of harmful particles
Walk round many suburbs on a winter’s night and your nose will tell you that wood burning is being used for home heating. A recent UK government survey found that 7.5% of UK homes now burn wood. The vast majority use it for supplementary heating or decoration. Wood burning is most popular in the south-east where it is used by around 16% of households and it is least popular in northern England and Scotland where it is used by less than 5%.
We think of wood burning as being natural and therefore less harmful to the environment when compared with fossil fuels. However, particle pollution from UK wood burning is now estimated to be more than double diesel exhaust.
Reduce EU quotas to stop overfishing | Letters
This week EU fisheries ministers meet to decide the north-east Atlantic fishing quotas for 2017 at their annual December conference. Let’s hope our minister, George Eustice, does not repeat his performance of last year, when – in the face of a desperate need to end overfishing – he acquired for the UK a 2016 quota that exceeded scientific advice by more than any other EU country and proclaimed this as a good deal. Overfishing is “a good deal” only for the short-term interests of the smallest but wealthiest sector of the fishing industry, whose mega-trawlers hoover up the stocks, destroy their habitats and exacerbate their chronic over-exploitation. It is to be hoped that Eustice will also conform to another requirement of the common fisheries policy – the provision of a greater share of the quota to the small, under 10-metre, boats that constitute the largest part of the fleet, fish more sustainably, employ more fishermen, provide real benefits for their communities and enhance their prospects of both survival and a renewed prosperity. While representing about 80% of the Welsh and English fleet, they have just 6% of the quota.
John Stansfield
Bristol
• Join the debate – email guardian.letters@theguardian.com
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The Clean Energy Finance Corporation has made a multi-million dollar loan for a new windfarm in Barnaby Joyce’s electorate.
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If you’re feeling unsettled by the Brexit/Trump future, consider this: since the 1950s humans have ramped up the pressure on the planet to such an extent that we have very likely propelled ourselves into a new geological epoch – the Anthropocene. Now that’s what geologists call change. The thing that freaks me out is that it’s rarely mentioned.
To unwrap that: for the past 10,000 years or so, we have hung out comfortably in what we call the Holocene epoch. During this period we have been able to rely on the Earth’s systems to dampen the effects of “forcings”. These are different factors that affect the Earth’s climate, such as volcanic eruptions and solar variations.
Continue reading...Australia's changing landscape through Google timelapse – video
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Google’s satellite timelapses show the inconvenient truth about our planet
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