We found methane-eating bacteria living in a common Australian tree. It could be a game changer for curbing greenhouse gases

Luke Jeffrey, Southern Cross UniversityTrees are the Earth’s lungs – it’s well understood they drawdown and lock up vast amounts of carbon dioxide from the atmosphere. But emerging research is showing trees can also emit methane, and it’s currently unknown just how much.

This could be a major problem, given methane is a greenhouse gas about 45 times more potent than carbon dioxide at warming our planet.

However, in a world-first discovery published in Nature Communications, we found unique methane-eating communities of bacteria living within the bark of a common Australian tree species: paperbark (Melaleuca quinquenervia). These microbial communities were abundant, thriving, and mitigated about one third of the substantial methane emissions from paperbark that would have otherwise ended up in the atmosphere.

Because research on tree methane (“treethane”) is still in its relative infancy, there are many questions that need to be resolved. Our discovery helps fill these critical gaps, and will change the way we view the role of trees within the global methane cycle.

Wait, trees emit methane?

Yes, you read that right! Methane gas within cottonwood trees was first reported in 1907, but has been largely overlooked for almost a century.

Only in 2018 was a tree methane review published and then a research blueprint put forward, labelling this as “a new frontier of the global carbon cycle”. It has since been gaining rapid momentum, with studies now spanning the forests of Japan, UK, Germany, Panama, Finland, China, Australia, US, Canada, France and Borneo just to name a few.

Research on tree methane is still in its relative infancy.

In some cases, treethane emissions are significant. For example, the tropical Amazon basin is the world largest natural source of methane. Trees account for around 50% of its methane emissions.

Likewise, research from 2020 found low-lying subtropical Melaleuca forests in Australia emit methane at similar rates to trees in the Amazon.

Dead trees can emit methane, too. At the site of a catastrophic climate-related mangrove forest dieback in the Gulf of Carpentaria, dead mangrove trees were discovered to emit eight times more methane than living ones. This poses new questions for how climate change may induce positive feedbacks, triggering potent greenhouse gas release from dead and dying trees.

Aerial shot of river through trees in the Amazon — Trees account for around 50% of the total Amazon basin methane emissions.
Shutterstock

Treethane emissions most likely account for some of the large uncertainties within the most recent global methane budget, which tries to determine where all the methane in the atmosphere comes from. But we’re still a long way from refining an answer to this question. Currently, trees are not yet included as a distinct emissions category.

So where exactly is the treethane coming from?

Within wetland forests, scientists assumed most treethane emissions originate from the underlying soils. The methane is transported upwards via the tree roots and stems, then through to the atmosphere via their bark.

We confirmed, in other recent research, that wetland soils were indeed the source of methane emissions in lowland forest trees. But this wasn’t always the case.

Some lowland forest trees such as cottonwood can emit flammable methane directly from their stems, which is likely produced by microbes living within the moist trees themselves. Dry upland forest trees are also emerging as methane emitters too — albeit at much lower rates.

Paperbark trees surround a body of water — Paperbark forest in a wetland, where bark-dwelling methane-eating microbes were discovered.
Luke Jeffrey, Author provided

Discovering methane-eating bacteria

For our latest research, we used microbiological extraction techniques to sample the diverse microbial communities that live within trees.

We discovered the bark of paperbark trees provide a unique home for methane-oxidizing bacteria — bacteria that “consumes” methane and turns it into carbon dioxide, a far less potent greenhouse gas.

Remarkably, these bacteria made up to 25% of total microbial communities living in the bark, and were consuming around 36% of the tree’s methane. It appears these microbes make an easy living in the dark, moist and methane-rich environments.

This discovery will revolutionise the way in which we view methane emitting trees and the novel microbes living within them.

Only through understanding why, how, which, when and where trees emit the most methane, may we more effectively plant forests that effectively draw down carbon dioxide while avoiding unwanted methane emissions.

Author sampling microbes from paperbark tree — Microbe sampling techniques have advanced within the last few decades, allowing us to understand the diverse microbial communities living within trees.
Luke Jeffrey, Author provided

Our discovery that bark-dwelling microbes can mitigate substantial treethane emissions complicates this equation, but provides some reassurance that microbiomes have evolved within trees to consume methane as well.

Future work will undoubtedly look further afield, exploring the microbial communities of other methane-emitting forests.

A trillion trees to combat climate change

We must be clear: trees are in no way shape or form bad for our climate and provide a swath of other priceless ecosystem benefits. And the amount of methane emitted from trees is generally dwarfed by the amount of carbon dioxide they will take in over their lifetime.

However, there are currently 3.04 trillion trees on Earth. With both upland and lowland forests capable of emitting methane, mere trace amounts of methane on a global scale may amount to a substantial methane source.

As we now have a global movement aiming to reforest large swaths of the Earth with 1 trillion trees, knowledge surrounding methane emitting trees is critical.

Luke Jeffrey, Postdoctoral Research Fellow, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Half of global methane emissions come from aquatic ecosystems – much of this is human-made

Judith Rosentreter, Yale University; Alberto Borges, Université de Liège; Ben Poulter, NASA, and Bradley Eyre, Southern Cross UniversityMethane — a greenhouse gas far more potent than carbon dioxide — plays a major role in controlling the Earth’s climate. But methane concentrations in the atmosphere today are 150% higher than before the industrial revolution.

In our paper published today in Nature Geoscience, we show as much as half of global methane emissions come from aquatic ecosystems. This includes natural, human-created and human-impacted aquatic ecosystems — from flooded rice paddies and aquaculture ponds to wetlands, lakes and salt marshes.

Our findings are significant. Scientists had previously underestimated this global methane contribution due to underaccounting human-created and human-impacted aquatic ecosystems.

It’s critical we use this new information to stop rising methane concentrations derailing our attempts to stabilise the Earth’s temperature.

From underwater sediment to the atmosphere

Most of the methane emitted from aquatic ecosystems is produced by micro-organisms living in deep, oxygen-free sediments. These tiny organisms break down organic matter such as dead algae in a process called “methanogenesis”.

Flooded rice paddies — Rice farming releases more methane per year than the entire open ocean.
Shutterstock

This releases methane to the water, where some is consumed by other types of micro-organisms. Some of it also reaches the atmosphere.

Natural systems have always released methane (known as “background” methane). And freshwater ecosystems, such as lakes and wetlands, naturally release more methane than coastal and ocean environments.

Human-made or human-impacted aquatic ecosystems, on the other hand, increase the amount of organic matter available to produce methane, which causes emissions to rise.

Significant global contribution

Between 2000 and 2006, global methane emissions stabilised, and scientists are still unsure why. Emissions began steadily rising again in 2007.

There’s active debate in the scientific community about how much of the renewed increase is caused by emissions or by a decline of “methane sinks” (when methane is eliminated, such as from bacteria in soil, or from chemical reactions in the atmosphere).

We looked at inland, coastal and oceanic ecosystems around the world. While we cannot resolve the debate about what causes the renewed increase of atmospheric methane, we found the combined emissions of natural, impacted and human-made aquatic ecosystems are highly variable, but may contribute 41% to 53% of total methane emissions globally.

In fact, these combined emissions are a larger source of methane than direct anthropogenic methane sources, such as cows, landfill and waste, and coal mining. This knowledge is important because it can help inform new monitoring and measurements to distinguish where and how methane emissions are produced.

Water is a big part of much of our landscape, from mountain rivers to the coastal ocean. This aerial image shows Himalaya rivers, wetlands, lakes and ponds, and the world’s largest mangrove forest (the Sundarbans) at the coast of the tropical Bay of Bengal.
George Allen, Author provided

The alarming human impact

There is an increasing pressure from humans on aquatic ecosystems. This includes increased nutrients (like fertilisers) getting dumped into rivers and lakes, and farm dam building as the climate dries in many places.

In general, we found methane emissions from impacted, polluted and human-made aquatic ecosystems are higher than from more natural sites.

For example, fertiliser runoff from agriculture creates nutrient-rich lakes and reservoirs, which releases more methane than nutrient-poor (oligotrophic) lakes and reservoirs. Similarly, rivers polluted with nutrients also have increased methane emissions.

An aquaculture farm — Coastal aquaculture farms emit up to 430 times more methane per area than coastal habitats.
Shutterstock

What’s particularly alarming is the strong methane release from rice cultivation, reservoirs and aquaculture farms.

Globally, rice cultivation releases more methane per year than all coastal wetlands, the continental shelf and open ocean together.

The fluxes in methane emissions per area of coastal aquaculture farms are 7-430 times higher than from coastal habitats such as mangrove forests, salt marshes or seagrasses. And highly disturbed mangroves and salt marsh sites have significantly higher methane fluxes than more natural sites.

So how do we reduce methane emissions?

For aquatic ecosystems, we can effectively reduce methane emissions and help mitigate climate change with the right land use and management choices.

For example, managing aquaculture farms and rice paddies so they alternate between wet and dry conditions can reduce methane emissions.

Restoring salt marsh and mangrove habitats and the flow of seawater from tides is another promising strategy to further reduce methane emissions from degraded coastal wetlands.

We should also reduce the amount of nutrients coming from fertilisers washing into freshwater wetlands, lakes, reservoirs and rivers as it leads to organic matter production, such as toxic algal blooms. This will help curtail methane emissions from inland waters.

These actions will be most effective if we apply them in the aquatic ecosystems that have the greatest contribution of aquatic methane: freshwater wetlands, lakes, reservoirs, rice paddies and aquaculture farms.

This will be no small effort, and will require knowledge across many disciplines. But with the right choices we can create conditions that bring methane fluxes down while also preserving ecosystems and biodiversity.

Judith Rosentreter, Postdoctoral Research Fellow, Yale University; Alberto Borges, Research Director FRS-FNRS, Associate Professor at ULiège, Université de Liège; Ben Poulter, Research scientist, NASA, and Bradley Eyre, Professor of Biogeochemistry, Director of the Centre for Coastal Biogeochemistry, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: methane is short-lived in the atmosphere but leaves long-term damage

Zebedee Nicholls, University of Melbourne and Tim Baxter, University of Melbourne

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz

Methane is a shorter-lived greenhouse gas – why do we average it out over 100 years? By doing so, do we risk emitting so much in the upcoming decades that we reach climate tipping points?

The climate conversation is often dominated by talk of carbon dioxide, and rightly so. Carbon dioxide is the climate warming agent with the biggest overall impact on the heating of the planet.

But it is not the only greenhouse gas driving climate change.

Comparing apples and oranges

For the benefit of policy makers, the climate science community set up several ways to compare gases to aid with implementing, monitoring and verifying emissions reduction policies.

In almost all cases, these rely on a calculated common currency – a carbon dioxide-equivalent (CO₂-e). The most common way to determine this is by assessing the global warming potential (GWP) of the gas over time.

The simple intent of GWP calculations is to compare the climate heating effect of each greenhouse gas to that created by an equivalent amount (by mass) of carbon dioxide.

In this way, emissions of one gas – like methane – can be compared with emissions of any other – like carbon dioxide, nitrous dioxide or any of the myriad other greenhouse gases.

These comparisons are imperfect but the point of GWP is to provide a defensible way to compare apples and oranges.

Limits of metrics

Unlike carbon dioxide, which is relatively stable and by definition has a GWP value of one, methane is a live-fast, die-young greenhouse gas.

Methane traps very large quantities of heat in the first decade after it is released in to the atmosphere, but quickly breaks down.

After a decade, most emitted methane has reacted with ozone to form carbon dioxide and water. This carbon dioxide continues to heat the climate for hundreds or even thousands of years.

Emitting methane will always be worse than emitting the same quantity of carbon dioxide, no matter the time scale.

How much worse depends on the time period used to average out its effects. The most commonly used averaging period is 100 years, but this is not the only choice, and it is not wrong to choose another.

As a starting point, the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report from 2013 says methane heats the climate by 28 times more than carbon dioxide when averaged over 100 years and 84 times more when averaged over 20 years.

Many sources of methane

On top of these base rates of warming, there are other important considerations.

Fully considered using the 100-year GWP and including natural feedbacks, the IPCC’s report says fossil sources of methane – most of the gas burned for electricity or heat for industry and houses – can be up to 36 times worse than carbon dioxide. Methane from other sources – such as livestock and waste – can be up to 34 times worse.

Some cattle at a farm in New Zealand — Livestock are a source of methane emission into the atmosphere.
Flickr/mikeccross, CC BY-NC-ND

While some uncertainty remains, a well-regarded recent assessment suggested an upwards revision of fossil and other methane sources, that would increase their GWP values to around 40 and 38 times worse than carbon dioxide respectively.

These works will be assessed in the IPCC’s upcoming Sixth Assessment Report, with the physical science contribution due in 2021.

While we should prefer the most up to date science at any given time, the choice to consider – or not – the full impact of methane and the choice to consider its impact over 20, 100 or 500 years is ultimately political, not scientific.

Undervaluing or misrepresenting the impact of methane presents a clear risk for policy makers. It is vital they pay attention to the advice of scientists and bodies such as the IPCC.

Undervaluing methane’s impact in this way is not a risk for climate modellers because they rely on more direct assessments of the impact of gases than GWP.

Tipping points

The idea of climate tipping points is that, at some point, we may change the climate so much that it crosses an irreversible threshold.

At such a tipping point, the world would continue to heat well beyond our capability to limit the harm.

There are many tipping points we should be aware of. But exactly where these are – and precisely what the implications of crossing one would be – is uncertain.

Unfortunately, the only way we can be sure of where these tipping points are is to cross them. The only thing we know for sure about them is that the impact on lives, livelihoods and the places we love would be beyond catastrophic if we did.

But we cannot ignore disturbing impacts of climate change that are already here.

For example, damage to the landscape from the Black Summer bushfires may be irreversible and this represents its own form of climate tipping point.

The scientific understanding of climate change goes well beyond simple metrics like GWP. Shuffling between metrics – such as 20-year or 100-year GWP – cannot avoid the fact our very best chance of avoiding ever-worsening climate harm is to massively reduce our reliance on coal, oil and gas, along with reducing our emissions from all other sources of greenhouse gas.

If we do this, we offer ourselves the best chance of avoiding crossing thresholds we can never return from.

Zebedee Nicholls, PhD Researcher at the Climate & Energy College, University of Melbourne and Tim Baxter, Fellow – Melbourne Law School; Senior Researcher – Climate Council; Associate – Australian-German Climate and Energy College, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Emissions of methane – a greenhouse gas far more potent than carbon dioxide – are rising dangerously

Pep Canadell, CSIRO; Ann Stavert; Ben Poulter, NASA; Marielle Saunois, Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) – Université Paris-Saclay ; Paul Krummel, CSIRO, and Rob Jackson, Stanford University

Fossil fuels and agriculture are driving a dangerous acceleration in methane emissions, at a rate consistent with a 3-4℃ rise in global temperatures this century.

Our two papers published today provide a troubling report card on the global methane budget, and explore what it means for achieving the Paris Agreement target of limiting warming to well below 2℃.

Methane concentration in the atmosphere reached 1,875 parts per billion at the end of 2019 – more than two and a half times higher than pre-industrial levels.

Once emitted, methane stays in the atmosphere for about nine years – a far shorter period than carbon dioxide. However its global warming potential is 86 times higher than carbon dioxide when averaged over 20 years and 28 times higher over 100 years.

In Australia, methane emissions from fossil fuels are rising due to expansion of the natural gas industry, while agriculture emissions are falling.

Agriculture and fossil fuels are driving the rise in methane emissions.
EPA

Balancing the global methane budget

We produced a methane “budget” in which we tracked both methane sources and sinks. Methane sources include human activities such as agriculture and burning fossil fuels, as well as natural sources such as wetlands. Sinks refer to the destruction of methane in the atmosphere and soils.

Our data show methane emissions grew almost 10% from the decade of 2000-2006 to the most recent year of the study, 2017.

Atmospheric methane is increasing by around 12 parts per billion each year – a rate consistent with a scenario modelled by the Intergovernmental Panel on Climate Change under which Earth warms by 3-4℃ by 2100.

From 2008-2017, 60% of methane emissions were man-made. These include, in order of contribution:

agriculture and waste, particularly emissions from ruminant animals (livestock), manure, landfills, and rice farming
the production and use of fossil fuels, mainly from the oil and gas industry, followed by coal mining
biomass burning, from wood burning for heating, bushfires and burning biofuels.

2000 years of atmospheric methane concentrations. Observations taken from ice cores and atmosphere. Source: BoM/CSIRO/AAD.

The remaining emissions (40%) come from natural sources. In order of contribution, these include:

wetlands, mostly in tropical regions and cold parts of the planet such as Siberia and Canada
lakes and rivers
natural geological sources on land and oceans such as gas–oil seeps and mud volcanoes
smaller sources such as tiny termites in the savannas of Africa and Australia.

So what about the sinks? Some 90% of methane is ultimately destroyed, or oxidised, in the lower atmosphere when it reacts with hydroxyl radicals. The rest is destroyed in the higher atmosphere and in soils.

Increasing methane concentrations in the atmosphere could, in part, be due to a decreasing rate of methane destruction as well as rising emissions. However, our findings don’t suggest this is the case.

Measurements show that methane is accumulating in the atmosphere because human activity is producing it at a much faster rate than it’s being destroyed.

NASA video showing sources of global methane.

Source of the problem

The biggest contributors to the methane increase were regions at tropical latitudes, such as Brazil, South Asia and Southeast Asia, followed by those at the northern-mid latitude such as the US, Europe and China.

In Australia, agriculture is the biggest source of methane. Livestock are the predominant cause of emissions in this sector, which have declined slowly over time.

The fossil fuel industry is the next biggest contributor in Australia. Over the past six years, methane emissions from this sector have increased due to expansion of the natural gas industry, and associated “fugitive” emissions – those that escape or are released during gas production and transport.

Tropical emissions were dominated by increases in the agriculture and waste sector, whereas northern-mid latitude emissions came mostly from burning fossil fuels. When comparing global emissions in 2000-2006 to those in 2017, both agriculture and fossil fuels use contributed equally to the emissions growth.

Since 2000, coal mining has contributed most to rising methane emissions from the fossil fuel sector. But the natural gas industry’s rapid growth means its contribution is growing.

Some scientists fear global warming will cause carbon-rich permafrost (ground in the Arctic that is frozen year-round) to thaw, releasing large amounts of methane.

But in the northern high latitudes, we found no increase in methane emissions between the last two decades. There are several possible explanations for this. Improved ground, aerial and satellite surveys are needed to ensure emissions in this vast region are not being missed.

More surveys are needed into thawing permafrost in the high northern latitudes.
Pikist

Fixing our methane leaks

Around the world, considerable research and development efforts are seeking ways to reduce methane emissions. Methods to remove methane from the atmosphere are also being explored.

Europe shows what’s possible. There, our research shows methane emissions have declined over the past two decades – largely due to agriculture and waste policies which led to better managing of livestock, manure and landfill.

Livestock produce methane as part of their digestive process. Feed additives and supplements can reduce these emissions from ruminant livestock. There is also research taking place into selective breeding for low emissions livestock.

The extraction, processing and transport of fossil fuels contributes to substantial methane emissions. But “super-emitters” – oil and gas sites that release a large volume of methane – contribute disproportionately to the problem.

This skewed distribution presents opportunities. Technology is available that would enable super-emitters to significantly reduce emissions in a very cost effective way.

Clearly, current upward trends in methane emissions are incompatible with meeting the goals of the Paris climate agreement. But methane’s short lifetime in the atmosphere means any action taken today would bring results in just nine years. That provides a huge opportunity for rapid climate change mitigation.

Pep Canadell, Chief research scientist, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO; Ann Stavert, Project Scientist; Ben Poulter, Research scientist, NASA; Marielle Saunois, Enseignant-chercheur, Laboratoire des sciences du climat et de l’environnement (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) – Université Paris-Saclay ; Paul Krummel, Research Group Leader, CSIRO, and Rob Jackson, Chair, Department of Earth System Science, and Chair of the Global Carbon Project, globalcarbonproject.org, Stanford University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Turning methane into carbon dioxide could help us fight climate change

It’s not cows’ fault they fart, but the methane they produce is warming the planet.
Robert Bye/Unsplash

Pep Canadell, CSIRO and Rob Jackson, Stanford University

Discussions on how to address climate change have focused, very appropriately, on reducing greenhouse gas emissions, particularly those of carbon dioxide, the major contributor to climate change and a long-lived greenhouse gas. Reducing emissions should remain the paramount climate goal.

However, greenhouse gas emissions have been increasing now for two centuries. Damage to the atmosphere is already profound enough that reducing emissions alone won’t be enough to avoid effects like extreme weather and changing weather patterns.

In a paper published today in Nature Sustainability, we propose a new technique to clean the atmosphere of the second most powerful greenhouse gas people produce: methane. The technique could restore the concentration of methane to levels found before the Industrial Revolution, and in doing so, reduce global warming by one-sixth.

Our new technique sounds paradoxical at first: turning methane into carbon dioxide. It’s a concept at this stage, and won’t be cheap, but it would add to the tool kit needed to tackle climate change.

The methane menace

After carbon dioxide, methane is the second most important greenhouse gas leading to human-induced climate change. Methane packs a climate punch: it is 84 times more powerful than carbon dioxide in warming the planet over the first 20 years of its molecular life.

Methane emissions from human activities are now larger than all natural sources combined. Agriculture and energy production generate most of them, including emissions from cattle, rice paddies and oil and gas wells.

The result is methane concentrations in the atmosphere have increased by 150% from pre-industrial times, and continue to grow. Finding ways to reduce or remove methane will therefore have an outsize and fast-acting effect in the fight against climate change.

What we propose

The single biggest challenge for removing methane from the atmosphere is its low concentration, only about 2 parts per million. In contrast, carbon dioxide is now at 415 parts per million, roughly 200 times higher. Both gases are much more diluted in air than when found in the exhaust of a car or in a cow’s burp, and both would be better served by keeping them out of the atmosphere to start with.

Nonetheless, emissions continue. What if we could capture the methane after its release and convert it into something less damaging to climate?

That is why our paper proposes removing all methane in the atmosphere produced by human activities – by oxidising it to carbon dioxide. Such an approach has not been proposed before: previously, all removal techniques have only been applied to carbon dioxide.

This is the equivalent of turning 3.2 billion tonnes of methane into 8.2 billion tonnes of carbon dioxide (equivalent to several months of global emissions). The surprising aspect to this trade is that it would reduce global warming by 15%, because methane is so much more warming than carbon dioxide.

Proposed industrial array to oxidise methane to carbon dioxide.
Jackson et al. 2019 Nature Sustainability

This reaction yields energy rather than requires it. It does require a catalyst, though, such as a metal, that converts methane from the air and turns it into carbon dioxide.

One fit-for-purpose family of catalysts are zeolites. They are crystalline materials that consist of aluminum, silicon and oxygen, with a very porous molecular structure that can act as a sponge to soak up methane.

They are well known to industrial researchers trying to oxidise methane to methanol, a valuable chemical feedstock.

We envision arrays of electric fans powered by renewable energy to force large volumes of air into chambers, where the catalyst is exposed to air. The catalyst is then heated in oxygen to form and release CO₂. Such arrays of fans could be placed anywhere where renewable energy – and enough space – is available.

We calculate that with removal costs per tonne of CO₂ rising quickly from US$50 to US$500 or more this century, consistent with mitigation scenarios that keep global warming below 2℃, this technique could be economically feasible and even profitable.

We won’t know for sure, though, until future research highlights the precise chemistry and industrial infrastructure needed.

Beyond the clean-up we propose here, methane removal and atmospheric restoration could be an extra tool in humanity’s belt as we aim for stringent climate targets, while providing new economic opportunities.

Future research and development will determine the technical and economic feasibility of methane removal. Even if successful, methane- and other carbon-removal technologies are no substitute for strong and rapid emissions reductions if we are to avoid the worst impacts of global warming.

Pep Canadell, Chief research scientist, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO and Rob Jackson, Chair, Department of Earth System Science, and Chair of the Global Carbon Project, globalcarbonproject.org, Stanford University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

NZ introduces groundbreaking zero carbon bill, including targets for agricultural methane

Agriculture – including methane from cows and sheep – currently contributes almost half of New Zealand’s greenhouse emissions.
from http://www.shutterstock.com, CC BY-ND

Robert McLachlan, Massey University

New Zealand’s long-awaited zero carbon bill will create sweeping changes to the management of emissions, setting a global benchmark with ambitious reduction targets for all major greenhouse gases.

The bill includes two separate targets – one for the long-lived greenhouse gases carbon dioxide and nitrous oxide, and another target specifically for biogenic methane, produced by livestock and landfill waste.

Launching the bill, Prime Minister Jacinda Ardern said:

Carbon dioxide is the most important thing we need to tackle – that’s why we’ve taken a net zero carbon approach. Agriculture is incredibly important to New Zealand, but it also needs to be part of the solution. That is why we have listened to the science and also heard the industry and created a specific target for biogenic methane.

The Climate Change Response (Zero Carbon) Amendment Bill will:

Create a target of reducing all greenhouse gases, except biogenic methane, to net zero by 2050
Create a separate target to reduce emissions of biogenic methane by 10% by 2030, and 24-47% by 2050 (relative to 2017 levels)
Establish a new, independent climate commission to provide emissions budgets, expert advice, and monitoring to help keep successive governments on track
Require government to implement policies for climate change risk assessment, a national adaptation plan, and progress reporting on implementation of the plan.

Bringing in agriculture

Preparing the bill has been a lengthy process. The government was committed to working with its coalition partners and also with the opposition National Party, to ensure the bill’s long-term viability. A consultation process in 2018 yielded 15,000 submissions, more than 90% of which asked for an advisory, independent climate commission, provision for adapting to the effects of climate change and a target of net zero by 2050 for all gasses.

Throughout this period there has been discussion of the role and responsibility of agriculture, which contributes 48% of New Zealand’s total greenhouse gas emissions. This is an important issue not just for New Zealand and all agricultural nations, but for world food supply.

Another critical question involved forestry. Pathways to net zero involve planting a lot of trees, but this is a short-term solution with only partly understood consequences. Recently, the Parliamentary Commissioner for the Environment suggested an approach in which forestry could offset only agricultural, non-fossil emissions.

Now we know how the government has threaded its way between these difficult choices.

Separate targets for different gases

In signing the Paris Agreement, New Zealand agreed to hold the increase in the global average temperature to well below 2°C and to make efforts to limit it to 1.5°C. The bill is guided by the latest Intergovernmental Panel on Climate Change (IPCC) report, which details three pathways to limit warming to 1.5°C. All of them involve significant reductions in agricultural methane (by 23%-69% by 2050).

Farmers will be pleased with the “two baskets” approach, in which biogenic methane is treated differently from other gasses. But the bill does require total biogenic emissions to fall. They cannot be offset by planting trees. The climate commission, once established, and the minister will have to come up with policies that actually reduce emissions.

In the short term, that will likely involve decisions about livestock stocking rates: retiring the least profitable sheep and beef farms, and improving efficiency in the dairy industry with fewer animals but increased productivity on the remaining land. Longer term options include methane inhibitors, selective breeding, and a possible methane vaccine.

Ambitious net zero target

Net zero by 2050 on all other gasses, including offsetting by forestry, is still an ambitious target. New Zealand’s emissions rose sharply in 2017 and effective mechanisms to phase out fossil fuels are not yet in place. It is likely that with protests in Auckland over a local 10 cents a litre fuel tax – albeit brought in to fund public transport and not as a carbon tax per se – the government may be feeling they have to tread delicately here.

But the bill requires real action. The first carbon budget will cover 2022-2025. Work to strengthen New Zealand’s Emissions Trading Scheme is already underway and will likely involve a falling cap on emissions that will raise the carbon price, currently capped at NZ$25.

In initial reaction to the bill, the National Party welcomed all aspects of it except the 24-47% reduction target for methane, which they believe should have been left to the climate commission. Coalition partner New Zealand First is talking up their contribution and how they had the agriculture sector’s interests at heart.

While climate activist groups welcomed the bill, Greenpeace criticised the bill for not being legally enforceable and described the 10% cut in methane as “miserly”. The youth action group Generation Zero, one of the first to call for zero carbon legislation, is understandably delighted. Even so, they say the law does not match the urgency of the crisis. And it’s true that since the bill was first mooted, we have seen a stronger sense of urgency, from the Extinction Rebellion to Greta Thunberg to the UK parliament’s declaration of a climate emergency.

New Zealand’s bill is a pioneering effort to respond in detail to the 1.5ºC target and to base a national plan around the science reported by the IPCC.

Many other countries are in the process of setting and strengthening targets. Ireland’s Parliamentary Joint Committee on Climate recently recommended adopting a target of net zero for all gasses by 2050. Scotland will strengthen its target to net zero carbon dioxide and methane by 2040 and net zero all gasses by 2045. Less than a week after this announcement, the Scottish government dropped plans to cut air departure fees (currently £13 for short and £78 for long flights, and double for business class).

One country that has set a specific goals for agricultural methane is Uruguay, with a target of reducing emissions per kilogram of beef by 33%-46% by 2030. In the countries mentioned above, not so different from New Zealand, agriculture produces 35%, 23%, and 55% of emissions, respectively.

New Zealand has learned from processes that have worked elsewhere, notably the UK’s Climate Change Commission, which attempts to balance science, public involvement and the sovereignty of parliament. Perhaps our present experience in balancing the demands of different interest groups and economic sectors, with diverse mitigation opportunities and costs, can now help others.

Robert McLachlan, Professor in Applied Mathematics, Massey University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New Zealand’s zero carbon bill: much ado about methane

File 20180712 27039 1d1g807.jpg?ixlib=rb 1.1 — New Zealand is considering whether or not agricultural greenhouse gases should be considered as part of the country’s transition to a low-emission economy.
from http://www.shutterstock.com, CC BY-SA

Robert McLachlan, Massey University

New Zealand could become the first country in the world to put a price on greenhouse gas emissions from agriculture.

Leading up to the 2017 election, the now Prime Minister Jacinda Ardern famously described climate change as “my generation’s nuclear-free moment”. The promised zero carbon bill is now underway, but in an unusual move, many provisions been thrown open to the public in a consultation exercise led by Minister for Climate Change James Shaw.

More than 4,000 submissions have already been made, with a week still to go, and the crunch point is whether or not agriculture should be part of the country’s transition to a low-emission economy.

Zero carbon options

Many of the 16 questions in the consultation document concern the proposed climate change commission and how far its powers should extend. But the most contentious question refers to the definition of what “zero carbon” actually means.

The government has set a net zero carbon target for 2050, but in the consultation it is asking people to pick one of three options:

net zero carbon dioxide – reducing net carbon dioxide emissions to zero by 2050
net zero long-lived gases and stabilised short-lived gases – carbon dioxide and nitrous oxide to net zero by 2050, while stabilising methane
net zero emissions – net zero emissions across all greenhouse gases by 2050

The three main gases of concern are carbon dioxide (long-lived, and mostly produced by burning fossil fuels), nitrous oxide (also long-lived, and mostly produced by synthetic fertilisers and animal manures) and methane (short-lived, and mostly produced by burping cows and sheep). New Zealand’s emissions of these gases in 2016 were 34 million tonnes (Mt), 9Mt, and 34Mt of carbon dioxide equivalent (CO₂e), respectively.

All three options refer to “net” emissions, which means that emissions can be offset by land use changes, primarily carbon stored in trees. In option 1, only carbon dioxide is offset. In option 2, carbon dioxide and nitrous oxide are offset and methane is stabilised. In option 3, all greenhouses gases are offset.

Gathering support

Opposition leader Simon Bridges has declared his support for the establishment of a climate change commission. DairyNZ, an industry body, has appointed 15 dairy farmers as “climate change ambassadors” and has been running a nationwide series of workshops on the role of agricultural emissions.

Earlier this month, Ardern and the Farming Leaders Group (representing most large farming bodies) published a joint statement that the farming sector and the government are committed to working together to achieve net zero emissions from agri-food production by 2050. Not long after, the Climate Leaders Coalition, representing 60 large corporations, announced their support for strong action to reduce emissions and for the zero carbon bill.

However, the devil is in the detail. While option 2 involves stabilising methane emissions, for example, it does not specify at what level or how this would be determined. Former Green Party co-leader Jeanette Fitzsimons has argued that methane emissions need to be cut hard and fast, whereas farming groups would prefer to stabilise emissions at their present levels.

This would be a much less ambitious 2050 target than option 3, potentially leaving the full 34Mt of present methane emissions untouched. Under current international rules, this would amount to an overall reduction in emissions of about 50% on New Zealand’s 1990 levels and would likely be judged insufficient in terms of the Paris climate agreement. This may not be what people thought they were voting for in 2017.

Why we can’t ignore methane

To keep warming below 2℃ above pre-industrial global temperatures, CO₂ emissions will need to fall below zero (that is, into net removals) by the 2050s to 2070s, along with deep reductions of all other greenhouse gases. To stay close to 1.5℃, the more ambitious of the twin Paris goals, CO₂ emissions would need to reach net zero by the 2040s. If net removals cannot be achieved, global CO₂ emissions will need to reach zero sooner.

Therefore, global pressure to reduce agricultural emissions, especially from ruminants, is likely to increase. A recent study found that agriculture is responsible for 26% of human-caused greenhouse emissions, and that meat and dairy provide 18% of calories and 37% of protein, while producing 60% of agriculture’s greenhouse gases.

A new report by Massey University’s Ralph Sims for the UN Global Environment Facility concludes that currently, the global food supply system is not sustainable, and that present policies will not cut agricultural emissions sufficiently to limit global warming to 1.5℃ above pre-industrial levels.

Finding a way forward

Reducing agricultural emissions without reducing stock numbers significantly is difficult. Many options are being explored, from breeding low-emission animals and selecting low-emission feeds to housing animals off-pasture and methane inhibitors and vaccines.

But any of these will face a cost and it is unclear who should pay. Non-agricultural industries, including the fossil fuel sector, are already in New Zealand’s Emissions Trading Scheme (ETS) and would like agriculture to pay for emissions created on the farm. Agricultural industries argue that they should not pay until cost-effective mitigation options are available and their international competitors face a similar cost.

The government has come up with a compromise. Its coalition agreement states that if agriculture were to be included in the ETS, only 5% would enter into the scheme, initially. The amount of money involved here is small – NZ$40 million a year – in an industry with annual export earnings of NZ$20 billion. It would add about 0.17% to the price of whole milk powder and 0.5% to the wholesale price of beef.

However, it would set an important precedent. New Zealand would become the first country in the world to put a price agricultural emissions. Many people hope that the zero carbon bill will represent a turning point. It may even inspire other countries to follow suit.

Robert McLachlan, Professor in Applied Mathematics, Massey University

This article was originally published on The Conversation. Read the original article.

Why methane should be treated differently compared to long-lived greenhouse gases

File 20180607 137295 b7km0d.jpg?ixlib=rb 1.1 — Livestock is a significant source of methane, a potent but short-lived greenhouse gas.
from http://www.shutterstock.com, CC BY-SA

Dave Frame, Victoria University of Wellington; Adrian Henry Macey, Victoria University of Wellington, and Myles Allen, University of Oxford

New research provides a way out of a longstanding quandary in climate policy: how best to account for the warming effects of greenhouse gases that have different atmospheric lifetimes.

Carbon dioxide is a long-lived greenhouse gas, whereas methane is comparatively short-lived. Long-lived “stock pollutants” remain in the atmosphere for centuries, increasing in concentration as long as their emissions continue and causing more and more warming. Short-lived “flow pollutants” disappear much more rapidly. As long as their emissions remain constant, their concentration and warming effect remain roughly constant as well.

Our research demonstrates a better way to reflect how different greenhouse gases affect global temperatures over time.

Cost of pollution

The difference between stock and flow pollutants is shown in the figure below. Flow pollutant emissions, for example of methane, do not persist. Emissions in period one, and the same emissions in period two, lead to a constant (or roughly constant) amount of the pollutant in the atmosphere (or river, lake, or sea).

With stock pollutants, such as carbon dioxide, concentrations of the pollutant accumulate as emissions continue.

Flow and stock pollutants over time. In the first period, one unit of each pollutant is emitted, leading to one unit of concentration. After each period, the flow pollutant decays, while the stock pollutant remains in the environment.
provided by author, CC BY

The economic theory of pollution suggests different approaches to greenhouse gases with long or short lifetimes in the atmosphere. The social cost (the cost society ought to pay) of flow pollution is constant over time, because the next unit of pollution is just replacing the last, recently decayed unit. This justifies a constant price on flow pollutants.

In the case of stock pollutants, the social cost increases with constant emissions as concentrations of the pollutant rise, and as damages rise, too. This justifies a rising price on stock pollutants.

A brief history of greenhouse gas “equivalence”

In climate policy, we routinely encounter the idea of “CO₂-equivalence” between different sorts of gases, and many people treat it as accepted and unproblematic. Yet researchers have debated for decades about the adequacy of this approach. To summarise a long train of scientific papers and opinion pieces, there is no perfect or universal way to compare the effects of greenhouse gases with very different lifetimes.

This point was made in the first major climate report produced by the Intergovernmental Panel on Climate Change (IPCC) way back in 1990. Those early discussions were loaded with caveats: global warming potentials (GWP), which underpin the traditional practice of CO₂-equivalence, were introduced as “a simple approach … to illustrate the difficulties inherent in the concept”.

The problem with developing a concept is that people might use it. Worse, they might use it and ignore all the caveats that attended its development. This is, more or less, what happened with GWPs as used to create CO₂-equivalence.

The science caveats were there, and suggestions for alternatives or improvements have continued to appear in the literature. But policymakers needed something (or thought they did), and the international climate negotiations community grasped the first option that became available, although this has not been without challenges from some countries.

Better ways to compare stocks and flows

An explanation of the scientific issues, and how we address them, is contained in this article by Michelle Cain. The approach in our new paper shows that modifying the use of GWP to better account for the differences between short- and long-lived gases can better link emissions to warming.

Under current policies, stock and flow pollutants are treated as being equivalent and therefore interchangeable. This is a mistake, because if people make trade-offs between emissions reductions such that they allow stock pollutants to grow while reducing flow pollutants, they will ultimately leave a warmer world behind in the long term. Instead, we should develop policies that address methane and other flow pollutants in line with their effects.

Then the true impact of an emission on warming can be easily assessed. For countries with high methane emissions, for example from agriculture, this can make a huge difference to how their emissions are judged.

For a lot of countries, this issue is of secondary importance. But for some countries, particularly poor ones, it matters a lot. Countries with a relatively high share of methane in their emissions portfolios tend to be either middle-income countries with large agriculture sectors and high levels of renewables in their electricity mix (such as much of Latin America), or less developed countries where agricultural emissions dominate because their energy sector is small.

This is why we think the new research has some promise. We think we have a better way to conceive of multi-gas climate targets. This chimes with new possibilities in climate policy, because under the Paris Agreement countries are free to innovate in how they approach climate policy.

Improving the environmental integrity of climate policy

This could take several forms. For some countries, it may be that the new approach provides a better way of comparing different gases within a single-basket approach to greenhouse gases, as in an emissions trading scheme or taxation system. For others, it could be used to set separate but coherent emissions targets for long- and short-lived gases within a two-basket approach to climate policy. Either way, the new approach means countries can signal the centrality of carbon dioxide reductions in their policy mix, while limiting the warming effect of shorter-lived gases.

The new way of using global warming potentials demonstrably outperforms the traditional method in a range of emission scenarios, providing a much more accurate indication of how stock and flow pollutants affect global temperatures. This is especially so under climate mitigation scenarios.

Well designed policies would assist sectoral fairness within countries, too. Policies that reflect the different roles of stock and flow pollutants would give farmers and rice growers a more reasonable way to control their emissions and reduce their impact on the environment, while still acknowledging the primacy of carbon dioxide emissions in the climate change problem.

An ideal approach would be a policy that aimed for zero emissions of stock pollutants such as carbon dioxide and low but stable (or gently declining) emissions of flow pollutants such as methane. Achieving both goals would mean that a farm, or potentially a country, can do a better, clearer job of stopping its contribution to warming.

Dave Frame, Professor of Climate Change, Victoria University of Wellington; Adrian Henry Macey, Senior Associate, Institute for Governance and Policy Studies; Adjunct Professor, New Zealand Climate Change Research Institute. , Victoria University of Wellington, and Myles Allen, Professor of Geosystem Science, Leader of ECI Climate Research Programme, University of Oxford

This article was originally published on The Conversation. Read the original article.

Antarctic ice reveals that fossil fuel extraction leaks more methane than thought

File 20170823 13299 1u60k1n — The analysis of large amounts of ice from Antarctica’s Taylor Valley has helped scientists to tease apart the natural and human-made sources of the potent greenhouse gas methane.
Hinrich Schaefer, CC BY-ND

Hinrich Schaefer, National Institute of Water and Atmospheric

The fossil fuel industry is a larger contributor to atmospheric methane levels than previously thought, according to our research which shows that natural seepage of this potent greenhouse gas from oil and gas reservoirs is more modest than had been assumed.

In our research, published in Nature today, our international team studied Antarctic ice dating back to the last time the planet warmed rapidly, roughly 11,000 years ago.

Katja Riedel and Hinrich Schaefer discuss NIWA’s ice coring work at Taylor Glacier in Antarctica.

We found that natural seepage of methane from oil and gas fields is much lower than anticipated, implying that leakage caused by fossil fuel extraction has a larger role in today’s emissions of this greenhouse gas.

However, we also found that vast stores of methane in permafrost and undersea gas hydrates did not release large amounts of their contents during the rapid warming at the end of the most recent ice age, relieving fears of a catastrophic methane release in response to the current warming.

The ice is processed in a large melter before samples are shipped back to New Zealand.
Hinrich Schaefer, CC BY-ND

A greenhouse gas history

Methane levels started to increase with the industrial revolution and are now 2.5 times higher than they ever were naturally. They have caused one-third of the observed increase in global average temperatures relative to pre-industrial times.

If we are to reduce methane emissions, we need to understand where it comes from. Quantifying different sources is notoriously tricky, but it is especially hard when natural and human-driven emissions happen at the same time, through similar processes.

The most important of these cases is natural methane seepage from oil and gas fields, also known as geologic emissions, which often occurs alongside leakage from production wells and pipelines.

The total is reasonably well known, but where is the split between natural and industrial?

To make matters worse, human-caused climate change could destabilise permafrost or ice-like sediments called gas hydrates (or clathrates), both of which have the potential to release more methane than any human activity and reinforce climate change. This scenario has been hypothesised for past warming events (the “clathrate gun”) and for future runaway climate change (the so-called “Arctic methane bomb”). But how likely are these events?

Antarctic ice traps tiny bubbles of air, which represents a sample of ancient atmospheres.
Hinrich Schaefer, CC BY-ND

The time capsule

To find answers, we needed a time capsule. This is provided by tiny air bubbles enclosed in polar ice, which preserve ancient atmospheres. By using radiocarbon (14C) dating to determine the age of methane from the end of the last ice age, we can work out how much methane comes from contemporary processes, like wetland production, and how much is from previously stored methane. During the time the methane is stored in permafrost, sediments or gas fields, the 14C decays away so that these sources emit methane that is radiocarbon-free.

In the absence of strong environmental change and industrial fossil fuel production, all radiocarbon-free methane in samples from, say, 12,000 years ago will be from geologic emissions. From that baseline, we can then see if additional radiocarbon-free methane is released from permafrost or hydrates during rapid warming, which occurred around 11,500 years ago while methane levels shot up.

Tracking methane in ice

The problem is that there is not much air in an ice sample, very little methane in that air, and a tiny fraction of that methane contains a radiocarbon (14C) atom. There is no hope of doing the measurements on traditional ice cores.

Our team therefore went to Taylor Glacier, in the Dry Valleys of Antarctica. Here, topography, glacier flow and wind force ancient ice layers to the surface. This provides virtually unlimited sample material that spans the end of the last ice age.

A tonne of ice yielded only a drop of methane.
Hinrich Schaefer, CC BY-ND

For a single measurement, we drilled a tonne of ice (equivalent to a cube with one-metre sides) and melted it in the field to liberate the enclosed air. From the gas-tight melter, the air was transferred to vacuum flasks and shipped to New Zealand. In the laboratory, we extracted the pure methane out of these 100-litre air samples, to obtain a volume the size of a water drop.

Only every trillionth of the methane molecules contains a 14C atom. Our collaborators in Australia were able to measure exactly how big that minute fraction is in each sample and if it changed during the studied period.

Low seepage, no gun, no bomb

Because radiocarbon decays at a known rate, the amount of 14C gives a radiocarbon age. In all our samples the radiocarbon date was consistent with the sample age.

Radiocarbon-free methane emissions did not increase the radiocarbon age. They must have been very low in pre-industrial times, even during a rapid warming event. The latter indicates that there was no clathrate gun or Arctic methane bomb going off.

So, while today’s conditions differ from the ice-covered world 12,000 years ago, our findings implicate that permafrost and gas hydrates are not too likely to release large amounts of methane in future warming. That is good news.

Wetlands must have been responsible for the increase in methane at the end of the ice age. They have a lesser capacity for emissions than the immense permafrost and clathrate stores.

Geologic emissions are likely to be lower today than in the ice age, partly because we have since drained shallow gas fields that are most prone to natural seepage. Yet, our highest estimates are only about half of the lower margin estimated for today. The total assessment (natural plus industrial) for fossil-fuel methane emissions has recently been increased.

In addition, we now find that a larger part of that must come from industrial activities, raising the latter to one third of all methane sources globally. For comparison, the last IPCC report put them at 17%.

Measurements in modern air suggest that the rise in methane levels over the last years is dominated by agricultural emissions, which must therefore be mitigated. Our new research shows that the impact of fossil fuel use on the historic methane rise is larger than assumed. In order to mitigate climate change, methane emissions from oil, gas and coal production must be cut sharply.

Hinrich Schaefer, Research Scientist Trace Gases, National Institute of Water and Atmospheric

This article was originally published on The Conversation. Read the original article.

Capturing the true wealth of Australia’s waste

File 20170823 13308 ce4edu — Methane is produced in landfill when organic waste decomposes.
Shutterstock

William Clarke, The University of Queensland and Bernadette McCabe, University of Southern Queensland

One of the byproducts of landfill is “landfill gas”, a mixture of mostly methane and carbon dioxide generated by decomposing organic material. Methane is a particularly potent greenhouse gas, but it can be captured from landfill and used to generate clean electricity.

Methane capture is a valuable source of power but, more importantly, it can significantly reduce Australia’s methane emissions. However the opportunity to produce energy from waste is largely being squandered, as up to 80% of the potential methane in waste is not used.

If more councils were prepared to invest in better facilities, Australians would benefit from less waste in landfill and more energy in our grids. Even the by-product from using state-of-art processing methods can be used as a bio-fertiliser.

And while these facilities are initially more expensive, Australians are generally very willing to recycle, compost and take advantage of community schemes to reduce waste. It’s reasonable to assume that a considerable percentage of our population would support updating landfill plants to reduce methane emissions.

Recycling in Australia

Australia may have a bad rap when it comes to waste recycling, but there are plenty of positives.

Australians produce approximately 600 kilograms of domestic waste per person, per year – no more than most northern European countries, which set the benchmark in sustainable waste management.

Looking at kerbside bins we, on average, recycle 30-35% of that waste, saving much of our paper, glass, aluminium and steel from landfill (which also saves and reduces emissions).

Although the household recycling rate in Australia is less than the best-performing EU recycling rates of 40-45%, this is primarily due to a lack of access to (or awareness of) schemes to recycle e-waste and metals. Data therefore suggests that at the community level, there is a willingness to minimise and recycle waste.

Campaigns urging us to ‘care more’ about food waste miss the point

Between 55% and 60% of kerbside waste sent to landfill in Australia is organic material. Over 65% of this organic fraction is food waste, similar to the make-up of the EU organic waste stream, comprised of 68% of food waste.

Despite this large fraction, approximately half of the household organic we produce – mostly garden waste – is separately collected and disposed, again demonstrating high participation by the community in recycling when collection and disposal options are available.

Turning waste into energy

Energy recovery from waste is the conversion of non-recyclable material into useable heat, electricity, or fuel. Solid inorganic waste can be converted to energy by combustion, but organic waste like kitchen and and garden refuse has too much moisture to be treated this way.

Instead, when organic waste is sent to landfill it is broken down naturally by microorganisms. This process releases methane, a greenhouse gas 25 times more potent than carbon dioxide.

Around 130 landfills in Australia are capturing methane and using it to generate electricity. Based on installed power generation capacity and the amount of waste received, Australia’s largest landfills use 20-30% of the potential methane in waste for electricity generation.

Ravenhall in Melbourne processes 1.4 million tonnes of waste per year, and proposes to generate 8.8 megawatts (MW) of electricity by 2020. Roughly 461,000 tonnes of waste goes to Woodlawn in NSW, and in 2011 it generated 4MW of electrical power. Swanbank in Queensland receives 500,000 tonnes a year and generates 1.1MW.

The remainder of the methane is flared due to poor gas quality or insufficient transmission infrastructure, is oxidised as it migrates towards the surface of the landfill, or simply escapes. The methane generating capacity of waste is also diminished because organics begin composting as soon as they reach landfill.

But there are more efficient ways to capture methane using specialised anaerobic digestion tanks. The process is simple: an anaerobic (oxygen free) tank is filled with organic waste, which is broken down by bacteria to produce biogas. This is similar to the natural process that occurs in landfill, but is much more controlled and efficient in a tank.

The biogas can be combusted to produce electricity and heat, or can be converted to pure biomethane to be used either in the mains gas grid, or as a renewable transport fuel. In contrast to landfills, 60-80% of the methane potential of waste is used to generate electricity in anaerobic digesters, with most of the remainder used to power waste handling and the digestion process.

The nutrient-rich sludge that remains after anaerobic digestion, called digestate, is also a valuable biofertiliser. It can support food production, and further reduce greenhouse gases by decreasing our reliance on energy-intensive manufactured fertilisers.

The use of food waste as a feedstock for anaerobic digestion is largely untapped in Australia but has huge potential. A site in Sydney’s geographic centre (Earth Power Technologies) and Richgro’s Jandakot facility near Perth are part of a handful that are converting food waste to energy using this technology.

The future of organic recycling

Local council recycling and waste infrastructure is typically not a priority election issue, except for those close to existing or proposed landfills.

Ratepayers are generally not informed of the possibility of separately collecting food waste, either for industrial-scale composting or methane capture. We have the right to this information, with costs and benefits presented in the context of the costs we already pay for waste management, and relative to the environmental performance of landfill.

As an example, landfill operators often promote the number of homes they power by electricity generated from methane as a key measure of sustainability. But how does this compare to the electricity and heat that might be obtained from an anaerobic digester that processes the same waste?

Given the choice, the Australian community may have an appetite to extend organic recycling beyond well-established garden waste composting. They only have to be asked.

William Clarke, Professor of waste management, The University of Queensland and Bernadette McCabe, Associate Professor and Principal Scientist, University of Southern Queensland

This article was originally published on The Conversation. Read the original article.

Wait, trees emit methane?

So where exactly is the treethane coming from?

Discovering methane-eating bacteria

A trillion trees to combat climate change

Share this:

Like this:

From underwater sediment to the atmosphere

Significant global contribution

The alarming human impact

So how do we reduce methane emissions?

Share this:

Like this:

Comparing apples and oranges

Limits of metrics

Many sources of methane

Tipping points

Share this:

Like this:

Balancing the global methane budget

Source of the problem

Fixing our methane leaks

Share this:

Like this:

The methane menace

What we propose

Share this:

Like this:

Bringing in agriculture

Separate targets for different gases

Ambitious net zero target

Share this:

Like this:

Zero carbon options

Gathering support

Why we can’t ignore methane

Finding a way forward

Share this:

Like this:

Cost of pollution

A brief history of greenhouse gas “equivalence”

Better ways to compare stocks and flows

Improving the environmental integrity of climate policy

Share this:

Like this:

A greenhouse gas history

The time capsule

Tracking methane in ice

Low seepage, no gun, no bomb

Share this:

Like this:

Recycling in Australia

Turning waste into energy

The future of organic recycling

Share this:

Like this: