Rubbish in, rubbish out: China university study finds methane emissions hole in climate change models
- Cutting the amount of municipal waste going into landfill could help achieve global targets, but it needs to be done ‘rapidly’
- About 90 per cent of emissions from the sector could be eliminated by 2050 with existing technologies, the researchers said
Reducing the amount of waste going into landfill is vital if a cut in methane emissions is to be achieved, and about 90 per cent of the solid waste industry’s contribution could be eliminated by 2050 with existing technology, the researchers said.
“No global analysis has considered the warming that could be averted through improved solid waste management,” they said.
Co-author Kok Sin Woon, associate professor at Xiamen University Malaysia’s school of energy and chemical engineering, told the South China Morning Post that the global adoption of mitigation strategies will require abrupt “technical and behavioural changes”.
How will China, largest emitter of methane globally, reduce emissions?
“We found that it would be necessary to accelerate the complete adoption of mitigation strategies by at least 9 to 17 years – 2033 to 2041 – to be on track with the progress to achieve the Global Methane Pledge,” he said.
The pledge, spearheaded by the US and European Union in 2021, aims to cut global methane emissions to 30 per cent below 2020 levels by 2030. Signatories represent 45 per cent of the world’s methane emissions.
China, which together with the US produces the most municipal solid waste, has not signed the pledge but has released a methane reduction action plan ahead of the COP28 summit. More than 50 per cent of China’s municipal solid waste currently ends up in landfills.
Woon said complete adoption of mitigation strategies to curb emissions from solid waste would also help to achieve the Paris Agreement goal of keeping warming to below 2 degrees. Without action, the world is on course to reach 2.6 degrees by 2100.
In an editor’s summary of the paper in Science, Senior Editor H. Jesse Smith noted that “methane emissions from solid waste sites provide a considerable fraction of the global methane budget and are an important target for reductions”.
China issues action plan to cut methane emissions ahead of COP28 climate summit
The researchers estimated that municipal solid waste-related emissions will increase by up to 2.8 per cent each year, potentially reaching 3.33 gigatonnes of annual global waste generation by 2050 – double that of 2016.
But if the Paris target is to be met, the world’s maximum cumulative budget for methane emissions must not exceed 27 gigatonnes of carbon dioxide warming equivalents, according to the team’s modelling.
By converting the estimated solid waste methane emissions into carbon dioxide warming equivalents, they calculated that the world will exceed its 1.5 degree budget by 2028 and will surpass the 2 degree mark by 2044 under business-as-usual conditions.
According to the paper, methane’s short atmospheric lifespan of about a decade means that cutting its emissions could greatly reduce short-term global warming through “rapid decarbonisation”.
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Methane accounts for about one-third of global warming and its lifespan of 10 years in the atmosphere – compared to carbon dioxide’s 120 years – means its reduction can rapidly restrict warming, according to an article on the study published by Science in its Perspective section.
The team also investigated mitigation strategies and identified four ways of dealing with municipal solid waste that could help the world to achieve the goals of the methane pledge and the Paris agreement – if they are adopted rapidly, the paper said.
According to the researchers, the most effective strategy would be anaerobic digestion – which uses bacteria to break down organic matter – and could reduce cumulative emissions by 70 per cent, relative to business-as-usual levels.
The team found that by simply halving municipal solid waste generation at source, countries would achieve a 63 per cent cut in methane emissions. Diverting organic materials for composting could drive a 57 per cent reduction, the researchers said.
Finally, the study assessed the effectiveness of retrofitting landfills with tools for biogas capture, a strategy that could yield a fall in cumulative emissions of 27 per cent.
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The researchers said anaerobic digestion was theoretically the most effective strategy for low to upper-middle income countries, which produce larger amounts of biodegradable waste.
But they also noted that building anaerobic digesters could be both technologically and financially unfeasible for lower income nations, suggesting halving waste generation at source should remain a priority for these countries, the paper said.
High income nations should also aim to halve their waste generation, as these countries tend to generate more non-biodegradable waste through their greater use of disposable packaging, the researchers said.
But they stressed that a combination of strategies was necessary to meet methane reduction goals, especially since cutting municipal waste by half would require drastic behavioural changes that could be challenging to achieve.
The adoption of retrofitted landfills and organics composting, combined with a 50 per cent drop in the amount of waste generated could result in a municipal waste system with “net-zero warming”, the paper said.
According to Woon, more advanced awareness and education in high income countries will make it easier to introduce the behavioural changes needed to reduce waste generation.
Some of these nations also “already have better access to advanced technologies” like anaerobic digesters, he added.
“We cannot rely on a single waste facility to dispose of/treat the waste. Hence, the mitigation strategies consist of a combination of varying waste facilities to cater for different waste types,” Woon said.
