Meeting the goal set out in the Paris agreement of limiting global warming to well below 1.5–2 degrees Celcius will require efforts that go far beyond reducing greenhouse gas emissions, argue Jackson and colleagues in a new commentary published on 20 May in Nature Sustainability (1). The authors propose a somewhat counterintuitive approach of converting methane (CH4) to carbon dioxide (CO2) in the atmosphere, which they suggest could yield cost-effective benefits over time.
Rising greenhouse gas emissions and increasing global temperature are making it more and more difficult to meet the targets set out in the Paris agreement. After several years of stable CO2 levels, CO2 emissions reached a record 37 billion tonnes in 2018. Moreover, concentrations of CH4 — the second most atmosphere-polluting anthropogenic greenhouse gas — surpassed 1,860 ppb for the first time in 2018, and are now two-and-a-half times higher than preindustrial levels, the authors write.
Moreover, methane is 84 times more potent than CO2 over the first 20 years after release and around 28 times more potent after a century, and react with nitrogen oxides leading to ozone pollution, according to the authors. The main sources of CH4 emissions are agricultural livestock and burning fossil fuels. In fact, around 60 per cent of methane is generated by humans.
Nonetheless, most approaches to reducing greenhouse gas concentrations focus on removing CO2. But require hundreds of billions of tons to be removed from the atmosphere over decades. And even then and under various scenarios, do not reduce greenhouse gas concentrations to pre-industrial levels. Whereas, methane concentrations are much lower —yet more potent — and could, therefore, be reduced to pre-industrial levels by removing just 3 billion tonnes of the gas from the atmosphere.
The authors believe removing and converting methane to CO2 could reduce warming in the short-term, allowing more time to adapt to warming from long-lived greenhouse gases such as CO2 and nitrous oxide (N2O). If methane is trapped gas and oxidized to CO2, the process could add the equivalent of a few months of current industrial CO2 emissions, but would also eliminate around one-sixth of total radiative forcing.
However, capturing methane is difficult because concentrations in the atmosphere are so low. To achieve this, the researchers have identified catalysts that can absorb methane and other gases. One promising candidate, zeolite, is a crystalline material mainly consists of aluminium, silicon, and oxygen that essentially acts like a sponge owing to its porous molecular structure and relatively large surface area.
At the moment, the idea is only in the conceptual stage, but if effectively implemented could potentially convert one harmful greenhouse gas into another that is much less potent. Moreover, each tonne of methane removed from the atmosphere would be worth more than $12,000 or almost €11,000, based on current assessment models. That means, an array of catalysts the size of a football pitch could potentially generate millions in revenue.
Owing to the potential environmental and monetary benefits, the authors propose the creation of a “new initiative to assess the feasibility of large-scale methane conversion and, ultimately, atmospheric restoration”.
(1) Jackson, R.B. et al. Methane removal and atmospheric restoration. Nature (2019). DOI: 10.1038/s41893-019-0299-x