To win the race against catastrophic climate change, we need to go carbon-negative now

By Joanna D. Underwood

As the UN secretary-general António Guterres stated at the COP24 climate meeting in Poland, countries must quickly set and achieve much more ambitious goals to keep global warming below catastrophic levels.  Even if they met their current emissions reduction pledges under the Paris agreement, it still wouldn’t be enough to keep warming under the critical threshold of 1.5 or 2 degrees Celsius.

In the run-up to COP24, a spate of dire climate reports trumpeted the extreme urgency of climate action. The Intergovernmental Panel on Climate Change and others warned the window is closing to prevent catastrophic warming, with just 12 years left to change our trajectory.  We are not on pace to keep warming below 1.5 or 2 degrees, past which we can expect massive sea level rise, floods, fires, droughts, disruptions in food production, species extinctions, etc.

To avoid that, making the emissions reduction math work requires subtraction. We can’t just slow the rate at which we add greenhouse gases to the atmosphere. We must also accelerate ways to effectively remove greenhouse gases from the atmosphere, using what are called “carbon-negative” strategies.

Just before COP24 an Australian consortium issued the “Perth Protocol” calling for a “truly carbon-negative” approach “that removes, sequesters, stores and binds greenhouse gas already in the atmosphere.” Such strategies were touted at previous COP climate meetings, though mostly in a futuristic way – something to look forward to in decades to come. There are various carbon-negative demonstration projects in the pipeline, some of which were featured at COP24. But they are many years away from large-scale deployment, and we need to deploy carbon-negative energy on a large scale starting now.

There is one powerful carbon-negative energy strategy deployable and scalable today: renewable natural gas (RNG). Although it’s natural gas, it’s not a fossil fuel. It’s derived from the methane biogases emitted by decomposing organic wastes such as food waste, farm waste and municipal wastewater. These wastes are ubiquitous in urban and rural environments alike.

Here’s why RNG is carbon-negative: If organic wastes are left to decompose on farm fields, in landfills or elsewhere, the methane biogases they generate are mostly released into the atmosphere, where they act as powerful greenhouse gases. But if organic wastes are collected and processed in tanks called anaerobic digesters, these potent, methane-rich biogases don’t escape. Instead, they are captured and refined into RNG.

Chemically RNG is nearly identical to “geologic” natural gas (the ordinary, fossil fuel kind), but it’s the lowest-carbon fuel available today. It burns as cleanly as fossil natural gas, and can be used in the same pipelines, engines, power plants, etc. But producing RNG has none of the negative climate impacts of fossil fuel extraction.  A byproduct of making RNG in anaerobic digesters is “biosolids” which can be used as high-quality fertilizer, replacing chemical fertilizers and the GHG emissions related to them, on top of the emissions saved by capturing the biogases.

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