An international team of scientists is warning that relying on nature to remove planet-warming emissions will fail to halt global warming.
The study, released Monday in the peer-reviewed journal Nature, used climate models to measure the flux of carbon dioxide released by humanity and absorbed by the world’s oceans and land.
The results showed that under the best-case scenario, natural carbon sinks could remove half of the roughly 40 billion tonnes currently emitted by human activities, said Kirsten Zickfeld, a climate scientist at Simon Fraser University (SFU) and co-author of the study.
“We’re still cutting down trees and old-growth forests, draining wetlands and peatlands, destroying mangroves — all these carbon sinks. We need to protect them,” said the SFU professor.
“But by doing so, we can’t rely on them as a fossil fuel offset.”
On the road to stabilizing the global climate, Zickfeld said natural carbon sinks need to be counted separately from emissions from fossil fuels — set aside to help draw down greenhouse gases already in the atmosphere and deep ocean.
Bad accounting
Every year, countries around the world submit inventories showing how much carbon is released and how much is absorbed within their national borders.
That means counting emissions produced by entire economies — including from transportation, buildings and the fossil fuel industry — while at the same time, subtracting carbon dioxide sucked up in forests that are deemed “managed” by people.
Current reporting rules mean countries are taking credit for at least some of the 20 billion tonnes of carbon sucked up by natural carbon sinks. In so doing, the study found governments are overcounting emission reductions from managed natural areas.
The work brought together leading climate researchers from Europe and Australia, as well as from leading research institutions like the University of Oxford in the United Kingdom and the Massachusetts Institute of Technology in the United States.
Co-author Nathan Gillet, a federal research scientist at the Canadian Centre for Climate Modelling and Analysis, said many of his colleagues were the first to develop the concept of “net zero” — the point at which humans stop increasing the amount of greenhouse gases in the atmosphere.
In the past 15 years, the net zero concept has been adopted across the world as a target to mitigate the worst effects of climate change. To achieve a net zero equilibrium, countries and corporations have proposed dropping carbon emissions — through fuel switching, electrification or increased energy efficiency — or drawing down atmospheric CO2 through natural carbon sinks or mechanical removal.
However, countries taking credit for some of the CO2 removed by nature is throwing off global calculations to hit net zero emissions by mid-century, and has set the global economy on a path that will fail to stabilize the planet’s average temperatures, added Gillet.
“Under those conditions, we would still expect some additional warming,” said the Victoria-based researcher.
Risk of abuse growing
At a global level, it’s not clear how much carbon is being improperly counted under current emission inventory rules, said Zickfeld. But the authors warn the potential for abuse is massive.
If all-natural absorption of carbon was counted as human-caused, it could offset half of global emissions. At that scale, taking credit for natural carbon sinks would allow anyone to declare they had achieved net zero without reducing active emissions at all, the study says.
In their call for transparency, the authors warn that rising political and economic pressures to reduce CO2 emissions will likely provide incentives for governments to re-classify land as “managed.”
That, they add, could lead coastal or island states to take credit for the natural absorption of carbon into the oceans of their exclusive economic zones.
Canada criticized for double counting natural carbon sinks
In Canada, where about 60 per cent of forests are considered managed, governments and the forestry sector have been repeatedly criticized for failing to revamp their calculations to avoid taking credit for forests regenerated after wildfires.
A March 2023 audit from Canada’s Commissioner of the Environment and Sustainable Development found the federal government had failed to properly account for emissions from the country’s forestry sector.
Among several recommendations, commissioner Jerry DeMarco said the federal government “did not provide a clear and complete picture” of greenhouse gases from forestry and called for an independent expert review to assess any gaps.
DeMarco has since called out Ottawa for failing to follow through on his office’s recommendations.
And in September, Nature Canada released a report that concluded net logging emissions hit 147 megatonnes in 2022. That would make the industry the third-highest emitting sector of the Canadian economy, with only the oil and gas sector’s 217 megatonnes and the transport sector’s 156 megatonnes reaching larger totals.
Michael Polanyi, a policy and campaign manager for Nature Canada, told Glacier Media earlier this month that by not counting emissions from wildfires and allowing the forestry industry to take credit from tree regrowth after, Canada is masking emissions from logging and leaving a “gaping hole in its climate plan.”
Canada has one of the worst track records when it comes to double counting natural carbon sinks, said Andrew Weaver, a climate scientist at the University of Victoria and another co-author of the paper.
“They’re seeking ways to take credit for regrowing forests,” he said. “It’s completely outrageous.”
A problem of scale
Both Gillet and Zickfeld said preserving natural areas clearly matters if Canada and other countries hope to meet their targets to preserve biodiversity. But for Weaver, the central problem comes down to scale.
While fossil fuels take millions of years to form underground, forests tend to grow and mature within hundreds of years. Throughout that time, trees remain vulnerable to releasing carbon back into the atmosphere in a single wildfire season. Zickfeld pointed to 2023 when huge tracts of Canada’s biosphere went up in flames amid the country’s most destructive wildfire season on record.
“The argument here is that we can’t plant trees and get credit for capturing carbon that took tens of millions of years to store. It doesn’t work that way,” said Weaver, who previously served as leader of the BC Green Party. “Net zero requires geological storage.”
To stop planetary warming, Weaver said countries need to store CO2 underground — not in trees, swamps and grasslands, and certainly not in the atmosphere.
He said right now, the cheapest way to do that is to avoid bringing gas or oil to the surface in the first place. Another option, said the UVic researcher, is to vastly expand direct air capture technologies to suck carbon out of the air and bury it in geologic deposits — something critics say is wildly expensive and unrealistic.
“I reject arguments that suggest planting trees will make a difference. The issue is really quite simple: we’re combusting ancient fossils and we’re not drawing that down,” said Weaver. “Everything else is a delay.”
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