Tree planting, peatland protection, and better land use could deliver 37% of the greenhouse gas reductions humanity must achieve by 2030, according to a study this week in the Proceedings of the National Academy of Sciences.

“Better stewardship of the land could have a bigger role in fighting climate change than previously thought,” concluded an international research team led by The Nature Conservancy. “If we are serious about climate change, then we are going to have to get serious about investing in nature,” said CEO Mark Tercek.

“Fortunately, this research shows we have a huge opportunity to reshape our food and land use systems,” added Unilever CEO Paul Polman.

The researchers costed some of the mitigation measures they studied at $10 per tonne of carbon dioxide averted, while costlier measures up to $100 per tonne would still be cost-effective by 2030. “Combined, the suggested ‘regreening of the planet’ would be equivalent to halting all burning of oil worldwide,” The Guardian reports. “Overall, better management of nature could avert 11.3 billion tonnes of carbon dioxide emissions a year by 2030, the study said, equivalent to China’s current carbon dioxide emissions from fossil fuel use. “

The study appears alongside warnings that sudden jumps in forest and soil emissions could be triggered by a warming world, adding up to what InsideClimate News calls a “spiraling global warming feedback”. After the last El Niño set off a record increase in global CO2 levels, NASA satellite data traced the result to “three massive tropical forest regions, in different parts of the world, that each responded to the rising temperatures in a very different way,” ICN reports.

“In the Amazon, El Niño clobbered photosynthesis,” said climate researcher Scott Denning at Colorado State University, as the rainforest stopped inhaling CO2 due to drought. In Africa’s tropical jungles and forests, “stuff just rotted faster” and drove up emissions, in response to record warmth and rain. In Indonesia, the hot, dry conditions led to epic forest and peat fires that released equally epic volumes of carbon dioxide and methane.

“Up to now, land ecosystems, mainly forests, have been mitigating part of the fossil fuel problem. They’ve been sucking CO2 out of air, about 25% of our fossil fuel emissions,” Denning told ICN. “The worry is that, as the climate warms, that will stop, and that’s exactly what we saw.” 

Earlier this month, meanwhile, the Washington Post reported on a 26-year study in a Massachusetts forest that documented carbon release from warming soils. “The study is one of the longest if not the longest climate change ecosystem experiment, beyond the one we are running in our own planet,” said Australian carbon cycle specialist Pep Canadell, who was not involved with the project.

“Starting in 1991, a team of researchers have been studying the same 18 plots of forest soil in the Harvard Forest in Massachusetts,” the Post explained. “Six of the plots are entirely undisturbed, representing the natural state of the forest floor; six are artificially heated through underground cables to 5°C degrees Celsius (9°F) above the normal temperature; and six are ‘disturbed,’ meaning that they contain heating cables, but the cables are not actually powered, so the temperature is not altered.” The hypothesis was that “warmer temperatures would lead microorganisms in the soil to become more active in breaking down plant matter and other materials. These microbes would then release more soil carbon into the atmosphere in the form of carbon dioxide gas.”

The latest results, reported in the journal Science, show 17% carbon loss from the top layer of heated soil.

“This magnitude of loss could amount to hundreds of petagrams—billions of metric tons—of carbon fluxing from the world’s forest soils to the atmosphere, if those soils responded to warming like the Harvard forest soils have done over the experimental period,” said scientist Jerry Melillo of the Marine Biological Laboratory in Woods Hole, MA, who has overseen the research from the beginning.

“I think everyone agrees that we don’t include the microbial feedback mechanisms very well in climate models,” he added. The Post covers some of the subtleties the researchers uncovered as to the way the carbon is actually released.

The overall focus on carbon, forests, and soils has Fast Company arguing for cities to treat trees as public health infrastructure, citing a separate Nature Conservancy report.

“Planting trees is an incredibly cheap and simple way to improve the well-being of people in a city,” the online digest argues. “A novel idea: Public health institutions should be financing urban greenery to support well-being and air quality.”

A 2016 study in California by the U.S. Forest Service concluded that trees deliver $5.82 in public benefits for every dollar spent planting them, Fast Company notes. “Because urban trees are often slotted into the ‘luxury’ or ‘nice to have’ category in city budgeting decisions—certainly less prioritized than public safety and infrastructure maintenance—funding is often inadequate, and fails to treat trees as a long-term investment.” That gap is reflected in municipal budgets that typically allocated about 0.3% of total spending to urban greenery.

“It’s not enough to just talk about why trees are important for health,” said lead author Rob McDonald. “We have to start talking about the systemic reasons why it’s so difficult for these sectors to interact—how the urban forestry sector can start talking to the health sector, and how we can create financial linkages between the two.”