Scientists and environmentalists have long been aware that the reforestation of degraded land offers an effective, large-scale method for removing carbon dioxide from the atmosphere and storing it in biomass and soils.
But how much would it cost to get even more people to reforest? A recent paper in Nature Climate Change works out what potential carbon prices could mean for carbon sequestration through reforestation and reduced deforestation. It then runs the numbers up against other methods scientists are currently using to reduce our carbon footprint, such as negative-emissions technologies (NETs).
The study was carried out by researchers at the San Francisco–based Earth Innovation Institute together with colleagues from The Nature Conservancy and the University of Wisconsin.
“We tried to come up with a general relationship for how people who make decisions about land use respond to the offer of money – whether they are more likely to plant trees or crops based on the market signals they’re getting,” said Jonah Busch, the paper’s lead author.
There is already a lot of data related to that question, he said. “As market prices for different crops go up and down, we can see people making decisions – forest being cleared or replanted or allowed to stand in response to that variation in crop prices.”
The researchers consulted three different data sets, including satellite data of global forest cover in 90 tropical and subtropical countries in 2000 and in 2010, then used a dynamic land cover change model to document non-forested lands being converted to forests through both natural regrowth and plantations.
“We simulate the effect of payments for increased carbon removals on future land-cover changes, accounting for site characteristics including slope, elevation, distance from cities, protected status, initial forest cover, agricultural revenue potential, continent and biome,” the paper states.
Under a business-as-usual scenario, 387.8 million hectares of land will be reforested between 2020 and 2050, according to the researchers’ projections, and remove 102.5 gigatons – more than 100 billion tons – of carbon dioxide from the atmosphere.
But a carbon price of USD 20 per ton would incentivize land users to increase reforestation during the same time period by more than 8 percent, upping the total by 31.8 million hectares to 419.6 million hectares. That increase corresponds to removing an extra 5.7 gigatons of carbon dioxide from the air. The price would also reduce deforestation by just over 13 percent, reducing emissions by another 21.5 percent, or 55 gigatons of carbon dioxide.
A carbon price of USD 50 per ton, meanwhile, would increase reforestation by 21.7 percent, or 84 million hectares, and reduce deforestation by 27.6 percent, or almost 150 million hectares. That amount of reforestation would remove 15 gigatons of carbon dioxide, while the reduced emissions from deforestation would be more than 108 gigatons.
While the prices are hypothetical, said Busch, the USD 20-a-ton calculation is based on current carbon market rates in Europe and in California, while USD 50 to 100 a ton would remove amounts of carbon dioxide consistent with the goals of the Paris Agreement.
A cheap yet effective solution
The modeling curves showed that the benefits start small and increase over time. They also allowed the researchers to compare abatement costs of reforestation to other methods such as bio-energy with carbon capture and storage (BECCS) and direct air carbon capture and storage (DACCS). “Most of those exist only on paper or in the lab,” said Busch. “There are some exceptions, but that’s basically it, while trees have been taking out carbon for millions of years. We have lots of data and experience on reforestation to look at.”
While cost is not the only consideration, it is an important one, he said. “We show that [restoration] is cost-effective relative to many other climate solutions.” And, he added, many previous studies have shown that, aside from climate mitigation, there are a lot of co-benefits to restoration, such as providing livelihoods, clean water and habitat for different species.
For Busch, the take-away from the Earth Innovation Institute study is clear: countries should be doing more reforestation, and more funding should be made available to pay for it.
“If you have a choice between two ways to fight climate change,” he said, “you want to be able to do the one that’s cheap and can do a lot, as opposed to one that’s expensive and can’t do very much.”