Jesse Reynolds, LEGAL PLANET
Unfortunately, a new scientific paper overstates forests’ potential
Today, The Guardian reports:
Tree planting ‘has mind-blowing potential’ to tackle climate crisis
Planting billions of trees across the world is by far the biggest and cheapest way to tackle the climate crisis, according to scientists…
As trees grow, they absorb and store the carbon dioxide emissions that are driving global heating. New research estimates that a worldwide planting programme could remove two-thirds of all the emissions that have been pumped into the atmosphere by human activities, a figure the scientists describe as “mind-blowing”.
global tree restoration potential
Global tree restoration potential
And the underlying scientific paper, published in Science, makes an unambiguous claim:
ecosystem restoration [is] the most effective solution at our disposal to mitigate climate change.
[See also the press release from ETH Zurich.]
That is, the authors claim that reforestation is more effective than reducing greenhouse gas emissions.
Unfortunately, this is misleading, if not false, as well as potentially dangerous. It is misleading for several reasons.
– The authors do not define “effective.” Many policies and actions that could achieve a single given objective are impossible or undesirable.
– They do not consider cost. Planting trees requires arable land, physical and natural resources, and labor, all of which could be used for other valuable purposes. The most recent assessment report from the Intergovernmental Panel on Climate Change (IPCC) gave a range of $20 to $100 per ton of removed carbon dioxide (CO2), [PDF, p. 851]; which is roughly the same costs as many means of reducing greenhouse gas emissions that are presently under discussion.
– The authors do not consider how such reforestation might come about. This land — roughly the size of the US, including Alaska — is owned and managed by many private persons, companies, nongovernmental organizations, and governments. How these numerous diverse actors could be incentivized or somehow forced to undertake expensive reforestation efforts is important unclear.
They do not consider the rate of carbon removal. The IPCC gives a high-end estimate of 14 billion tons CO2 per year [PDF, p. 851], whereas humans’ emissions are about 40 billion tons per year. Thus, at this generous rate, reforestation could only compensate for a third of current emissions, with not impact on accumulated atmospheric carbon dioxide. Furthermore, the amount of removal suggested by the new paper would require about 55 years.
– The authors simply assume that all potentially forested land “outside cropland and urban
regions” would be “restored to the status of existing forests.” People use land for purposes other than crops and cities. For example, humans’ largest use of land — agricultural or otherwise — is rangeland for livestock. Thus, the paper implicitly assumes a dramatic reduction in meat consumption or intensification of meat production.
– They reach a remarkably high estimate of carbon removal per area. This paper indirectly says that 835 tons CO2 could be removed per hectare (that is, 10,000 square meters), whereas the IPCC report on Land Use, Land-Use Change, and Forestry reaches values from 1.5 to 30 tons per hectare.
– In a critique, Pros. Mark Maslin and Simon Lewis say “The authors have forgotten the carbon that’s already stored in the vegetation and soil of degraded land that their new forests would replace. The amount of carbon that reforestation could lock up is the difference between the two.”
– The paper does not address the (im)permanence of trees, which could later be cut down.
A recent investigation by a reporter at Propublica concluded:
In case after case, I found that carbon credits [for reforestation] hadn’t offset the amount of pollution they were supposed to, or they had brought gains that were quickly reversed or that couldn’t be accurately measured to begin with. Ultimately, the polluters got a guilt-free pass to keep emitting CO₂, but the forest preservation that was supposed to balance the ledger either never came or didn’t last.
Ultimately, if cost, feasibility, and speed were no matter, then one simply could claim that permanently ending the use of fossil fuels tomorrow is the most effective. This statement would be true, but largely irrelevant.