Nick Carne
Paying land users to replant tropical forests rather than cut them down could play an increasingly important role in reducing atmospheric carbon dioxide, US researchers say.
Their modelling suggests that providing monetary incentives to plant trees would be more cost-effective than carbon capture and storage in some countries, though still less so than soil carbon sequestration and enhanced weathering techniques.
A team led by Jonah Busch from the Earth Innovation Institute in San Francisco created spatially disaggregated marginal abatement cost (MAC) curves for tropical reforestation by simulating the effects of payments for carbon dioxide removals on land-cover change in 90 countries.
They estimate that removals from tropical reforestation between 2020 and 2050 could be increased by 5.6% at a carbon price of US$20 a tonne of CO2 or 14.8% at $50 a tonne. {%recommended 7937%}
Overall, avoiding deforestation offers 7.2 to 9.6 times as much potential low-cost abatement as reforestation, they say, but reforestation at $20 a tonne offers more potential in 21 countries, 17 of which are in Africa.
Ten countries comprise 55% of potential low-cost abatement from tropical reforestation.
Busch and colleagues’ analysis took account of specific site characteristics such as slope, elevation, distance from cities, protected status, initial forest cover, agricultural revenue potential, continent and biome.
“Our estimates represent economic potentials subject to the modelling assumption that land users would be as responsive to changes in carbon prices as they were to historical variation in agricultural prices; these estimates do not account for economic, social, legal or technical hurdles associated with operationalising carbon price incentives under specific policies,” they write in the journal Nature.
The potential of reforestation has been widely recognised, but until now it has been difficult to put numbers on the likely impact because generating MAC curves for encouraging trees to grow is more challenging than for simply refraining from cutting any more down – for three reasons.
First the researchers say, historical reforestation is harder to observe because it happens gradually. Second, accounting for the trajectory of CO2 removal (that is, sequestration) over time is more complicated because it is subject to reversals due to harvest or natural losses. And third, different types of forest growth have different carbon removal trajectories.
Newly available data allowed them to overcome these challenges, but there are still more to deal with in translating knowledge into action
Reforestation programs, they note, “are constrained by economic, social, legal and technical challenges and sensitivity to biological diversity safeguards”.
Nevertheless, individual countries have included more than 120 million hectares of reforestation in their national climate pledges, with forest-based mitigation comprising one-quarter of planned emission reductions.
And rapid advances in the ability to monitor the impact of reforestation, the researchers add, could further advance the use of carbon price incentives for reforestation.
