Emissions of carbon to the atmosphere must remain below ∼250 petagrams (PgC) (918 PgCO2) from 2021 onward to achieve the Paris Agreement’s goal of limiting global temperature rise to well below 2 °C. At present rates, that amount of carbon will be emitted by 2045. It follows that even necessary and drastic cuts in emissions (i.e., a rapid transition from fossil fuels to renewable energy sources) must be accompanied by carbon dioxide removal (CDR) or negative emissions strategies.
As per a recent study published in Proceedings of the National Academy of Sciences (PNAS), carbon storage capacity in forests across the globe is only at 88% of its potential. The study sets out to help prioritize locations for increasing reserves.
The findings of the paper ‘The global potential for increased storage of carbon on land’ could assist the design of strategies to combat climate change, say researchers from the U S based Woodwell Climate Research Center, as forest systems act like sponges, sequestering carbon dioxide from the atmosphere. Improved management of existing forests, such as conserving native tree species and prohibiting logging, could help realize nearly three quarters of this unmet potential, the majority of which (71%) lies in the tropics, according to the study.
Constraining the climate crisis requires urgent action to reduce anthropogenic emissions while simultaneously removing carbon dioxide from the atmosphere. Improved information about the maximum magnitude and spatial distribution of opportunities for additional land-based removals of CO2 is needed to guide on-the-ground decision-making about where to implement climate change mitigation strategies.
This study presents a globally consistent spatial dataset (approximately 500-m resolution) of current, potential, and unrealized potential carbon storage in woody plant biomass and soil organic matter. Among the top ten countries with the greatest potential are Brazil— second only to Russia—Indonesia, Democratic Republic of Congo, India, and Mexico.
"The size of the untapped reservoir—the space on land that is available for additional carbon storage—is considerable: about 287 petagrams (PgC) after we set aside land that is critical to food production and human habitation," the study suggests. A petagram (PgC) is equivalent to one billion tons.
Most (78%) of this unrealized potential is found in woody biomass, while 22% is in soil, according to the study, which combined existing data, field measurements and geospatial imagery to assess the gap between current and potential carbon storage.
To meet the objectives of the Paris Agreement, to prevent the average temperature increase from exceeding 2°C compared to pre-industrial levels, global emissions must remain below 250 PgC. At current rates, that amount would be reached by 2045, the study says.
In this context, researchers say it is essential to understand carbon storage capacity in order to advance so-called "nature-based" climate solutions, such as forest maintenance, improved management of degraded ecosystems, and restoration—planting trees where native forests have been felled.
The findings reflect the high rates of historic deforestation and forest degradation in the tropics. "Generally speaking, countries with greater forest loss have larger land-carbon deficits and greater unrealized potential for additional carbon storage," says Walker the main author.
In Brazil, restoration accounts for less than 10% of potential climate benefits (related to carbon storage), according to the study. It says the greatest gains will come from focusing efforts where forest cover has been at least partially maintained.
While additional research is needed to understand the impact of natural disturbances and biophysical feedbacks, the study projects that the potential for additional carbon storage in woody biomass will increase (+17%) by 2050 despite projected decreases (−12%) in the tropics.
The study results establish an absolute reference point and conceptual framework for national and jurisdictional prioritization of locations and actions to increase land-based carbon storage. It also provides a framework for prioritizing actions related to the restoration, management, and maintenance of woody carbon stocks and associated soils.
Despite increased interest in land-based carbon storage as a climate solution, there are physical limits on how much additional carbon can be incorporated into terrestrial ecosystems. To effectively determine where and how to act, jurisdictions need robust data illustrating the magnitude and distribution of opportunities to increase carbon storage, as well as information on the actions available to achieve that storage.
Here, this study provides globally consistent maps for directing additional carbon storage under current and future climate, as well as a framework for determining how that storage could be gained through restoration, improved management, or maintenance of woody biomass and soil organic matter. The estimates provide an upper bound on how improved land stewardship can mitigate the climate crisis.
The study results strengthen the growing body of research devoted to quantifying the potential for natural climate solutions to mitigate climate change by providing critical limits on the potential for land-based carbon storage and elucidating the most relevant actions for storing additional carbon.
While reducing fossil fuel emissions is of paramount importance, increasing carbon storage in land-based reservoirs provides a significant opportunity to remove additional carbon from the atmosphere. The study estimates an untapped global land carbon reservoir of approximately 286.7 PgC after safeguarding areas critical to food production and human habitation.
Climate change impacts could diminish the magnitude of this maintenance and management opportunity by as much as 38% by 2050, with further reductions possible due to changes in human and/or natural disturbance regimes (e.g., increasing deforestation/ degradation and/or fire frequency/ intensity), reinforcing the need for rigorous data-driven planning and prioritization informed by expert knowledge of conditions on the ground.
The full paper can be accessed here