Boosting natural systems to mitigate climate change
All 1.5°C global warming scenarios call for carbon removal. Natural systems provide the most readily available mechanisms, so how can these be boosted to the levels required?
Environment — Global
According to the Intergovernmental Panel on Climate Change, to limit global warming to 1.5°C by 2100 we need to:
- strongly reduce global net anthropogenic CO2 emissions by 2030 and reach net zero around 2050
- deeply reduce agricultural emissions
- deploy at large scale afforestation, bioenergy, and carbon removal technologies
The more we delay reduction in CO2 emissions, the more we will need carbon removals after 2050 to return warming to 1.5°C. Engineered approaches to carbon removal remain expensive and it is currently hard to fully understand the potential trade-offs with other ecosystem services. While continued research and development in engineered approaches is needed, “natural” approaches are often perceived as:
- easier and faster to implement
- good for other objectives such as biodiversity, clean air and water, and adaptation to climate change
Through photosynthesis and respiration, terrestrial ecosystems currently remove more carbon than they emit, leading to a net sink at the global scale. However, in some regions, recent climate change has already shifted ecosystems to being net emitters of carbon. We need to rapidly reduce emissions from all sectors to avoid large temperature increases that could undermine the ability of natural ecosystems to absorb more carbon than they release, thus reinforcing climate change. The destruction of natural ecosystems to meet human demand has led to large emissions: it is estimated that deforestation and peatland drainage contribute to about 15% of total global greenhouse gas emissions, while also reducing the area where carbon can be naturally sequestered in the future.
Protecting and restoring ecosystems
Preventing agricultural expansion to carbon-rich natural ecosystems is key to mitigating climate change. Reducing or limiting human consumption of agricultural commodities can prevent or slow down agricultural expansion. Limiting the consumption of animal-based products is often highlighted as a game-changer, since it is currently estimated that a third of global cropland is used to feed livestock, while ruminant livestock also emits methane. For instance, the EAT-Lancet Commission recommends to not eat more than two meat portions per week.
The example of Brazil shows that a reduction in deforestation can be achieved without necessarily reducing agricultural production, when combined with productivity gains. Annual deforestation in the Brazilian Amazon fell by about 75% between 2004 and 2009, while still enabling agricultural exports to grow. Several measures proved to be highly effective at curbing deforestation during that period:
- new protected areas and indigenous reserves at the deforestation frontier
- a robust satellite-based system for real-time detection of deforestation
- confiscation of equipment and/or livestock in illegally deforested areas
- restrictions to access rural credit in municipalities with high rates of illegal deforestation
Ecosystem restoration is the other critical lever for removing carbon from the atmosphere. Trees sequester carbon as they are growing, and (almost) all land cover types can be targeted for planting trees:
- forests can be restored and reforested
- burnt and abandoned agricultural land can be afforested
- perennial crops, trees planted in combination with annual crops or pasture, and/or green infrastructure can spread across agricultural land
- parks, green roofs, or urban orchards can expand in cities
Despite its small territory and high population density, Rwanda has become a restoration leader. It has pledged to restore two-thirds of its total land area by 2030 and reverse a long forest loss trend due to conflict, pastureland expansion, and overexploitation of forest products to supply urban areas. Forest gain over the last decade has been possible through an ambitious National Forest Policy that set clear targets, and the promotion of land sharing with the establishment of tree plantations throughout agricultural land uses.
Co-benefits v trade-offs
Increasing carbon sequestration in soils has lower potential than protecting and restoring ecosystems for climate mitigation. However, it does offer co-benefits in terms of the increased long-term profitability and higher resilience of agriculture activities. Deep-root grass and moderate grazing, either through controlled livestock density or better grazing timing, can improve soil carbon in grasslands. Low-till or no-till practices, planting cover crops or double crops instead of leaving fields fallow, or applying compost or crop residues to fields can increase soil carbon in cropland. However, soil carbon sequestration benefits are highly context specific, as they depend on how far soils currently are from their saturation point. The adoption of regenerative agriculture practices is expected to lead to the largest carbon sequestration in currently depleted soils. For instance, grazing of relatively unmanaged rangelands has been identified as a strong driver of soil organic carbon loss, and large carbon sequestration benefits could be achieved in the rangelands of Argentina, southern Africa, and Australia.
Despite the potential for large co-benefits, there are significant risks that large-scale deployment of nature-based climate solutions will also create trade-offs. For instance, it is estimated that about half of the pledged reforestation is set to become mono-species commercial plantations that will be harvested after 10 to 20 years maximum. This will lead to lower carbon benefits than keeping existing forests, and potentially negative outcomes on water and biodiversity. In some countries, it leads to land grabs by governments and private investors. On the agricultural side, farmers must manage a complex system where the change in practices can take several years to master, to avoid unintended consequences. These can result in, for instance, higher pesticide, herbicide, or water use, and lower yields of the main cash crops due to labour shortages. High up-front costs and delayed benefits might also discourage economic actors to invest in these natural solutions.
Long vision, action now
A long-term vision of public and private decision-makers is necessary to boost carbon removals from nature. We urgently need in each country:
- quantifiable targets for ecosystems conservation, restoration, and soil carbon sequestration, in policy documents
- a holistic, inclusive land-use plan that can secure carbon-rich ecosystems and sequestered carbon, and enhance synergies with other objectives
- land and carbon monitoring systems, especially in carbon and biodiversity-rich ecosystems and in areas targeted for carbon sequestration
- economic incentives and products that can reduce the risk of economic actors who invest in natural carbon removals
- extensive research and knowledge capitalisation from field experiments on potential solutions for natural carbon removals
- wide dissemination of this knowledge to policymakers, economic actors, and young generations