Drone shot of mangrove trees off the coast of the Yucatán Peninsula in Mexico. Carlos Aguilera / EDF Mexico
The world needs nature-based climate solutions (NbCS). These approaches use conservation, restoration, and management of natural and agricultural systems to retain existing, and sequester additional, carbon while reducing emissions of CO2 and other greenhouse gases. NbCS have been suggested to meet 20-30% of the world’s climate goals. Correspondingly, nature-based actions are included in the national commitments of 63% (104 of 168) of the signatories of the Paris Agreement.
However, defining the climate impact of different solutions requires accurate scientific measurement and accounting of greenhouse gas mitigation, including how long that benefit lasts. Where we lack accurate measurements and estimates of future durability, we cannot yet rely on NbCS to meet our climate goals.
Assessment of the science on NbCS
Environmental Defense Fund recently worked with experts in academia and other conservation and research institutions to assess the scientific confidence in more than 40 NbCS that have been proposed. The results of that inquiry are both optimistic and sobering.
The four most frequently credited NbCS by the four major carbon credit registries have high scientific confidence – tropical and temperate forest avoided conversion or degradation and reforestation. The confidence of the scientific community in those NbCS supports investing in these as climate solutions and demonstrates that we can develop sufficient understanding of process, measurement, and accounting methods necessary to meet high quality crediting requirements.
However, the experts concluded that 90% (39/42) of the proposed NbCS assessed in the study currently have insufficient scientific evidence for having climate impact we can count on. Within that 90% are NbCS like avoided conversion and degradation of systems as different as mangroves and boreal forests (see below for why).
Promisingly, the experts do have confidence that we can remedy this situation: focused research over the next five years could resolve many of the remaining questions for two-thirds of those pathways. Given that some, like agroforestry, tropical peatland conservation, and biochar additions are also estimated to have large-scale climate impacts, this study provides a roadmap for prioritizing research efforts.
The importance of location
Every NbCS is different, and so are the specific uncertainties and research needs. Prediction of how natural systems may change as the climate changes – affecting their carbon storage and greenhouse gas emissions – is inherently uncertain. We are better at modeling some systems (like tropical forests) than others (like seagrass beds). But all NbCS pathways have something in common – location matters.
The climate impact may be dependent on the local environment (including everything from soil type to the present and future temperature and rainfall levels), site management history (has the land use changed and how has it been managed?), and local social conditions (what do local communities need and value from the system?).
That dependence may explain why estimated climate impact of specific NbCS vary so widely – leading to uncertainty. If we can identify the combinations of elements that lead to carbon storage versus methane loss in coastal systems and peatlands, for example, we may be able to resolve a lot of the uncertainty. So, a well-designed, systematic research and modeling approach should help us make rapid progress on the climate front.
There is no time to lose to initiate this research if we are to realize the needed contribution of nature to meet net zero goals.
Below we highlight two examples of NbCS we assessed, mangroves and boreal forests, and explain the importance of location.
Mangroves
The sources of uncertainty around avoided conversion of mangroves provide a good example of the importance of location. Healthy mangrove systems are very productive. Over time, they create deep, organic soils that support both their growth and provide habitat and food for a myriad of other species. They also trap a lot of soil washing to the sea, further building soil carbon stocks.
One is tempted to assume that all NbCS involving mangroves are, therefore, beneficial climate solutions. But some mangrove forests also release substantial amounts of methane, which can counteract the climate benefit of the carbon they are sequestering. In those systems, poor water quality appears to stimulate methane production. Additionally, in some regions the mangroves themselves are likely to disappear under the rising sea. As a result, some mangroves will be a good bet to conserve as a durable climate solution. But some will not, and we need to be able to distinguish between the two. Geography and management (ensuring that water quality is also protected, if necessary) matter.
Boreal forests
The boreal region – by some accounting, the largest terrestrial biome on earth – provides another example of how the durability of carbon storage relies on predictions of future climate, adding a layer of uncertainty.
Several NbCS pathways are in the boreal region. While we tend to discuss boreal forests or peatlands as if they are subject to uniform pressures and environmental changes, from Russia to Canada to Finland, the evidence suggests very different climate mitigation potential depending on the location. Boreal systems on the western sides of continents are predicted to become hotter and drier relative to those on the eastern edges as global climate changes. As a result, both reduced moisture and increased probability of wildfires will threaten western boreal systems, making the carbon stores in those regions less durable and increasing the rates of methane release. So, we need to dig in, define the opportunities and risks, and outline where they fall on the map to build confidence in boreal solutions overall.
Conclusion
There is no time to lose to initiate this research if we are to realize the needed contribution of nature to meet net zero goals. Identifying and mapping patterns that explain why and where the variation in effective climate mitigation potential exists – particularly as the climate changes – would significantly improve our ability to strategically target effective NbCS actions.
Building on the scientific foundations in our report, we need to also include social constraints (for example, the ability to maintain high water quality in mangrove areas or reduce the probability and need for land conversion to higher intensity uses) to increase our understanding of, and confidence in, NbCS opportunities worldwide. This work would result in spatially-explicit identification of high quality, low risk climate solutions that would guide investment and confident climate mitigation. As a result, additional NbCS would join tropical and temperate forest interventions as scientifically substantiated pathways to impact. Other NbCS might need more specific research on measurement methods or baseline establishment. Collectively, this research should be prioritized so we can accelerate implementation of scientifically founded and effective NbCS action across the globe.
For more on this study, read the blogs:
- How to act fast and smart (and where to move more cautiously) on NbCS.
- Time to double down on high-confidence nature investments for climate and resilience.
- It’s Time to Uncover the Mysteries of Blue Carbon.