The effectiveness of global protected areas for climate change mitigation

Article https://doi.org/10.1038/s41467-023-38073-9 The effectiveness of global protected areas for climate change mitigation Received: 6 December 2022 Accepted: 14 April 2023 L. Duncanson 1 , M. Liang1, V. Leitold1, J. Armston1, S. M. Krishna Moorthy1, R. Dubayah 1, S. Costedoat 2, B. J. Enquist3,4, L. Fatoyinbo 5, S. J. Goetz 6, M. Gonzalez-Roglich7, C. Merow 8, P. R. Roehrdanz 2, K. Tabor 5,9 & A. Zvoleff2 Forests play a critical role in stabilizing Earth’s climate. Establishing protected areas (PAs) represents one approach to forest conservation, but PAs were rarely created to mitigate climate change. The global impact of PAs on the carbon cycle has not previously been quantified due to a lack of accurate global-scale carbon stock maps. Here we used ~412 million lidar samples from NASA’s GEDI mission to estimate a total PA aboveground carbon (C) stock of 61.43 Gt (+/− 0.31), 26% of all mapped terrestrial woody C. Of this total, 9.65 + /− 0.88 Gt of additional carbon was attributed to PA status. These higher C stocks are primarily from avoided emissions from deforestation and degradation in PAs compared to unprotected forests. This total is roughly equivalent to one year of annual global fossil fuel emissions. These results underscore the importance of conservation of high biomass forests for avoiding carbon emissions and preserving future sequestration. 1234567890():,; 1234567890():,; Check for updates Earth’s ecosystems play a critical role in the carbon cycle, with estimates of global terrestrial aboveground carbon (AGC) of ~308 Gt in 20101,2 and annual uptake of ~8 Gt CO23. The primary causes of AGC loss are deforestation and forest degradation, while vegetation carbon sinks are associated with afforestation and forest recovery. Several policy frameworks emphasize that habitat conservation and restoration should contribute simultaneously to biodiversity conservation and climate change mitigation4. These frameworks include the UN Sustainable Development Goals (SDGs), decisions under the United Nations Framework Convention on Climate Change (UNFCCC) and the Convention on Biological Diversity (CBD). To support goal setting and the implementation of international strategies and action plans, guidance is needed to identify how well-protected areas contribute to maximizing synergies between conserving biodiversity and other ecosystem services such as climate change mitigation5. Forest conservation is a crucial mechanism for forest management toward climate change mitigation, and for curbing biodiversity loss6,7. Protected areas are a foundation for global forest conservation efforts and monitoring PA effectiveness is key for determining progress in achieving the UN SDGs8. While most efforts to establish PAs have been focused on biodiversity protection9, there are clear co-benefits of biodiversity and carbon conservation efforts, as older, biodiverse forests also typically store more carbon5,6,10. PAs have been demonstrated to effectively avoid forest cover loss in many regions11–13, as well as regulate temperature and local climate14, and potentially boost carbon sequestration capacity15,16. Therefore, PA expansion may be a pathway to bolster climate change mitigation17. Intact forests, especially tropical forests, can sequester twice as much carbon than more humanimpacted forests and planted monocultures16,18. Protected forest areas are thought to contribute a large fraction (~27%) of the net global GHG sink3 but large uncertainties remain in the magnitudes of AGC stocks 1 Department of Geographical Sciences, University of Maryland, College Park, MD, USA. 2Moore Center for Science, Conservation International, Arlington, VA 22202, USA. 3Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA. 4The Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA. 5NASA Goddard Space Flight Center, Greenbelt, MD, USA. 6School of Informatics, Computing and Cyber Systems, Northern Arizona University, Flagstaff, AZ, USA. 7WCS, General Roca, Río Negro, Argentina. 8Eversource Energy Center and Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, USA. 9Department of Geography and Environmental Systems, University of Maryland Baltimore County, e-mail: Baltimore, MD, USA. Nature Communications | (2023)14:2908 1 Article and fluxes in terrestrial ecosystems19,20. As a result, the degree to which protected status contributes to avoided carbon emissions or enhanced sequestration at a global scale remains highly uncertain. Here, we analyze millions of spaceborne lidar-derived estimates of AGC from NASA’s Global Ecosystem Dynamics Investigation (GEDI21) to spatially quantify the carbon effectiveness of PAs and test the assumption that these areas provide disproportionately more ecosystem services through carbon storage and sequestration than nonprotected areas22. Previous attempts to quantify carbon content in PAs had high uncertainties and/or biases, as past satellite biomass products are known to saturate in high biomass forests23, such as old-growth PAs. GEDI is the first satellite lidar system designed specifically to map forest structure, and provides orders of magnitude more 3D samples of Earth’s forests than have previously been available, capable of collecting accurate data in even the densest and tallest forests23. GEDI launched on December 5, 2018, and is collecting full-waveform lidar samples from the International Space Station (ISS) between ~52°N and 52°S under the ISS orbit (Fig. 1). GEDI has three lasers operating at 1064 nm, each illuminated ~25 m circular “footprints” (circular pixels) to produce billions of high-resolution samples of surface elevation, vegetation height, and foliage distribution. GEDI is not a mapping mission, in that it does not collect data continuously over Earth’s surface, but instead provides samples spaced ~60 m apart along each laser track, with ~600-m spacing between tracks. Therefore not every area of every PA is mapped. 25 m samples are aggregated to 1 km estimates of Aboveground Biomass Density (AGBD, which is subsequently converted to AGCD)24. At the time of writing, GEDI has collected sufficient data to fill ~70% of all GEDI-domain 1 km pixels. GEDI collects data from the International Space Station (ISS), which covers all tropical and temperate forests, as well as the southern boreal, but does not collect data north of ~52° latitude. Thus, while the results in this paper are global scale, they are not truly global as they omit PAs north of ~52°. GEDI provides a richer dataset to quantitatively address questions of forest C stocks and fluxes than have been previously available. We use GEDI’s data to quantify the additional AGC stocks attributed to the existence of PAs (termed “carbon effectiveness” of PAs) at a global scale (within the GEDI domain). This is achieved through matching each PA to ecologically similar unprotected areas, or counterfactuals (based (...truncated)