Nature-based solutions (NbS) provide a glimmer of hope in an otherwise alarming IPCC climate report assessing the globe’s land and water ecosystems, which concludes that at least 30% of Earth’s surface must be protected so that ecosystem services can help curb warming.
NbS include the protection, enhancement, and restoration of natural systems that sequester carbon, improve resilience to climate impacts, and enhance biodiversity and ecosystem health while simultaneously contributing to UN Sustainable Development Goals (SDGs) for human populations, the IPCC report states.
Done right, NbS could contribute to climate change mitigation and resilience, with ecological and socio-economic co-benefits that include species and hydrologic protection, employment, food security, and equity.
But nature-based solutions are no substitute for emissions reductions, warn the authors. Increased climate impacts could overwhelm the benefits of NbS. Further, poorly-planned and -managed solutions could be ineffectual, or even do more harm than good. It is essential for local and Indigenous populations to participate in planning and managing NbS, to ensure supportive, adaptive management grounded in local knowledge, states the report.
The IPCC concludes that “~30% of Earth’s surface needs to be effectively conserved to maintain biodiversity and ecosystem services.” That means protecting the world’s remaining natural ecosystems is essential and urgent.
To this end, reforestation of formerly forested land “can help to protect and recover biodiversity and can be one of the most practical and cost-effective ways of sequestering and storing carbon.” But climate change makes forests increasingly vulnerable to disturbances such as pests, wildfires, and droughts, the authors warn. They find that these risks are reduced through ecological restoration, using diverse native species rather than creating monoculture plantations.
On the other hand, planting forests in areas not naturally forested—like savannahs and many temperate peatlands—can increase climate vulnerability, the report states. While protecting existing peatlands is a priority, artificial drainage and trees should be removed.
In urban areas, NbS includes tree canopy, green space and natural areas, wetland restoration, and sustainable stormwater management that reduces runoff and maximizes infiltration using rain gardens, infiltration trenches, and swales.
The report touts agroecological farming as “a holistic approach that incorporates ecologic and socio-economic principles. It strives to enhance biodiversity, soil health, and synergies between agroecosystem components, reduce reliance on synthetic inputs like pesticides, builds on Indigenous knowledge and local knowledge, and fosters social equity,” for example, by supporting fair, local markets.
Intercropping, livestock mobility, organic agriculture, cover cropping, and agroforestry are all practices that can benefit agroecosystems, the report states.
Aside from the fresh emphasis on NbS, the IPCC’s findings largely reflect an increase in evidence over the last several year on how climate change has had an adverse effect on land and water ecosystems. But the documented severity and extent of the impacts has increased, past predictions are now confirmed, and future predictions grow more likely.
The IPCC writes that multiple lines of evidence, combined with strong and consistent trends “observed on every continent,” make it very likely that noticeable changes in the ranges, life cycles, physiology, and morphology of terrestrial and freshwater species “can be attributed to regional and global climate changes,” particularly increases in frequency and severity of extreme events.
New studies find impacts “consistent with climate change” for more than 12,000 species globally. Of the 4,000-plus species where the attribution was assessed, approximately half had shifted their ranges to higher latitudes or elevations. “Shifts in species ranges are altering community make-up, with exotic species exhibiting greater ability to adapt to climate change than natives, especially in more northern latitudes, potentially leading to newly invasive species.”
High annual temperatures and heat waves due to climate change have resulted in “widespread” local population extinctions among plants and animals, and there have been at least three cases of global extinctions or near extinctions “linked to regional climate change.”
The IPCC found that at 1.5°C warming, 9 to 14% of species are likely to be at high risk of extinction. The percentage goes up with rising temperatures: 10 to 18% at 2°C, 12 to 29% at 3°C, 13 to 39% at 4°C, and 15 to 48% species are likely to risk extinction if global temperatures rise by 5°C.
Freshwater ecosystems will be affected by rising water temperatures in rivers and lakes and reductions in dissolved oxygen levels, the IPCC writes. On land, meanwhile, wildlife diseases and pests have increased in severity and outbreak frequency, and are spreading to new regions. Forest insect pests have expanded their ranges northward and ”severity and outbreak extent has increased” in northern North America and Eurasia.
Ecosystem changes are increasing, including “upward shifts in the forest/alpine tundra ecotone, northward shifts in the deciduous/boreal forest ecotones, increased woody vegetation in sub-Arctic tundra, and shifts in thermal habitat in lakes.” An ecotone is “a region of transition between two biological communities,” often rich in species.
These and other stresses from human activity affect ecosystem function, services, and resilience, says the IPCC.
In Canada, different studies found the deciduous forest shifting five kilometres northward into boreal conifer forest between 1970 and 2012, and 20 kilometres between 1970 and 2014. The temperate conifer forest shifted into the boreal conifer forest 21 kilometres between 1970 and 2015.
Regionally, areas subject to wildfires have increased up to double natural levels, and tree mortality has increased up to 20%. The report cites an increase in the area burned by wildfire 11 times higher than natural levels in one extreme year in British Columbia. Consequences include degradation of vegetation, habitat, water supplies, and other aspects of ecosystem integrity and services.
Increases in the area burned by wildfires range from 35% of global land at 2°C warming, to 40% at 4°C warming.
The report cites the key role of terrestrial ecosystems in storage and net removal of carbon from the atmosphere. However, a continued contribution is not assured. “Deforestation, draining and burning of peatlands, and thawing of Arctic permafrost due to climate change shifts these ecosystems from carbon sinks to carbon sources,” the scientists warn.
A section on climate-linked human illness reports growing evidence of increased risks of infectious disease transmission to humans. In combination with other factors, climate change is shifting the geographic and seasonal range of pathogens due to warming, extreme events, precipitation, and humidity. For example, the coastal area suitable for cholera has increased by 9.9% globally since 2000.