IPCC Assessment in depth, Part 13: What role can nature-based solutions play in adaptation and mitigation?

The threat that climate change poses to human well-being and the health of the planet is “unequivocal”, says the latest report from the United Nations’ Intergovernmental Panel on Climate Change (IPCC). In this in-depth Q&A series, Carbon Brief unpacks the key findings of the report and the developments since the IPCC’s last assessment. (Read previous section here)

By Carbon Brief

13. What role can nature-based solutions play in adaptation and mitigation?

Many sections of the report deal with the effectiveness of “nature-based solutions” in climate change adaptation and mitigation.

In its current definition, the report accepts with high confidence that nature-based solutions (NbS) “provide adaptation and mitigation benefits for climate change as well as contributing to other sustainable development goals”.

The authors note that while NbS is “not a universally accepted term…it is increasingly used in the scientific literature”. They recognise that its definition excludes actions that use nature to “solve human problems but do not provide benefits for biodiversity”. The SPM adds that the term is “the subject of ongoing debate, with concerns that it may lead to the misunderstanding that NbS on its own can provide a global solution to climate change”.

The authors state that “ecosystem based adaptation” (EbA) – which aims to increase resilience and reduce vulnerability of ecosystems to help people adapt – could be a subset of NbS, while observing that both NbS and EbA are “themselves vulnerable to climate change impacts”.

The authors agree there is robust evidence that these solutions for people and climate can also benefit wild species and habitats, and often contribute to other SDGs.

However, “poorly conceived and designed” nature-based mitigation projects have the potential for multiple negative impacts, says the report with high confidence. They could create or exacerbate competition for land and water resources, “reduc[e] human well-being” or fail to provide mitigation that is sustainable in the long-term”.

For NbS to succeed, the report says with high confidence that it is “critical” that they support local livelihoods. “[I]ndigenous, local communities and millions of private landowners” should benefit, and be actively engaged in decision-making around NbS.

The study authors observe with high confidence that “nature-based solutions cannot be regarded as an alternative to, or a reason to delay, deep cuts in greenhouse gas emissions”. 

A separate cross-chapter box in Chapter 2 examines the definitions and effectiveness of NbS, from forests and peatlands to blue carbon and urban NbS.

Forests

Keeping “existing natural forests” standing and sustainably managing “semi-natural forests” “is a highly effective NbS”, the report says with high confidence.

Protecting natural forests currently contributes between 5-7bn tonnes of CO2 per year (GtCO2/year) to climate mitigation efforts, it estimates.

The assessment states with high confidence that reforestation “can be one of the most practical and cost-effective ways of sequestering and storing carbon”, while also protecting and helping biodiversity recover – particularly if carried out with “climate-resilient native or geographically near species”. It can also help improve water supply and quality in ecosystems and reduce the risk of floods and soil erosion.

Wildfires, droughts and pest outbreaks count as severe disturbances that can cause tree mortality, pushing stored forest carbon back into the atmosphere, the report notes. These disturbances are on the rise because of climate change, prompting a “need to adapt”.

Ecological restoration with diverse species “rather than monoculture plantations” can help reduce these risks.

The report notes with very high confidence that mono-culture plantations that fail to plan for their host landscapes, do not “meaningful[ly] engage” with Indigenous and local communities, or seek their “free prior and informed consent” can “present risks to biodiversity, rights, livelihoods and wellbeing, as well as being less climate-resilient than natural forests”.

In addition, the report warns with high confidence that afforesting savannahs, natural peatlands and other areas that do not naturally house forests “damages biodiversity and increase[s] vulnerability to climate change…so is not a Nature-based Solution and can exacerbate greenhouse gas emissions”.

It says that remote-sensing studies can often overestimate land available for tree-planting potential, as they can fail to distinguish “between degraded forest and naturally open areas”.

Peatlands

Peatlands are “naturally high-carbon ecosystems, which have built up over millennia”, the report says. Draining, cutting and burning peat

lead to the release of CO2, the authors say with very high confidence.

Rewetting dried peatlands and preventing further cutting and burning can help restore some temperate peatlands, but “this is a process that could take many years”.

Protecting intact “peat forests” – tropical moist forests in swampy soil – “is by far the more effective pathway both in terms of cost, CO2 mitigation and protection of food sources”, the report notes.

In some cases, naturally treeless northern hemisphere peatlands have been drained to enable trees to be planted.

This “leads to CO2 emissions”, the authors say with high confidence, and restoration “requires removal of trees as well as re-blocking drainage”.

Agroecology and agroforestry

The report considers the strategies of agroforestry and agroecology. Agroforestry refers to the integration of trees and shrubs with crops and livestock in agricultural systems. Agroecology, as the report defines, is a set of practices including “intercropping, livestock grazing mobility, organic agriculture, integration of livestock, fish and cropping, cover crops and agroforestry”.

Studies assessed in the report demonstrate that agroforestry can store 20-33% more soil carbon than conventional agriculture while also reducing fire risk.

The mitigation potential of “agroecologically-improved cropland and grazing land management” is “significant” and estimated at 2.8-4.1GtCO2e per year.

Minimising nitrogen-based fertilisers and other synthetic inputs reduces emissions, while cover crops can increase soil carbon and reduce nitrous oxide emissions, the report says. Biodiverse agroforestry systems benefit nature and people more than simple agroforestry and conventional agriculture, it adds.

While yields in agroforestry and organic farming are sometimes lower than intensive agriculture, the report states with medium confidence that agroforestry “can boost productivity and profit” over varying timeframes, based on the socioeconomic, political and ecosystem context.

The authors agree with high confidence that adopting agroecology principles and practices would be “highly beneficial” to maintain “healthy, productive food systems under climate change”.

Blue carbon and oceans

“Blue carbon strategies” – which rely on ecosystems such as mangroves, marshes and seagrass meadows for their mitigation potential – are

still “relatively new, with many of them experimental and small scale”, the report notes.

While there is evidence to show that blue carbon systems often have high local rates of carbon accumulation and storage, their overall mitigation value as NbS is hard to estimate due to the “variable production” of other greenhouse gases. For example, restoring water flow in mangroves and marshes could potentially reduce methane and nitrous oxide emissions, but evidence is limited.

The report concludes with medium confidence that blue carbon strategies “can be effective NbS” for climate mitigation, but their overall global or regional potential “may be limited”. However, there is high confidence that these systems can “counteract sea level rise effects, buffer storm surges and flooding erosions”, providing climate adaptation, biodiversity, cultural and socio-economic benefits.

Restoring dunes and coastal wetlands to reduce coastal risks and act as a buffer between infrastructure and the sea yields immediate benefits, the report says, but these solutions “are not feasible everywhere”, especially in urbanised areas.

There are limits to adaptation to accelerating sea level rise – including in geographies such as the Mediterranean – the authors note in Cross-Chapter Paper 4. This, in turn, has stimulated ideas of large-scale “geoengineering projects” such as surface height control dams at Gibraltar, which “come with unknown risks for humans and ecosystems”. Engineering-based coastal adaptation “could result in large residual impacts to coastal ecosystems”, the report notes with high confidence.

In Chapter 3, the authors state with high confidence that, when well-designed and implemented, NbS for ocean and coastal adaptation can be “cost-effective” and “achieve multiple benefits” and “can contribute to the conservation of biodiversity in the near to mid-term”. However, their effectiveness declines with warming and must be accompanied by “urgent mitigation”.

For instance, the report says “conservation and restoration alone will be insufficient” to protect coral reefs beyond 2030 and mangroves beyond the 2040s.

While marine protected areas do not prevent marine heatwaves, they can increase

climate resilience “by removing additional stressors” and “providing “marine plants and animals with a better chance to adapt to a changing climate”, it says.

The report considers sustainable fishing to be an NbS, because sustainably managing marine commercial species “maximises the catch and food production”, thus contributing to the UN’s zero hunger goal.

The figure below examines marine and coastal NbS and their feasibility and effectiveness in alleviating climate risks in the medium term. The weight of the outline surrounding boxes indicates confidence in the solution’s potential, based on observed evidence. Each solution’s feasibility and effectiveness are ranked by dots in blue and red respectively, based on its ability to support ecosystems and communities as they adapt.

Urban NbS

Carefully designed urban greening in cities and “well-functioning ecosystems can play a significant role in buffering cities, settlements and

infrastructure from climate hazards at multiple scales”, the report states.

Investing in “green and blue infrastructure” and natural area conservation in cities are “widely recognised as low-regret measures for disaster risk reduction and climate change adaptation”. From reducing temperature shocks and providing natural flood defences to physical and mental health co-benefits, urban NbS provide many “adaptation and resilience benefits”, the authors note.

Street trees, green roofs, green walls and other urban vegetation are among the strategies it lists that can reduce extreme heat by cooling private and public spaces.

Outdoor green spaces may also slightly reduce indoor heat risks and contribute to lower energy costs, it says. Studies assessed show that homes with shade trees “in cities where air conditioning systems are common can save over 30% of residential peak cooling demand”.

The report says “not all green schemes” in cities should be considered NbS, especially if they do not benefit biodiversity.

It points to studies of how schemes could cause “green gentrification, which offers nature based solutions to the few”, increase water demand or public use. The report advises careful planning with equity consequences in mind, so that wealthy neighbourhoods do not benefit more than the poor.

Wetland restoration close to settlements should be paired with mosquito control to safeguard public health, but is extremely effective at reducing toxicity and improving water filtration, the report says.

There is robust evidence that “urban parks and open spaces, forests, wetlands, green roofs and engineered stormwater treatment devices” reduce stormwater runoff, surface

flooding, and contamination of runoff by pollutants.

Similarly, authors are in high agreement that coastal ecosystems can reduce impacts of coastal flooding and storms in cities. For instance, vegetation and reefs can “dissipate wave energy”, reduce water levels and shoreline erosion, with “potential to save lives and prevent expensive property damage”. However, “coastal habitats also have limitations in their ability to protect coasts from extreme events”, including tsunamis.

Urban farming can serve as a NbS for food security and already does so for poor communities, the report notes, but land availability “can be further constrained by land-use history, including past industrial uses”.

Approval session

Including the term “nature-based solutions” in the SPM was heavily contested during the SPM approval session. According to Third World Network, “developed countries led by France advocated for [NbS] as a measure to reduce climate risks to people, biodiversity and ecosystem services and to treat it on par with ecosystem-based adaptation”.

However, developing countries “led by South Africa” argued that the term was contentious. According to the Earth Negotiations Bulletin (ENB), South Africa, India and Ecuador “insisted that the NbS concept is highly problematic and that just because it exists in the literature does not mean it should be taken up by the IPCC”, calling for its removal or “not having it in Section C linked to adaptation”, as suggested by India. India reportedly said the term comes from a “European urbanised context” and that its problem was the word “solutions”, which “brushed the need for mitigation under the carpet”.

Eventually, “nature-based solutions” was negotiated to a footnote in the SPM. The SPM adds that the term is “the subject of ongoing debate, with concerns that it may lead to the misunderstanding that NbS on its own can provide a global solution to climate change”.

In addition, Argentina’s proposal to reference the Convention on Biological Diversity (CBD) in the footnote – set to negotiate a new agreement for nature this year – was opposed by the US, India and others, ENB says.

All sections:

1. What is the IPCC report?
2. How is climate change affecting land ecosystems?
3. What impact is global warming having on marine life?
4. How is climate change affecting the world’s water?
5. What does the IPCC report say about impacts on food and agriculture?
6. What risks does climate change pose to the world’s cities?
7. What does the report say about public health, conflict and migration?
8. How does climate change affect poverty and progress towards the sustainable development goals?
9. How is the world adapting to climate change?
10. Are there limits to what adaptation can achieve?
11. What does the report say about ‘loss and damage’?
12. What are the risks of ‘maladaptation’ and the unintended consequences of tackling climate change?
13. What the latest IPCC report says about carbon fee and dividend

Authors:

Aruna Chandrasekhar holds an MSc in environmental change and management from the University of Oxford. She previously worked as a freelance journalist for a variety of publications, including the New York Times, Guardian, Scroll and Caravan.

Daisy Dunne holds a BSc in biology from the University of Bristol and a science journalism MA from City, University of London. She was The Independent’s climate correspondent from November 2020 to 2021. Prior to this, she was Carbon Brief’s science writer from 2017 to 2020.

Josh Gabbatiss covers climate and energy policy. Josh holds a BSc in zoology from the University of Bristol. He previously worked as science correspondent at The Independent and prior to that was a freelance journalist for a variety of scientific publications including New Scientist and BBC Earth.