Nature-based solutions (NbS) are neither a quick fix nor a perfect solution to tackle climate change. The sequestration of greenhouse gases by NbS takes place over long timescales relative to the rate that humans release greenhouse gases, and the effectiveness of these solutions is sustained only for as long as they remain permanent carbon sinks. However, well-designed nature-based solutions are a cost-effective way to tackle climate change that can also deliver other social, environmental and economic benefits. Enhancement of existing NbS and the creation of new ones is likely to play an important role in any long-term sustainable climate change strategy, working alongside engineered approaches. 

What are Nature-Based Solutions?

Nature-based Solutions began to be discussed in scientific papers in the early 2000s and represented a shift in attitude by researchers, policy makers and activists in their approach to tackling climate change. These solutions aim to protect and develop naturally-occurring ecosystems to help meet reduced emission targets and environmental goals. A key element of the nature-based solutions approach is enhanced carbon sequestration – the capture and storage of greenhouse gases. If countries are to achieve net-zero emissions, carbon dioxide, methane and nitrous oxide levels in the atmosphere must be stabilised and reduced. It is essential that these compounds remain stored, perhaps in plants or the oceans, and that the natural environment can continue to absorb greenhouse gasses.

Nature-based solutions sit alongside hard engineering approaches like carbon capture and storage as a way to achieve net-zero emissions. In particular, NbS could reduce pressure and reliance on strategies such as bio-energy with carbon capture and storage (BECCS), which is costly and limited by the amount of biomass that can be farmed. Other beneficial outcomes of NbS can include reducing flood risk, protecting biodiversity and improving air and water quality.

Despite the relatively recent use of the term in modern-day science, NbS have been utilised by Indigenous People and Local Communities (IPLCs) across the world for centuries to protect their local environments. Despite comprising less than 5% of the world’s population, IPLCs protect over 80% of biodiversity in areas that store at least 24% of the total carbon in global tropical forests. As explained in the report “Cornered by Protected Areas,” progress means adopting rights-based approaches to conservation that bring justice for IPLCs, whilst enabling biodiversity conservation and climate action.

Types of Nature-Based Solutions

There are three main types of NbS: 

Examples: Peatland rewetting, ceasing deforestation.

Examples: Agroforestry, reforestation and blue carbon initiatives

Examples: Establishing green buildings (includes green roofs and walls)

Each approach has different benefits to local communities and ecosystems and varying execution and upkeep costs.

Protection and Restoration of Peatlands and Wetlands

Peatlands are important ecosystems for regulating greenhouse gases in the atmosphere as undrained peatlands form large carbon sinks as a result of peat accumulation. Around 15% of the world’s peatlands, covering less than 0.4% of the global land surface, have been drained. Drainage of peatland emits huge amounts of CO2 into the atmosphere, so it is imperative we protect and restore these environments sustainably. This can be done through rewetting, raising the water table of peat bogs to increase greenhouse gas storage. Over time this greenhouse gas exchange can become close to that of a natural, undrained peatland. The solution has also been found to have a climate-cooling effect across various climate and land-use categories. Rewetting is a much more effective strategy than peatland initiation which can take much longer and still not store equivalent amounts of carbon and nitrogen as older peatlands.

Forestry Solutions

Deforestation and forest degradation releases an estimated 4.4Gt of CO2 every year (equivalent to 10% of annual global CO2 emissions), so preserving existing forest is a quick win.

Reforestation is the most familiar and recognisable NbS; trees absorb and sequestrate carbon dioxide. However, the solution is more complex, and reforestation should only be part of a wider strategy, particularly if short-cuts are taken which risk creating monocultures and introducing invasive species into local ecosystems. It has been estimated that by restoring 350 million hectares of degraded forest landscapes  by 2030, an area twice the size of Alaska, 1-3 Gt of CO2 could be sequestered per year. However there are obvious logistical barriers to this which have been debated in scientific articles. Despite this, the solution is highly cost-effective and therefore easier to promote amongst private stakeholders and governments concerned with short-term returns. 

A lot of agricultural land across the world is already degraded, with climate change expected to exacerbate the loss of soil-organic carbon (SOC) through processes such as decomposition, mineralisation and erosion. To minimise these emissions, SOC stocks need to be protected whilst carbon saturation levels are increased. Methods include agroforestry – the planting of trees amongst crops which allows farmers to maintain yield sizes in cases of climate variability. This method also reduces soil erosion and limits the loss of soil organic carbon whilst increasing the ability of agricultural land to sequester greenhouse gases.

Successful forestry initiatives reward farmers and landowners for providing environmental benefits. A frequently cited success story is the Payment for Ecosystem Services (PES) scheme in Costa Rica. Christina Figueres, the former Executive Secretary of the UNFCCC, has commended using taxes as a way to fund better agricultural practices. PES is a strategy that was adopted by Costa Rica in 1996 to confront its huge deforestation problem. It is estimated that the strategy prevented 11 million tonnes of carbon emissions being released between 1999 and 2005, with Costa Rica’s forest cover actually increasing over the last 20 years despite continued, managed deforestation. There are still improvements to be made, as Costa Rica PES is limited by a flat-rate payment scheme that benefits farmers with smaller land parcels, restricting larger-scale implementation. Most PES plans are funded by national governments and involve intermediaries, usually non-governmental organisations (NGOs), proving that communication and cooperation between governments, NGOs and private stakeholders is crucial if a system is to be implemented and sustained successfully.

Blue Carbon

71% of the Earth’s surface is water. So called ‘blue carbon’ includes carbon captured and stored in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds and salt marshes. Since the 1980s, between 20-30% of anthropogenically produced CO2 emissions have been captured in oceans, contributing to ocean acidification. The key benefit of blue carbon storage is their ability to increase their carbon capacity over time, unlike forests which can reach a saturation point and can only store carbon for decades or centuries at most. There is also a lot of ongoing research into the nature of other marine NbS, which may reduce the strain of ocean-acidification on vulnerable ecosystems such as coral reefs. Kelp forests are particularly interesting examples of NbS as the nature of the plant, a macroalgae, means it can float for long distances out to sea and therefore its carbon content can be sequestered in deep ocean stores. However, these potential solutions need more research and investment and are unlikely to assist materially in achieving 2030 and 2050 emission targets unless progress is significantly accelerated.

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Climate Mitigation Potential

The 2014 Climate Change Synthesis Report published by the IPCC states that “stabilising temperature increase to below 2°C relative to pre-industrial levels will require an urgent and fundamental departure from business as usual.” Nature-based solutions are a key component to achieve net-zero emissions, and crucially are more beneficial and acceptable to communities that want to protect and restore their natural environment without hard engineering methods. Cost‐effective nature-based solutions can provide around 30% of immediate climate mitigation needs through protection, management, and restoration of ecosystems. However, the true mitigation potential is still unknown as environmental-based approaches have disproportionately struggled from lack of investment and research

Nature-based solutions also work best over long timescales; they are no ‘quick fix’ to the net-zero goal as they require huge amounts of land, water resources and time to reach their carbon saturation and mitigation potential. For example, whilst older trees have larger stores of carbon the ability of forests to sequester carbon decreases with age, and some of the carbon may be rapidly released by wildfires (which in turn rejuvenates the forest).

Cost-Effectiveness

The implementation and maintenance costs of NbS are often offset by the benefits, for example disaster risk management along river catchments and in coastal regions. Natural flood management is a pressing concern in places like the UK, believed to be exacerbated by the impacts of climate change. Solutions such as regenerating natural woodland within a river catchment and constructing leaky dams have been found to reduce the hazards of flooding on smaller catchments, although not for more extreme events.

Nature-based solutions are seen as multi-functional solutions that can manage carbon dioxide sequestration whilst also improving water security, food security and human health, however this holistic approach can make  cost-analysis models more complicated due to the difficulty of attributing economic value to these benefits. Recent advancements in environmental modelling have helped reduce uncertainties and illustrate the varying levels of protection different NbS can offer, for example, reducing the frequency and intensity of natural hazards like flooding.

More research needs to be conducted to ensure planning applications address concerns about balancing present costs with future benefits. Part of the appeal of engineered solutions is their fixed costs, short timescales and relatively certain outcomes. There is widespread consensus among policy makers, ecologists, engineers and geomorphologists that a combination of nature-based solutions and engineered solutions is often optimal to protect a specific environment. For example constructing vegetated levees and managing wetlands outside New York to protect against storm surges like those produced by Hurricane Sandy in 2012. 

Challenges of the Nature-Based Solutions Approach to Tackle Climate Change

A huge challenge to implementing NbS is water availability, which these strategies invariably require in huge quantities. Water scarcity is already a significant problem in many regions, for example the Middle East and North Africa.  Another limiting factor is the lack of available space, as with an ever-growing global population, productive land is in increasingly short supply. Therefore multi-functional landscapes that sequester carbon whilst delivering other valuable benefits such as food production, preservation of biodiversity and risk mitigation are preferred for NbS interventions. However, these benefits may vary in both their spatial and temporal distribution. Therefore coordinated action between stakeholders, the public and policy makers is required, with policy interventions designed to ensure decisions are rewarded (or penalised) by the benefits (or costs) that accrue to all stakeholders, not just to decision-makers. Ultimately, NbS can only work in conjunction with other strategies if they are implemented sooner rather than later, and in a way that respects and protects the ecosystems and communities that are to be altered.