The climate potential of natural climate solutions
A concept that frequently comes up in the search for means to limit global warming is the idea of natural climate solutions (NCSs). These are ways of reducing greenhouse gas emissions caused by intensive land-use or of increasing carbon dioxide take-up by natural sinks. Scientists distinguish between two types of NCS: restoration measures and management measures. The first category covers approaches for returning landscapes and ecosystems to their natural state as carbon sinks, such as reforesting rainforests, mangrove swamps and boreal forests, or restoring former peatlands, salt marshes and seagrass meadows. Measures on or in the sea are often referred to as blue carbon approaches.
Management measures aim to improve the management of forest, arable land, grassland and peatland in order to increase the carbon content in their soil and vegetation and reduce their overall release of greenhouse gases. Field trials show that promising emission reductions can be obtained by means such as combining tree planting with arable crops or using manure or compost instead of artificial fertiliser.
Natural solutions could potentially have a huge climate impact if implemented on a global scale. Most are ready for deployment today, are cost-effective, and combine climate action with nature conservation, which is why they find favour with environmental organisations. According to recent studies, NCSs alone could boost carbon sinks on a scale equivalent to one-third of the emissions savings needed to achieve the 2 °C target.
However, there are also obstacles and limits to the global implementation of NCSs. Restoration measures need large areas of land that would then cease to be available for food production. The same applies to water resources. There is also the question of whether demand for timber and other materials could still be met with sustainably managed forests. One particular challenge is that there is no one-size-fits-all solution because different ecosystems have different requirements. Solutions that work in Europe cannot simply be transferred to other regions of the world but would have to be adapted.
The world would also need new policy instruments for the agricultural sector in order to enable carbon-oriented soil management. NCSs could be promoted by introducing a carbon tax. A good monitoring network would have to be set up to oversee the activities. It is also essential for the many stakeholders to be involved (farmers, consumers, retailers, etc.).
Decision makers should also bear in mind that the climate impact of natural climate solutions is finite. Carbon stored in the soil or in plant biomass only stays there as long as there is no adverse change in the climate, sustainable land use is kept up and, for example, trees are not felled and burned. It has also been shown that the climate balance of ecosystems such as peatlands and forests can tip over time, say when methane (also a greenhouse gas) is emitted or the land surface becomes darker in colour, which can drive additional heating.
The scientific community is divided on the question of how sensitive natural climate solutions themselves are to future climate change. Some researchers expect the CO2 absorption capacity of ecosystems to fall, while others predict that it will increase. It is undisputed, however, that deploying NCSs would have many positive side effects. These include improvements in air and water quality and the local climate, enhanced soil nutrient availability, increases in biodiversity and soil water retention, and heightened resilience of ecosystems to extreme climate-related events such as droughts. Scientists also expect large synergies. If a carbon tax were to be used to pay for the implementation of natural climate solutions, that would create a new income source for rural populations. ◆