Climate change and biodiversity loss amplify each other’s impacts

Key messages

• Climate change is impacting biodiversity from local to global scales, and growing evidence suggests that further loss of biodiversity can contribute to climate change, creating a destabilising feedback.
• Loss of plant diversity due to climate and land use change can weaken ecosystem functioning, leading to a decrease in biomass accumulation and reduced carbon storage.
• Natural climate solution initiatives that integrate aspects of ecosystem integrity and species composition, rather than focusing solely on land cover area, can more effectively safeguard the carbon sink function.

Climate change and biodiversity loss are two of our most pressing and interlinked environmental challenges. Multiple studies demonstrate the potential impact of climate change on biodiversity at local to global scales: 3–6 million (or more) animal and plant species are threatened, even under intermediate climate change scenarios. There is also growing evidence that a loss of biodiversity contributes to destabilising feedback, directly impacting climate stability. Studies consistently find that higher plant diversity on land can increase ecosystem functioning, including carbon storage, and these effects grow stronger as time goes on (see Table 1 for the mechanisms).

Because higher plant diversity leads to greater biomass within a place over time, loss of plant diversity from climate and land use change can lead to decrease in biomass and reduced carbon storage. A recent study found that projected global plant-
species loss could lead to the emission of 7–146 GtC in the coming decades (Figure 4). Although the uncertainty range is large, the high-end estimates constitute a substantial portion of the remaining carbon budget before warming exceeds 1.5 or 2°C. Similarly, conserving tree diversity through climate change mitigation could correspond to 2–3 GtC/yr in reduced emissions.

While tree diversity can enhance carbon sequestration and retention in agroforestry systems, it remains less clear whether increasing plant diversity within cropland agroecosystems can have a similar effect. A large field trial that combined under-sown species with a cereal crop showed that increasing plant diversity within agroecosystems can increase the carbon retention potential in soils without compromising productivity. This confirms previous studies suggesting that manipulating plant diversity can enhance plant productivity and positively influence the associations between microorganisms, increasing microbial growth efficiency, which is considered a driver of soil carbon storage.

Though the role of plant diversity on ecosystem functioning is well established, the strength of the relationship can vary across biomes and environmental conditions. Large-scale analyses have shown stronger biodiversity-productivity relationships in less productive ecosystems. Similarly, studies have found that the effects of plant diversity on soil organic carbon storage were stronger at drier sites. To reduce uncertainties, research across distinct biomes, environmental gradients, and in different species is needed to clarify the ecological mechanisms underlying variations in the biodiversity–carbon storage relationship.

Plant-animal interactions, for instance through trophic chains, and ecosystem functions can potentially alter vegetation structure and plant species composition, which in turn can affect above- and belowground biomass. For example, studies show that elephants in African forests increase aboveground biomass, though in African savannas, fewer herbivores resulted in higher biomass. In tropical systems, human-induced reductions in animal species could reduce carbon storage by up to 26%, primarily through population declines in animal-dispersed tree species. In the Brazilian Atlantic Forest, a study quantified that frugivores – who eat plant fruit, nuts, shoots, roots and seeds – can potentially enhance carbon recovery in fragmented forest landscapes when at least 40% forest cover remains. But these species may be disproportionately affected by climate change, especially in the tropics. Independent of these species interactions, evidence demonstrating the role of terrestrial animals as contributors to climate solutions is limited and remains contested.

Animals can also impact carbon storage in the oceans. Thanks to their large size, whales sequester carbon as biomass, which sinks to the ocean floor after their death. The recovery of baleen whale populations and their nutrient recycling services could enhance productivity and help restore ecosystem functions lost during 20th-century whaling, though the carbon benefits associated with this recovery are increasingly threatened by climate change.

Multidisciplinary and transdisciplinary approaches to understanding the social, ecological, and physical processes involving biodiversity loss and climate change through carbon uptake, release, and protection are critical in assessing destabilising feedback mechanisms. Because of this feedback, meeting the targets of the Kunming-Montreal Global Biodiversity Framework (KMGBF) can directly contribute to countries’ Nationally Determined Contributions under the UNFCCC by reducing biodiversity-loss-driven carbon debt. Recognising and acting upon the interdependence between biodiversity conservation and restoration and effective climate mitigation are needed to effectively tackle climate and biodiversity policy targets. Despite the importance of biodiversity in carbon storage, many existing natural climate solution initiatives focus on ecosystem extent and cover, rather than on quality and composition, which impact the effectiveness of the carbon sink. Maintaining and restoring diverse ecosystems while considering Indigenous and traditional knowledge and livelihoods can be an effective step towards achieving sustainability in the face of multiple global crises and therefore towards contributing to both KMGBF and NDC agreements. Indigenous Peoples and local communities contribute location- and biome-specific knowledge that informs local policies and supports global goals.