Climate change could become the main driver of biodiversity decline by the middle of the century
Published on 25/04/2024
According to the large multi-model study published in Science on 26 April, global biodiversity may have declined between 2% and 11% during the 20th century due to human-induced land-use change alone. Projections show climate change could become the main driver of biodiversity decline by the mid-21st century.
Led by the German Centre for Integrative Biodiversity Research (iDiv) and the Martin Luther University Halle-Wittenberg (MLU), this analysis is the largest biodiversity and ecosystem services modelling study of its kind to date. Researchers compared no less than thirteen models for assessing the impact of both land-use change and climate change on four distinct biodiversity metrics, as well as on nine ecosystem services.
Nicolas Titeux, head of LIST’s Observatory for Climate, Environment and Biodiversity, played an active part in this groundbreaking research, which calls for renewed policy efforts to meet international biodiversity goals. He shared his knowledge on the relative roles of direct drivers of biodiversity change and the way they are integrated into large-scale models. He also ensured that the outcomes of this international collaboration were reflected in the Global Assessment Report of the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES).
Global Biodiversity may have declined by 2% to 11% due to land-use change alone
Land-use change is considered the largest driver of biodiversity change, according to the IPBES. However, scientists are divided on the extent to which biodiversity has changed in recent decades. To better answer this question, the researchers modelled the impacts of land-use change on biodiversity throughout the 20th century.
Based on historical reconstructions, they found that global biodiversity may have declined by 2% to 11% due to land-use change alone. This span covers four biodiversity metrics calculated by seven different models. More precisely, the scientists considered the global and local species richness (i.e. the number of species according to a defined scale), the mean species habitat extent and the biodiversity intactness (i.e. how much of an ecosystem's natural biodiversity remains despite human impacts).
Mixed trends for ecosystems services
Using another set of five models, the researchers also calculated the simultaneous impact of land-use change on so-called ecosystem services, i.e. the benefits nature provides to humans. In the past century, they found a massive increase in the provisioning of ecosystem services, like food and timber production, at the cost of regulating ecosystem services, like pollination, nitrogen retention, or carbon sequestration, which all declined moderately.
Climate and land-use change combined might lead to biodiversity loss in all global regions
The researchers also examined how biodiversity and ecosystem services might evolve in the future. For these projections, they added climate change to their estimations as a growing driver of biodiversity change.
Climate change stands to put additional strain on biodiversity and ecosystem services, according to the findings. While land-use change remains relevant, climate change could become the most important driver of biodiversity loss by the middle of the century. “Of course, these comparisons between drivers need to be interpreted with caution,” says co-author Nicolas Titeux. “There are differences in how models capture the impacts of climate and land-use change and in the spatial grain at which these impacts are estimated. This is part of the remaining modelling uncertainties identified by the study.”
The researchers assessed three widely-used scenarios – from a sustainable development to a high emissions scenario. For all scenarios, the combined impacts of land-use change and climate change result in biodiversity loss in all global regions. While the overall downward trend is consistent, there are considerable variations across global regions, models and scenarios, with the largest declines being projected in South America, Africa and South Asia.
Projections are not predictions
“The purpose of long-term scenarios is not to predict what will happen,” says co-author Inês Martins from the University of York. “Rather, it is to understand alternatives, and therefore avoid these trajectories, which might be least desirable, and select those that have positive outcomes. Trajectories depend on the policies we choose, and these decisions are made day by day.” Martins co-led the model analyses and is an alumna of iDiv and MLU.
The authors also note that even the most sustainable scenario assessed does not deploy all the policies that could be put in place to protect biodiversity in the coming decades. For instance, bioenergy deployment, one key component of the sustainability scenario, can contribute to mitigating climate change, as well as simultaneously reducing species habitats. In contrast, measures to increase the effectiveness and coverage of protected areas or large-scale rewilding were not explored in any of the scenarios. “This calls for a new generation of scenarios and models that aim to achieve realistic positive futures for biodiversity,” added Nicolas Titeux.
Models to help identify effective policies
Assessing the impacts of concrete policies on biodiversity helps identify those policies most effective for safeguarding and promoting biodiversity and ecosystem services, according to the researchers. “Our findings clearly show that current policies are insufficient to meet international biodiversity goals. We need renewed efforts to make progress with one of the world’s largest problems, which is human-caused biodiversity change.” conclude the authors.
Photo: Land-use change has been considered the largest driver of biodiversity decline in the 20th century. The photo shows an intensively managed grain field in Germany. (C) Guy Pe’er
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