Climate change could become the main driver of biodiversity decline by mid-century

The analysis was led by the German Centre for Integrative Biodiversity Research (iDiv) and the Martin Luther University Halle-Wittenberg (MLU) and is the largest modelling study of its kind to date. The researchers compared thirteen models for assessing the impact of land-use change and climate change on four distinct biodiversity metrics, as well as on nine ecosystem services.

Two scientists at the Environmental Change Institute (ECI) contributed to the main body of research in former roles before joining the ECI. Prof Professor Michael Obersteiner, Director, ECI and Professor of Global Change and Sustainability, worked on the Shared Socio-Economic Pathways and more recently the cSAR-IIASA-ETH biodiversity model while at the International Institute for Applied System Analysis, Laxenburg, Austria.

Dr Tom Harwood, Associate Director, ECI, contributed analyses using the 1km resolution BILBI modelling system which is specifically designed to consistently tackle the combined effects of land use and global change, and the downscaling of the LUH2 dataset used by the finer modelling contributions in the ensemble. He developed and managed the infrastructure at CSIRO in Australia. Dr Harwood said:

These results are consistent with our results over the past 15 years, showing that the projected impact of climate change on biodiversity will soon drown out the impacts from land use change. Given the magnitude of projected climate change, and the emergence of novel environmental conditions, this is only to be expected.

 

In terms of the agreed Goals to halt and reduce species extinctions by 2050 in the Kunming-Montreal Global Biodiversity Framework, this is a big problem. These goals cannot realistically be achieved unless we first halt and reverse climate change.”

Land-use change is considered the largest driver of biodiversity change, according to the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES). However, scientists are divided over how much biodiversity has changed in past decades. To better answer this question, the researchers modelled the impacts of land-use change on biodiversity over the 20th century. They found global biodiversity may have declined by 2% to 11% due to land-use change alone. This span covers a range of four biodiversity metrics1 calculated by seven different models.

Lead author, Prof Henrique Pereira, research group head at iDiv and MLU, said: 

By including all world regions in our model, we were able to fill many blind spots and address criticism of other approaches working with fragmented and potentially biased data. Every approach has its ups and downsides. We believe our modelling approach provides the most comprehensive estimate of biodiversity trends worldwide.”

Using another set of five models, the researchers also calculated the simultaneous impact of land-use change on so-called ecosystem services, ie, the benefits nature provides to humans. In the past century, they found a massive increase in provisioning ecosystem services, like food and timber production. By contrast, regulating ecosystem services, like pollination, nitrogen retention, or carbon sequestration, moderately declined.

The researchers also examined how biodiversity and ecosystem services might evolve in the future. For these projections, they added climate change as a growing driver of biodiversity change to their calculations.

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 mid-century. The researchers assessed three widely-used scenarios – from a sustainable development to a high emissions scenario. 

For all scenarios, the impacts of land-use change and climate change combined result in biodiversity loss in all world regions.

While the overall downward trend is consistent, there are considerable variations across world regions, models, and scenarios.

“The purpose of long-term scenarios is not to predict what will happen,” says co-author Dr 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.” 

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, but can simultaneously reduce 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.

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. Pereira adds. “There are modelling uncertainties, for sure. Still, our findings clearly show that current policies are insufficient to meet international biodiversity goals. We need renewed efforts to make progress against one of the world’s largest problems, which is human-caused biodiversity change.”

Read the paper in full: Global trends and scenarios for terrestrial biodiversity and ecosystem services from 1900 to 2050