1,2,3,5,6- 1Institute for Advanced Studies (Collegium Helveticum), ETH Zurich and the University of Zurich, Zurich, Switzerland
- 2Epidemiology, Biostatistics and Prevention Institute (EBPI), Department of Global Health, University of Zurich, Zurich, Switzerland
- 3Institute for Atmospheric and Climate Science, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
- 4Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland
- 5Institute for Terrestrial Ecosystems, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
- 6Global Ecosystem Ecology Lab, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
- 7Environmental Science and Engineering Division, KAUST, Saudi Arabia
Forests are powerful climate regulators: Their CO2 uptake provides a global biogeochemical cooling effect, and in the tropics, this cooling is further strengthened by evapotranspiration. Given that temperature-related mortality is a relevant global health burden, which is expected to increase under climate change, we set out to test what we thought was a promising hypothesis: Can forests reduce human temperature-related mortality from climate change?
To test this, we used simulated temperature changes to reforestation from six different Earth System Models (ESMs) under a future high-emission scenario, and paired them with age-specific population data and three methodologically different temperature-mortality frameworks (Cromar et al. 2022, Lee et al. 2019, and Carleton et al. 2022). We expected to find a plausible range of temperature-related mortality outcomes attributable to global future forests conservation efforts.
Instead, our idea ran head-first into a messy reality. Firstly, rather than showing a clear consensus, the ESMs produced a wide range of temperature responses to reforestation, varying both in magnitude and sign. This is likely due to the albedo effect, varying climatological tree cover and land use processes implemented by the models, in addition to internal variability which we could not reduce due to the existence of only one ensemble member per model. Consequently, the models disagreed in many regions on whether global forest conservation and reforestation would increase or decrease temperature by the end of the century.
The uncertainties deepened when we incorporated the mortality data. Mortality estimates varied by up to a factor of 10 depending on the ESM and mortality framework used. Therefore, in the end, the models could not even agree on whether forests increased or decreased temperature-related mortality. We found ourselves with a pipeline that amplified uncertainties of both the ESM and mortality datasets.
For now, the question remains wide open: Do trees save us from temperature-related deaths in a warming world, and if so, by how much?
* The first two authors contributed equally to this work.
How to cite: Hohmuth, N., Fahrenbach (presenting), N. L. S., Zou (presenting), Y., Reek, J., Specker, F., Crowther, T., and Zohner, C. M.: Do trees save lives under climate change? It’s complicated , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8359, https://doi.org/10.5194/egusphere-egu26-8359, 2026.
