Land Models Likely Underestimate the Impact of Future Atmospheric Dryness on European Tree Growth

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2026GL122759

Authors: Brendan Clark, Daniele Visioni, Shan Kothari, Manuel Lerdau

First published: 18 June 2026

https://doi.org/10.1029/2026GL122759

Abstract

Understanding how the land carbon sink will be altered by climate change is critical for projecting future atmospheric CO2 concentrations under different emission pathways in Earth System Models (ESMs). Most land models assume that woody growth, the main driver of land carbon storage, is driven by photosynthetic carbon supply. In reality, growth is often constrained by physiological processes limiting cell division independent of carbon availability, like reduced turgor pressure. Rising vapor pressure deficit (VPD) under climate change reduces turgor pressure and suppresses actual growth more strongly than photosynthesis, suggesting ESMs may overestimate future terrestrial carbon uptake. We compare simulations of the Community Land Model (CLM) to a statistical model built on dendrometer observations, showing that CLM underestimates decreases to growth under elevated VPD by a factor of 2–3. This highlights the need for land models to represent physiological constraints on tree growth to improve projections of future terrestrial carbon uptake.

Plain Language Summary

The land surface absorbs about a third of human carbon dioxide emissions. Climate change is expected to impact tree growth, and global numerical models are used to make predictions of how that will impact the land's ability to store carbon in the future. As the air becomes drier under climate change, it causes trees to close their stomata, reducing photosynthesis. However, dry air can also directly slow tree growth by limiting cell division and expansion. This process is not included in global numerical models, yet it can be more sensitive to the drying of air than photosynthesis. We show that a widely used global land model underestimates how much drying air in the future may reduce tree growth, which could have important implications for projections of carbon storage and future climate change.

Source: AGU