Does Solar Geoengineering Delay Amazon Dieback?

Assessments of Amazon rainforest dieback have primarily focused on the magnitude of forest loss under transient climate change, while less attention has been paid to the rate, variability, and commitment of ecosystem decline under alternative climate intervention pathways. The concept of realized and committed ecosystem change has shown that Amazon forest loss can be effectively locked in long before it becomes observable (Jones, C. et al., 2009), while recent policy-oriented assessments demonstrate that such commitments remain a substantial risk even under 1.5 °C stabilization and overshoot pathways (Munday, G. et al., 2025). This study explores whether solar geoengineering modifies long-term Amazon forest commitment or primarily alters the timing and variability of dieback.

Here, we propose to extend the concept of committed ecosystem change to quantify the speed and temporal variability of Amazon forest dieback under scenarios with and without stratospheric aerosol injection (SAI). Using the Met Office Hadley Centre climate carbon cycle model HadCM3, we will analyse transient and equilibrium forest responses to stabilized forcing states derived from high emission baseline scenarios.

The analysis follows the realized and committed ecosystem framework developed in earlier coupled climate vegetation studies using HadCM3 (Jones, C. et al., 2009) without solar geoengineering. We first reproduce this analysis under a non-SAI baseline and subsequently apply the same diagnostics to simulations from the UK Earth System Model (UKESM) incorporating stratospheric aerosol injection, enabling a consistent comparison of Amazon dieback speed and variability across scenarios.

For each scenario, we distinguish between realized (time evolving) and committed (equilibrium) states of Amazon forest cover, using equilibrium diagnostics to estimate the long-term ecosystem response to fixed climate conditions. Dieback speed will be defined as the rate of fractional forest loss per degree of global mean temperature change, while variability will be assessed through interannual and decadal fluctuations in forest cover and associated hydroclimatic drivers. This analysis is expected to provide preliminary insights into whether SAI delays or modifies the rate and variability of Amazon forest dieback, while potentially leaving committed long-term losses largely unchanged once critical climatic thresholds are exceeded. As this study is at an early stage, the results will be exploratory in nature and intended to provide a first-order assessment of potential ecosystem risks associated with solar geoengineering rather than definitive projections.

Reference

• Jones, C., Lowe, J., Liddicoat, S. et al. Committed terrestrial ecosystem changes due to climate change. Nature Geosci 2, 484–487 (2009). https://doi.org/10.1038/ngeo555
• Munday, G., Jones, C.D., Steinert, N.J. et al. Risks of unavoidable impacts on forests at 1.5 °C with and without overshoot. Nat. Clim. Chang. 15, 650–655 (2025). https://doi.org/10.1038/s41558-025-02327-9