Boreal Afforestation's Underestimated Cloud Influence on Earth's Energy Imbalance

TL;DR

Boreal afforestation impacts Earth's energy balance through complex cloud-related feedbacks, which can either cool or warm the planet, highlighting the need for climate-smart policies that consider these biophysical effects.

Contribution

This study introduces a decision-support framework that explicitly incorporates cloud-aerosol feedbacks in boreal afforestation planning, emphasizing their importance in climate mitigation.

Findings

Boreal forests can increase low-level cloud cover, producing cooling effects.

Snow masking from afforestation can cause surface warming.

Cloud-aerosol interactions may dominate under warmer conditions.

Abstract

Earth's Energy Imbalance (EEI) is accelerating, partly due to declining planetary albedo from reduced cloud cover. Boreal afforestation can either mitigate or exacerbate this trend through competing biophysical feedbacks. While snow masking reduces surface albedo (+0.5 to +2.5 $W/m^2$ warming), forests can enhance low-level cloud cover (0.1-0.5%) and increase cloud reflectivity via biogenic volatile organic compounds (BVOCs), producing potential cooling (-1.8 to -6.7 $W/m^2$). This BVOC-aerosol-cloud pathway remains poorly constrained but may dominate under warmer conditions, challenging carbon-centric mitigation paradigms. Large-scale initiatives (e.g., Canada's 2 Billion Tree Commitment) risk unintended warming if not climate-smartly sited. We present a tiered decision-support framework that integrates biogeochemical and biophysical processes, explicitly incorporating cloud-aerosol feedbacks. Urgent inclusion of these feedbacks in policy is essential to ensure boreal afforestation contributes to EEI stabilization.