Can boreal-forest monoterpene emissions regulate low-cloud albedo? A screening-level modelling feasibility study and risk analysis

Monoterpenes emitted by boreal forests oxidise into secondary organic aerosol (SOA) that can grow into cloud condensation nuclei and brighten low clouds, a process proposed as a natural climate feedback. This preprint asks whether the pathway could be deliberately regulated as a climate lever. A transparent, screening-level model chain (emission, oxidation, SOA, CCN, droplets, cloud albedo, radiative forcing) is propagated with a 20,000-member Monte Carlo ensemble over 24 uncertain parameters. Doubling emissions over the whole boreal biome gives a median regional forcing of about −0.23 W m−2 but only about −5.5 mW m−2 globally. A global forcing of −0.1 W m−2 is reached within a 10-fold emission increase in only 0.1% of members, and the cloud pathway saturates near −12 mW m−2 globally. An 11-item risk register highlights governance, hydrological side effects, verification difficulty and mitigation deterrence. The pathway is real but not a viable stand-alone climate intervention. This is a non-peer-reviewed screening study; model priors and risk scores have not been reviewed by domain experts Methods** : Python screening model (`bmcb_model.py`), Monte Carlo seed 20261024, N = 20,000.