The Case for a Pre-industrial Aerosol Forcing and Impacts of Cleaner Air on Regional Climate Change: Urgent Call for Precautionary Mitigation and Adaptation

This research attempts to reassess, using observation and latest literature studies, the importance of anthropogenic aerosol changes over the past 6000 years to present on regional and global climate forcings and its strong impact on the rate of climate change. Recent research studies (Hansen et al. 2023 & 2025) reveals that a better assimilation of higher aerosol forcing can help to explain the Holocene (temperature) conundrum (a stable Holocene climate, while greenhouse concentrations increased). Such an aerosol forcing has strong impact on paleo- and present climate change.

To this day, pre-industrial anthropogenic aerosol forcing sources remain, including harmful slash and burn agriculture and biomass cooking. But regulations and technologies for aerosol mitigation are present and in the pipeline. 

This contributes to regional and global forcing changes, combined with mitigation from industrial aerosol sources like coal plant desulphurisation and notably, since the implementation of stringent sulphur regulations by the International Maritime Organization (IMO) in 2015 and 2020, mitigation of aerosols and aerosol cloud interactions over the dark (low albedo), relatively cold oceans, which act as the primary planetary heat sink of Earth’s Energy Imbalance. More strict regional sulphur regulations will soon come into effect.

Recent forcing estimates from IMO regulations vary widely, from only 0.08 W/m² based on a simple climate model (Hausfather & Forster 2023 using FaIR) to up to 0.50 W/m² based on observations (Hansen et al. 2025). Our analysis, based on NASA CERES satellite data, reveals that the active shipping region of the North Atlantic (20-60N) has experienced a 4-year averaged increase in Absorbed Solar Radiation of 3.0 W/m² and a regional Net flux increase of 1.4 W/m² since 2014, with estimated impacts on regional warming, extreme weather and on the Atlantic Meridional Overturning Circulation (AMOC).

These rapid reductions in aerosol (precursor) emissions combined with a high greenhouse gas (GHG) forcing (currently about +4 W/m² above 1750) may lead to regional, and potentially global, aerosol termination shocks, whereby the reduction of aerosols in absence of GHG reductions increases the rate of warming by >0.2°C/dec. And latest observations are already signalling a potential earlier than anticipated approach to climate tipping points (incl. coral reef die-off; AMOC slow down; and reducing Amazon rainforest and boreal forest carbon sinks), with underestimated climate sensitivities.

Because strong scientific uncertainties remain, we highlight the necessity, from a precautionary principle perspective, to urgently re-evaluation of regional and global climate models to better acknowledge and incorporate these aerosol changes and for policymakers to prepare for scenarios where previously considered 'safe' pathways might accelerate towards dangerous climate thresholds. 

For mitigation, we advocate for policies that consider the full lifecycle impacts of emissions, including the unintended consequences of pollution control measures.