Could ‘Cleaner’ Fuels Be Reducing Cloud Formation?
Scientists find 67% regional reduction
in cloud droplet concentration since
the introduction of ‘cleaner’ fuels
Could ‘Cleaner’ Fuels Be Reducing Cloud Formation?
by Dr. Sarah Buckland-Reynolds
Global climate models project that rainfall will decrease in most regions and across all continents (except Northern Australia) as one of the expected impacts of modern climate change. In a bid to slow down the impacts of climate change and, by extension, environmental degradation, various mitigation strategies have been devised, including switches to cleaner fuels. However, recent observations of cloud changes along newly rerouted shipping lanes around the Cape of Good Hope reveal just how counterintuitively the climate system can behave, raising important questions about whether the shift to cleaner fuels may carry unintended consequences for rainfall.
Conflict-induced ship traffic disruptions constrain cloud sensitivity to stricter marine pollution regulations (Diamond and Boss, Atmospheric Chemistry and Physics, 25 Nov 2025). In this groundbreaking analysis, researchers Diamond and Boss found that:
“∼ 80 % reduction in sulphur emissions leads to a ∼ 67 % reduction in the increase in cloud droplet number concentration per unit marine fuel oil burned.”
In what is being described as “the quintessential example of a “natural experiment” in aerosol–cloud interactions” in modern atmospheric science, researchers Diamond and Boss analyzed satellite imagery of cloud cover, tracing changes in trade routes and consequent reductions in sulphur emissions away from the Bab al-Mandab Strait due to a geopolitical crisis in the Red Sea. The magnitude of these findings uncovers important insights into the extraordinary complexity of Earth’s atmosphere, and the limits of human prediction.
Climate and Geopolitical Context of Cleaner Fuels
In January 2020, the International Maritime Organization (IMO) introduced global sulphur regulations. These regulations included limiting the sulphur used in fuel oil in the following ways:
“…the rule limits the sulphur in the fuel oil used on board ships operating outside designated emission control areas to 0.50% m/m (mass by mass) – a significant reduction from the previous limit of 3.5%. Within specific designated emission control areas, the limits were already stricter (0.10%).”
The IMO cited several co-benefits of the use of these Very/Ultra Low Sulphur Fuel Oils (VLSFOs and ULSFOs) for both the environment and health, with the impact estimated to have prevented “tens of thousands of premature deaths”. Yet risks of trade-offs were acknowledged, including the possibility of increased black carbon emissions due to incomplete combustion of low-sulphur fuels, potentially leading to dirtier soot (with higher warming potential). Despite this trade-off, advocates remained confident that the benefits outweighed the risks. Five years after the regulations took effect, estimated sulphur emissions from ships have been reduced by roughly 80%.
Unintended Atmospheric Consequences and Implications for Climate Models
Although the primary goal of the IMO 2020 sulfur cap was to improve air quality and human health, Diamond and Boss (2025) found evidence that it unintentionally altered regional cloud microphysical properties and radiative forcing, with potential implications for marine heatwave patterns.
It was already known that sulphur aerosols play a major role in cloud formation by acting as cloud condensation nuclei (CCN), enabling clouds to form with many smaller droplets. Traditionally, clouds influenced by sulphur condensation nuclei are brighter, more reflective, and often longer‑lived, producing a net cooling effect. Historically, the cumulative cooling effect attributed to aerosols, including sulphur, has masked roughly one‑third of the warming caused by greenhouse gases.
The roles of aerosols remain among the factors with the greatest uncertainty in climate models; hence, the magnitude of the impact of sulphur reductions was uncertain.
Climate prognostications cannot possibly take into account all the factors involved.
To assess the impact of the sulphur emission regulations on cloud formation, the researchers used satellite observations of Nitrogen Dioxide (NO₂) concentrations (a reliable marker of ship traffic unaffected by the rules) to confirm the roughly twofold increase in shipping around the Cape of Good Hope due to the Red Sea conflict. These ships, adhering to the new regulations, emitted significantly lower sulphur concentrations in their exhaust. Surprisingly, the researchers found that the ~80% reduction in ship fuel sulphur content dramatically reduced ships’ ability to increase cloud droplet concentrations—by approximately 67% per unit of fuel burned—rendering emissions less effective at forming cloud condensation nuclei (CCN).
Given the magnitude of the impacts on droplet numbers estimated to be less than half the climatological mean, the authors rigorously tested the statistical significance of their observations against historical records. Using what is called a Monte Carlo analysis involving 100,000 random samples from the 2003–2019 climatology, Diamond and Boss calculated the probability of observing four consecutive years (2020–2023) with “number of droplet” values (Nd values) less than half the climatological mean, as actually occurred in the data. They found that the probability of this happening randomly was less than 0.02%, confirming that the patterns found were indeed highly statistically significant. Additionally, the researchers ruled out unusual meteorology (e.g., years with high drizzle potential failing to show the expected cloud response) as an explanation. These tests strongly supported their conclusion that the post‑2020 decline in cloud sensitivity was driven by the sulphur regulations.
The implications of these dynamics may be far reaching, as cloud microphysics (Nd, droplet size, drizzle suppression, turbulent mixing) determine how much sunlight clouds reflect and how long they persist. These microphysical changes are what ultimately influence surface temperatures, regional rainfall, atmospheric stability, and cloud feedback.
The unintended consequence of this low sulphur policy highlights the complexities involved when considering optimal actions for environmental well-being. In addition to disrupting the radiative balance through reduced aerosol brightening, some low-sulphur fuel alternatives can increase black carbon emissions, introducing additional warming feedback.
Design Implications: Our Fine-tuned Atmosphere
The complexity of these dynamics underscores the profound interdependence of Earth’s atmospheric system. The authors emphasize that significant uncertainties persist in estimating radiative forcing, as it is influenced by numerous physical processes beyond changes in droplet number concentration alone. For instance, if microphysical alterations affect precipitation efficiency or turbulent mixing, the resulting radiative forcing could deviate substantially—either amplifying or dampening the effect implied by Nd-based estimates. In other words, the atmosphere responds to perturbations through nonlinear, cascading adjustments rather than straightforward cause‑and‑effect relationships.
The potential for these changes to propagate across the entire South Atlantic basin—and possibly beyond—via tightly coupled ocean-atmosphere circulation further underscores the profound interconnectivity and complexity of Earth’s climate system.
These observations raise a question frequently posed in discussions of intelligent design:
How does a planet end up with atmospheric processes so interlinked that a tiny microphysical shift can ripple across the entire climate system?
Why these Results Matter
To date, understanding how clouds respond to changes in aerosol levels remains one of the greatest challenges in climate science. As the authors pointed out in their paper, aerosol-cloud interactions are the “single largest source of uncertainty in global climate projections”. The new findings provide valuable observational constraints on cloud microphysical sensitivity, helping to refine estimates of Earth’s energy balance and inform future environmental regulations.
Building on this important new insight for model calibration, the authors considered the potential implications on global models, should these regional observations prove extrapolatable to larger scales:
“If the constraint on cloud microphysical sensitivity to shipping emissions established here could be extrapolated globally, it may provide an emergent constraint on historical radiative forcing from aerosol-cloud interactions from global climate models.”
Human Stewardship and the Power of God
The findings of Diamond and Boss teach us several lessons. While surprising, the findings do not undermine environmental action. Instead, they highlight the need for ongoing monitoring and management of policy impacts. They further highlight that responsible stewardship requires intellectual humility: recognizing that Earth’s climate operates through interconnections; we are still striving to fully grasp.
While the shift to cleaner fuels undeniably protects human health and air quality, evidence shows there is also a possibility for intended consequences to arise. These findings also further unveil the profound interconnectivity of Earth’s systems, reminding us that because all creation is interconnected, interventions must be evaluated holistically. Considering these findings, they serve as a gentle reminder to embrace humility, eschew simplistic assumptions, reverence the intricate complexity of God’s creation, and pursue faithful stewardship over domineering control.
This case study further illustrates that the hydrological cycle, often portrayed in textbooks as relatively simple, remains one of Earth’s most intricate systems. Humans can perturb it, but ultimately, we cannot command it, as Scripture reminds us.
Jeremiah captures this truth clearly:
None of the idols of the nations can send rain;
the sky by itself cannot make showers fall.
We have put our hope in you, O Lord our God,
because you are the one who does these things (Jeremiah 14:22, GNT)
As we continue to make new discoveries and strive for environmental stewardship, may we approach it all with humility: we are but students of the exquisite works crafted by our Creator God, called to exercise dominion through gentle, faithful care of the treasures He has placed in our hands.
Dr. Sarah Buckland-Reynolds is a Christian, Jamaican, Environmental Science researcher, and journal associate editor. She holds the degree of Doctor of Philosophy in Geography from the University of the West Indies (UWI), Mona with high commendation, and a postgraduate specialization in Geomatics at the Universidad del Valle, Cali, Colombia. The quality of her research activity in Environmental Science has been recognized by various awards including the 2024 Editor’s Award from the American Meteorological Society for her reviewing service in the Weather, Climate and Society Journal, the 2023 L’Oreal/UNESCO Women in Science Caribbean Award, the 2023 ICETEX International Experts Exchange Award for study in Colombia. and with her PhD research in drought management also being shortlisted in the top 10 globally for the 2023 Allianz Climate Risk Award by Munich Re Insurance, Germany. Motivated by her faith in God and zeal to positively influence society, Dr. Buckland-Reynolds is also the founder and Principal Director of Chosen to G.L.O.W. Ministries, a Jamaican charitable organization which seeks to amplify the Christian voice in the public sphere and equip more youths to know how to defend their faith.