For years, scientists believed that human industrial activity was the primary driver of airborne particles that help form clouds.
These tiny cloud-seeding particles play a crucial role in regulating Earth’s temperature by reflecting sunlight away from the surface.
But recent findings from the CLOUD experiment at CERN challenge this assumption, revealing a natural process that could reshape our understanding of climate regulation.
A study conducted by a team of around 80 scientists suggests that the pre-industrial atmosphere was far from particle-deficient.
In fact, trees may have been producing significantly more cloud-seeding particles than previously estimated.
If this finding holds true, it could mean that Earth’s clouds have always been more reflective than we thought—potentially altering our models of past and future climate change.
Why Do Cloud Particles Matter?
Clouds play a vital role in Earth’s climate by reflecting sunlight back into space.
The more cloud droplets a cloud contains, the brighter and more reflective it becomes, leading to a cooling effect on the planet.
These droplets form around tiny airborne particles, or aerosols, which act as cloud “seeds.”
In today’s world, about half of these cloud-forming particles come from natural sources like sea spray, volcanic eruptions, and wildfires.
The other half is largely produced by human activity—most notably from burning fossil fuels.
This process releases sulfur dioxide, which eventually transforms into sulfuric acid—a key ingredient in forming cloud-seeding aerosols.
For decades, scientists assumed that sulfuric acid was a necessary component for cloud formation.
But the CERN study suggests otherwise: certain organic compounds released by trees can also form cloud-seeding particles, potentially compensating for the reduction in human-made aerosols as air pollution decreases.
A Major Assumption Turned on Its Head
For years, climate models have predicted that pre-industrial skies contained far fewer particles than today’s atmosphere.
This assumption has played a significant role in estimates of past global temperatures and the role of clouds in climate regulation.
But the CLOUD experiment’s latest results throw this into question.
Using a sophisticated stainless-steel simulation chamber, scientists recreated atmospheric conditions from centuries ago, measuring how various gases interact to form cloud-seeding particles.
Their findings were surprising: organic gases emitted by trees (terpenes) can independently create cloud-forming particles, without the need for industrial pollutants like sulfuric acid.
This means that Earth’s atmosphere before industrialization might have contained far more cloud-forming particles than previously assumed.
If so, pre-industrial clouds would have been brighter and more reflective than we thought, leading to a naturally cooler climate.
What This Means for Climate Change Predictions
If the pre-industrial world was already more reflective than scientists previously believed, this could mean that past climate models have been overestimating the cooling effect of pollution on modern temperatures.
This could have significant implications for future warming projections.
Key takeaway: If natural processes have always played a larger role in cloud formation than previously assumed, the reduction of human-made pollution may not cause as dramatic a warming effect as feared.
Can Trees Help Offset Climate Change?
There is growing concern that as air pollution is reduced worldwide, fewer human-made particles will be available to seed clouds, reducing their ability to reflect sunlight and causing temperatures to rise more quickly.
However, if trees naturally produce more of these cloud-forming particles than expected, they may help counteract some of this effect.
While reducing greenhouse gas emissions remains critical, this research suggests that nature might have built-in climate-regulating mechanisms that we are only beginning to understand.
As pollution decreases, natural compounds from trees may step in to replace lost cloud-seeding particles, helping to mitigate rising global temperatures.
The Need for Further Research
While this study provides strong evidence that the pre-industrial atmosphere contained more cloud-forming particles than previously estimated, there is still much to uncover.
Climate scientists will need to adjust existing models to account for these newly discovered natural processes and reassess how they factor into long-term climate predictions.
One thing is certain: nature’s role in cloud formation is far more complex than we once believed.
As research continues, we may find that the planet has more self-regulating mechanisms than previously assumed—offering new hope in the fight against climate change.
