03/02/2026
When we talk about climate change, carbon dioxide, methane, and other heat-trapping gases immediately come to mind. Yet there’s another family of particles – tiny, volatile, and largely forgotten – that played a major role decades ago: aerosols.
These microscopic particles, whether solid or liquid or of natural or human origin, hang suspended in the atmosphere. They arise naturally from wildfires, volcanic eruptions, and ocean spray, but also from human activities like spray cans, fossil fuel combustion, and industrial processes. Their influence on climate is complex, powerful, and deeply uncertain.
Aerosols affect Earth’s energy balance through two primary mechanisms:
Direct Effect: depending on their composition, particles can either reflect sunlight back into space (causing cooling) or absorb it (causing warming). Sulfates, for instance, reflect light, while black carbon absorbs it.
Indirect Effect: aerosols serve as cloud condensation nuclei. By increasing the number of droplets in a cloud, they make clouds smaller, brighter, and longer-lasting, boosting solar reflection and cooling the planet. But this can also disrupt precipitation patterns with unpredictable consequences. These interactions represent one of the greatest sources of uncertainty in quantifying human-caused climate change.
The “masking” of warming
While greenhouse gases drive direct, well-quantified warming, aerosols typically mask a portion of that warming and alter regional temperature and precipitation patterns. The extent of this “masking” remains one of climate science’s biggest unknowns, despite extensive research by the Intergovernmental Panel on Climate Change (IPCC) and the World Meteorological Organization (WMO).
What we know and what we don’t
Some aspects are well established. We know that human activity has increased concentrations of industrial and combustion-related aerosols, which collectively exert a cooling effect that has partially offset greenhouse gas warming in recent decades.
Natural aerosols, such as desert dust and volcanic ash, also affect radiation and ecosystems at various scales. Saharan dust storms, for example, reach the Atlantic Ocean carrying nutrients and particles that impact both atmospheric and marine systems.
Yet major uncertainties persist. A critical question is: how much hidden warming will surface once aerosol emissions decline? Cleaning up air quality will clear the atmosphere, but it may also reveal warming that has been partially suppressed. The magnitude and speed of this effect remain difficult to predict, as the European Geosciences Union cautions.
Current research
Today, extensive observations, experiments, and models are advancing our understanding of aerosols and their climate interactions. In Spain, the Barcelona Supercomputing Center (BSC) runs a sophisticated program analyzing these particles and their atmospheric roles. Globally, institutions coordinate complementary initiatives:
- Satellites: missions like MODIS, CALIPSO, and the EU’s Copernicus program provide global maps of aerosol concentration, size, and vertical profiles.
- Ground-based networks: the AERONET photometer network precisely measures aerosol columns, validating satellite data and feeding into models.
- Aircraft campaigns: research flights and field laboratories evaluate essential physical and chemical processes governing aerosol-cloud interactions.
- Climate models: data comparison and assimilation help reduce uncertainty, though results still vary depending on how aerosol-cloud interactions are represented.
To narrow these uncertainties, the scientific community is pushing for more integrated global observation, combining satellite and ground networks, improving algorithms, and standardizing measurements. A flagship effort is the International Cooperative for Aerosol Prediction (ICAP), a forum bringing together forecast centers, remote sensing data providers, and leading system developers to share best practices and tackle urgent challenges.
Field campaigns targeting specific regions are also being launched to study aerosol-cloud processes, along with coupled models that integrate observations to diagnose and reduce biases in climate representations. While scientific publications point to significant progress, uncertainties remain far from resolved.
The health-climate dilemma
Ultimately, aerosols present a scientific and political tension: reducing them improves public health and protects ecosystems, yet it may also accelerate warming previously buffered by their cooling effect.
According to the IPCC and the World Health Organization, which in 2021 issued guidelines on recommended aerosol particle limits, the solution is not to delay air quality improvements, but to pair them with rapid, deep cuts in greenhouse gas emissions. Enhanced observation and research are essential to anticipate and manage regional climate effects. Because the climate system’s fragility demands integrated policy: cleaner air, less carbon, and, above all, more science.
