New Delhi: For decades, vast blankets of white clouds drifting over the world’s oceans have quietly helped keep the planet cool. But scientists now warn that this natural cooling system may be weakening faster than previously thought, potentially accelerating global warming.
A new study by researchers from California Institute of Technology (Caltech) and Google has found that low-level clouds—often described as Earth’s natural sunshade—become thinner as carbon dioxide (CO2) concentrations increase, allowing more solar energy to reach the planet’s surface.
The findings suggest that climate change could reinforce itself through a process known as cloud feedback, making future warming more severe than previously estimated.
What Are Low-Level Clouds?
Low-level clouds form at altitudes of up to around 2,000 metres (6,500 feet) above Earth’s surface and are most commonly found over the oceans, where evaporation supplies abundant moisture.
They include three main cloud types:
- Stratus, which form broad, flat layers and often produce light drizzle.
- Stratocumulus, widespread cloud sheets that cover large areas of the sky.
- Cumulus, recognisable by their flat bases and rounded tops, which can develop into towering storm clouds under favourable conditions.
These clouds reflect a significant proportion of incoming sunlight back into space, reducing the amount of heat absorbed by Earth’s surface. Scientists often compare them to a layer of natural sunscreen protecting the planet from excessive warming.
Why Are Scientists Seeing Fewer Clouds?
The researchers identified three main factors behind the decline in low-level cloud cover.
The first is a reduction in aerosols—tiny airborne particles produced by sources such as industrial activity and vehicle emissions. Aerosols help water droplets form around them, making cloud formation easier. Cleaner air resulting from stricter pollution controls has reduced aerosol concentrations in many regions.
The second factor is rising greenhouse gas concentrations. Higher levels of carbon dioxide warm the atmosphere and, in some areas, make it drier, conditions under which clouds are less likely to persist.
The third is the warming of the ocean surface, which alters atmospheric circulation and moisture patterns, affecting cloud formation.
Together, these changes create what climate scientists call cloud feedback: fewer clouds allow more sunlight to warm the oceans, which in turn further reduces cloud formation.
What Did The Study Find?
The study was led by Zhaoyi Shen of Caltech, who said one of the biggest uncertainties in climate science has been how low-level clouds respond to rising temperatures.
According to the research, cloud cover thins rapidly as atmospheric CO2 levels increase, indicating that Earth’s climate may respond more strongly to greenhouse gas emissions than many earlier models suggested.
Co-author Tapio Schneider, a Caltech professor who also works at Google, said the findings confirm that cloud feedback is a measurable process that amplifies warming rather than offsetting it.
Thousands Of Simulations Powered By AI Hardware
To reach their conclusions, the researchers carried out 7,083 high-resolution climate simulations—their largest modelling effort to date.
Using weather observations from the US National Oceanic and Atmospheric Administration (NOAA), they analysed 500 locations across the tropical Pacific Ocean during four different seasons, separately examining the effects of rising temperatures and increasing carbon dioxide levels.
The simulations were powered by Google’s Tensor Processing Unit (TPU) chips, specialised hardware developed for artificial intelligence.
According to Yi-Fan Chen, Engineering Director at Google, the project demonstrates how AI computing infrastructure can support large-scale scientific research beyond machine learning.
What Could This Mean For The Future?
The findings build on earlier research suggesting that low-level cloud cover has been declining globally for more than two decades.
A previous study led by Paolo Ceppi of Imperial College London found evidence that low cloud cover has been decreasing worldwide since 2003. Another study published in 2024 suggested that this trend may be contributing to the recent acceleration in global warming.
If cloud cover continues to diminish, scientists warn that Earth’s natural cooling capacity could weaken further, potentially increasing the pace of climate change.
The researchers say the publicly available simulation data could also help scientists better understand ancient warm periods, such as the Eocene epoch, when atmospheric carbon dioxide concentrations were roughly four times today’s levels.
The dataset is already being used by the CliMA research collaboration, involving scientists from Caltech and the Massachusetts Institute of Technology (MIT), to develop AI-powered climate models aimed at improving future weather and climate forecasts.
