Scientists are grappling with changes in clouds around the world, their shifting nature posing one of the greatest challenges to understanding our warming planet, according to a report by French news agency AFP.
Cloud behaviour is notoriously difficult to predict, but scientists know clouds play a vital role in warming and cooling the Earth. As some clouds rise higher (trapping more heat in the atmosphere), while others reflect less sunlight or shrink (allowing more solar energy to reach the surface), it’s clear that such changes are having an impact on the climate.
Recent research demonstrates how a lack of clouds drove a surge in record-breaking global heat over the last two years. What is less clear is how clouds may change as the climate continues to warm, and what effect those changes will have on warming and to what degree.
“That’s why clouds are the greatest challenge. Figuring them out is – and has been – the big roadblock,” Bjorn Stevens, director of Climate Physics at the Max Planck Institute for Meteorology in Germany, told AFP.
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Robin Hogan, principal scientist at the European Centre for Medium-Range Weather Forecasts, told the agency that, as clouds change, the same amount of heat-trapping greenhouse gas emissions could cause much more warming – or much less. “That’s a big scientific uncertainty.” Advances in technology are enabling better modelling, allowing scientists to fill in the gaps and have a better understanding of what’s to come.
Part of the difficulty is that cloud behaviour depends on their type, structure and altitude. Fluffy, low-hanging clouds tend to have a cooling effect, their size and brightness blocking and reflecting incoming sunlight before it can hit the Earth’s surface. Higher, streaky clouds tend to have the opposite effect: allowing sunlight in, then trapping it in the atmosphere when it reflects back. As the climate has warmed, certain clouds have drifted higher in the atmosphere, amplifying warming. But there’s also growing evidence that lower clouds are declining and becoming less reflective.
Shifting behaviour isn’t the only issue, though. Clouds form around aerosols, tiny airborne particles like dust or sand – or pollution from human activity, including the burning of fossil fuels. A shift to low-sulphur shipping fuel back in 2020 provides the clearest example yet of how efforts to tackle air pollution may have the unintended effect of accelerating warming by sharply reducing cloud cover and brightness.
Richard Allan, a climate science professor at the UK’s University of Reading, reflected on which of these factors might be responsible for the unprecedented warming seen in 2023 in a recent interview with Science Daily. He said we need to understand which ones explain the “remarkable global dimming” seen that year, in order to “understand how much global warming will occur and how fast.”
