Pollution makes thunderstorms worse by creating bigger, longer lasting clouds and cooling temperatures with their shadows, say scientists.
Computer simulations of cloud data from the western Pacific, south eastern China and Oklahoma showed pollution increased their size, thickness and duration.
Taking a closer look at the properties of water droplets and ice crystals within, the researchers found pollution resulted in smaller droplets and ice crystals regardless of location.
In clean skies ice particles were heavier and fell faster causing the clouds to dissipate. But in polluted skies they were smaller and too light to drop leading to the larger clouds.
Dr Jiwen Fan, of Pacific Northwest National Laboratory in Washington, said: ‘This study reconciles what we see in real life to what computer models show us.
‘Observations consistently show taller and bigger anvil-shaped clouds in storm systems with pollution.’
A polluted sky has many more aerosols – natural and manmade particles – making more but smaller cloud droplets.
Researchers have long believed smaller droplets start a chain reaction that leads to bigger, longer-lasting clouds.
Instead of raining down, the lighter droplets carry their water higher, where they freeze. The freezing squeezes out the heat the droplets carry with them and causes the thunder cloud to become draftier.
Dr Fan said: ‘Modelling the details of cloud microphysical properties is very computationally intensive so models don’t usually include them.’
Polluted clouds have an effect on temperatures, with afternoon thunderstorms lasting long into the night rather than dissipating and trapping heat like a blanket.
In the day the clouds’ shadows diminish sunlight penetration and so keep the Earth cooler.
Accounting for pollution effects on storm clouds could affect the ultimate amount of warming predicted for the earth in the next few decades.
Accurately representing clouds in climate models is key to improving the accuracy of predicted changes to the climate.