Radiation from atomic bomb tests carried out during the Cold War may have led to changes in rainfall patterns in the UK, scientists have found.
Research suggests detonations carried out in remote areas during the 1950s and 1960s resulted in changes to weather, in locations thousands of miles away.
The Cold War lasted from 1947 until 1991, and was a period of heightened tension between the East and the West, with widespread fears of a full-blown nuclear war.
A team of researchers from the universities of Reading, Bath and Bristol looked at historic rainfall records between 1962 and 1964 from research stations in London and Scotland.
They found clouds were "visibly thicker" and there was "24% more rain on average" on the days when there was more radioactivity in the Shetland Isles.
Giles Harrison, a professor of atmospheric physics at the University of Reading and lead author on the study, said: "By studying the radioactivity released from Cold War weapons tests, scientists at the time learnt about atmospheric circulation patterns.
"We have now reused this data to examine the effect on rainfall.
"Decades later, that global cloud [of the Cold War] has yielded a silver lining, in giving us a unique way to study how electric charge affects rain," he continued.
Radioactivity can arise from an emission of radiation originating from a nuclear reaction.
It can lead to an increase in air conductivity in the atmosphere through a process known as ionisation, releasing electric charge.
Scientists have long suspected electric charge in the air can affect the way water droplets combine in the clouds which, in turn, can influence rainfall.
However, these changes have been difficult to observe from modern-day weather data.
The research team combined bomb test data with historical weather records, gathered from stations at Kew near London and Lerwick in the Shetland Isles.
Scientists believe learning more about how electric charge affects rainfall will improve understanding of the weather processes and could help relieve droughts or prevent floods.
The findings are published in the journal Physical Review Letters.
Cover image: A raincloud with the River Severn in the foreground, taken from western edge of Cotswolds (Picture: Giles Harrison, University of Reading, 2020).