Nuclear bombs detonated during the Cold War caused atmospheric changes that increased rainfall thousands of miles away, research has found.
The electrical charge released by radiation from atomic tests carried out mainly by the United States and the Soviet Union in the 1960s led to increased rainfall over Shetland.
Scientists studied historical records from a research station in Scotland to compare days with high and low radioactivity, and found clouds were visibly thicker and there was 24% more rain on average the days with more radioactivity.
Giles Harrison, professor of atmospheric physics at the University of Reading and lead author of the study, said: “In studying the radioactivity released by Cold War weapons testing, scientists of the time discovered the atmospheric circulation patterns. We have now reused this data to examine the effect on precipitation.
“The politically charged atmosphere of the Cold War led to a nuclear arms race and global anxiety. Decades later, this global cloud has produced a silver lining by giving us a unique way to study how electrical charge affects rain.
During the Cold War arms race, atomic tests were carried out in places such as the Nevada desert in the United States and on islands in the Pacific and Arctic. Despite their remoteness, radioactive pollution has spread widely through the atmosphere.
Radioactivity ionizes the air releasing an electrical charge. Scientists have long believed that this charge changes the way water droplets in clouds combine, potentially affecting droplet size and influencing precipitation, but this is difficult to observe in the atmosphere.
In the study, published in Physical Review Letters, researchers from the universities of Reading, Bath and Bristol combined bomb test data with records from Met Office weather stations in Kew, London and Lerwick in Shetland.
Due to Lerwick’s isolation over 100 miles northwest of mainland Scotland, it is a good site to observe the potential radiation related effects of rainfall as it is relatively unaffected by other sources of anthropogenic pollution.
Atmospheric electricity is difficult to measure on cloudy days, so measurements from Kew – generally sunnier than Lerwick – were used to identify almost 150 days when there was high or low charge generation above over Great Britain.
The results will help show the typical loads possible in natural, non-thunderstorm clouds. Scientists think it could help cloud-related geoengineering research, which explores how electric charge influences rain, and could potentially be used to relieve droughts.
Harrison is leading a project studying electrical effects on dust and clouds in the United Arab Emirates as part of the national “rain enhancement science” program.