Cold War era nuclear tests by US and erstwhile Soviet Union changed rainfall pattern, says study

The Cold War era that had seen seen both super powers — the United States and the erstwhile Soviet Union — engaged in a nuclear weapons development under a mutual deterrence program, left behind immense impact in political and defense purview. A new study claims that it did leave its impact on how the test clouds changed the rain patterns on Earth.

One such leftover is traceable to radioactive period following nuclear bomb tests, which have changed rainfall patterns thousands of miles from the detonation sites. The study says that these nuclear bomb tests during the Cold War may have changed rainfall patterns thousands of miles from the detonation sites.

Scientists at the University of Reading have researched how the electric charge released by radiation from the test detonations, carried out predominantly by the US and Soviet Union in the 1950s and 1960s, affected rainclouds at the time.

The study, published in Physical Review Letters, examined historic records between 1962-64 from a research station in Scotland. Scientists compared days with high and low radioactively-generated charge, finding that clouds were visibly thicker, and there was 24% more rain on average on the days with more radioactivity.

Rain falling from a cloud. Photo taken in Gloucestershire CREDIT Prof Giles Harrison, University of Reading

Professor Giles Harrison, lead author and Professor of Atmospheric Physics at the University of Reading, 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.”

It has long been thought that electric charge modifies how water droplets in clouds collide and combine, potentially affecting the size of droplets and influencing rainfall, which is difficult to observe in the atmosphere. But combining the bomb test data with weather records, the scientists were able to retrospectively probe it.

The race to develop nuclear weapons was a key feature of the Cold War and detonations were carried out in remote Nevada Desert in the US, and on Pacific and Arctic islands, though radioactive pollution spread widely throughout the atmosphere. Radioactivity ionises the air, releasing electric charge. The researchers from the Universities of Reading, Bath and Bristol, studied records from Met Office research weather stations at Kew near London and Lerwick in the Shetland Isles.

The weather observatory in Lerwick, Shetland Isles, Scotland, where the historic rainfall records were taken   /  CREDIT: Dr Keri Nicoll, University of Reading and University of Bath

Located 300 miles north west of Scotland, the Shetland site was relatively unaffected by other sources of anthropogenic pollution, making it suitable for a test site to observe rainfall effects which, although likely to have occurred elsewhere too, would be much more difficult to detect.

Atmospheric electricity is most easily measured on fine days, so the Kew measurements helped to identify nearly 150 days where there was high or low charge generation over the UK while it was cloudy in Lerwick. The Shetland rainfall during the same period showed differences which vanished after the major radioactivity episode was over.

The findings, which will pioneer new research in cloud-related geoengineering and to explore how electric charge could influence rain, relieve droughts or prevent floods, without the use of chemicals.