Cold War Nuclear Bomb Tests Altered Rainfall Patterns Thousands of Miles Away

Nuclear tests carried out during the Cold War appear to have altered patterns of rainfall thousands of miles from the detonation sites, scientists have discovered. By looking at historical records from a remote research station in Scotland, a team of researchers showed radioactivity from the bombs increased the amount of rain by 24 percent.

The scientists, led by Giles Harrison, from the U.K.'s University of Reading, say the discovery could have implications for geoengineering research by providing a better understanding of the processes that govern rainfall.

Rain occurs when water droplets that form clouds get too large and heavy. This process is also influenced by the droplet charge.

"It's long been known that electric charges influence the behaviour of water droplets, and in particular how droplets stick or collide with each other," Harrison told Newsweek. "Droplets colliding is an important aspect of how small droplets grow to become raindrops, but whether the charge can ultimately influence rainfall is very difficult to prove."

To investigate, Harrison and colleagues looked at how nuclear bomb tests carried out in the 1950s and 60s may have influenced rainfall patterns. Radioactivity is known to release charges into the air through ionisation. If the charge is attached to water droplets in clouds, it changes the way they stick together and eventually grow into raindrops.

Thousands of nuclear tests have been carried out since the first bomb was dropped on Hiroshima in 1945. According to Reuters, the U.S. has detonated 1,127, while the Soviet Union has performed 726 tests.

In their study, published in Physical Review Letters, the researchers looked at rainfall in the Shetland Islands, Scotland, between 1962 and 1964—a period when nuclear tests were being carried out. This island is far from other sources of pollution, so any large changes to rainfall patterns could be attributed to radioactivity released from the bombs. "Studying rainfall observations during this period allowed us to see if the charge had weather-related effects," Harrison said.

Their findings showed increased rainfall coincided with increased radioactivity. On days there were high levels of charge from radioactivity, the clouds were thicker and there was around 24 percent more rain.

This, the team say, provides evidence that electric charge affects rainfall—a finding that could prove useful for geoengineering research in the future. Geoengineering is the idea that we could artificially manipulate natural processes to prevent or limit climate change. Projects range from wide-scale tree planting in order to remove carbon from the atmosphere, to firing aerosols into the atmosphere to reflect sunlight before it reaches Earth's surface.

Discussing how the findings could be used, Harrison said: "In principle it is possible to release charge artificially, and indeed some experiments have done this on small scales, mostly from the surface. A possible benefit of releasing charge is that it is relatively easily and simply generated, and would not leave residues as conventional cloud seeding does.

"However, very thorough understanding of the atmosphere is needed before such activities can be reliably contemplated, as the atmospheric processes are complicated and there can be many unexpected consequences. The findings offer a step forward for this, in bounding how much charge might be needed.

"Releasing radioactivity is definitely not being suggested here. Should there be a useful application to geoengineering, there are other ways of releasing atmospheric charge, and in a targeted way, such as by using aircraft."