Cold War atomic bomb tests in Nevada changed rainfall patterns in the UK - thousands of miles away from their detonation sites

Atomic bomb tests in the US during the Cold War changed rainfall patterns thousands of miles away in the Shetland Islands, a new study has found.

Researchers from the University of Reading studied Sheltand rainfall data from between 1962 and 1964, and compared days when there was known to have been a nuclear bomb test in the Nevada desert with those when there wasn't.

The Shetland Islands, located 300 miles north west of Scotland, were chosen because the weather there is generally 'unaffected by other man-made pollution'. 

They found that clouds were visibly thicker, with 24 per cent more rainfall, on days when there were high levels of radioactive charge in the atmosphere caused by the nuclear tests.

Lead author Giles Harrison said the findings can help scientists develop geoengineering projects that could deliver more rainfall to drought-hit areas.  

Nuclear bomb tests in the US during the Cold War changed rainfall patterns thousands of miles away in the Shetland Islands, a new study found
The weather observatory in Lerwick, Shetland Isles, Scotland, where the historic rainfall records were taken. During 'radioactive episodes' after tests in Nevada and elsewhere there was a 24 per cent increase in rainfall measured over Lerwick
The weather observatory in Lerwick, Shetland Isles, Scotland, where the historic rainfall records were taken. During 'radioactive episodes' after tests in Nevada and elsewhere there was a 24 per cent increase in rainfall measured over Lerwick
The race to develop nuclear weapons was a key feature of the Cold War, as the world's superpowers sought to demonstrate their military capabilities after WW2.
Although detonations were carried out in remote parts of the world, such as the Nevada Desert in the US, radioactive pollution spread throughout the atmosphere.
The idea that this radioactive pollution affects cloud formation has been around since the 1950s, but this study is the first to look at its impact on rainfall patterns. 
'The politically charged atmosphere of the Cold War led to a nuclear arms race and worldwide anxiety,' said Harrison.
'Decades later, that global cloud has yielded a silver lining, in giving us a unique way to study how electric charge affects rain.'
Researchers from the University of Reading studied Sheltand rainfall data from between 1962 and 1964, and compared days when there was known to have been a nuclear bomb test in the Nevada desert with those when there wasn't.
Researchers from the University of Reading studied Sheltand rainfall data from between 1962 and 1964, and compared days when there was known to have been a nuclear bomb test in the Nevada desert with those when there wasn't.
It is thought that radioactivity ionises the air resulting in an electric charge, which in turn affects the size of water droplets and influences how they collide and combine. 
However, these changes are difficult to observe in modern-day weather data, which is why the team turned to the radioactive legacy of the Cold War arms race. 
'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,' Harrison said. 
By combining the bomb test data with weather records, the scientists were able to prove their theory correct. 
The Reading team studied records from Met Office research weather stations at Kew near London and Lerwick in the Shetland Isles. 
Atmospheric electricity is most easily measured on fine days, so the Kew measurements were used 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 on these days showed differences which vanished after the major radioactivity episode was over.  
By learning more about how electrical charge affects non-thunderstorm clouds, it is thought that scientists will develop a better understanding of weather processes.

Extra rainfall is caused by increasing electric charge in clouds 

Radioactive pollution from an atomic bomb test in Nevada goes into the atmosphere and spreads 
This ionises the air and in turn releases an electric charge that makes clouds thicker
This charge then attaches to the water droplets in the clouds
These tiny droplets are more likely to attract and collide when charged, and so they combine and grow in size
Eventually becoming too heavy to stay in the cloud and they fall as raindrops 
Thee Reading team studied records from Met Office research weather stations at Kew near London and Lerwick in the Shetland Isles - they say the change in patterns would be global but are more obvious in the Shetland Isles due to it being relatively isolated with good monitoring
Thee Reading team studied records from Met Office research weather stations at Kew near London and Lerwick in the Shetland Isles - they say the change in patterns would be global but are more obvious in the Shetland Isles due to it being relatively isolated with good monitoring
The findings may be helpful for cloud-related geoengineering research, which is exploring how electric charge could influence rain, relieve droughts or prevent floods, without the use of chemicals.
In fact Professor Harrison is working with a team from the United Arab Emirates on a project using drones to deliver electric charge to clouds and cause rain to fall in desert areas.
At the moment chemicals are added to clouds to produce rainfall but they leave a residue behind - this would be a natural process. 

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