The battered sign outside the disused nuclear power plant in PennsylvaniaA US state with a population of nearly 13 million. tells a terrifying story. "On 28 March, 1979, and for several days thereafter - as a result of technical malfunctions and human error - Three Mile Island's Unit 2 Nuclear Generating Plant was the scene of the nation's worst commercial nuclear accident.

"Radiation was released, a part of the nuclear core was damaged, and thousands of residents evacuated the area."

Once the plant was shut down, most people assumed it was gone for ever. But a few weeks ago came the news that it was to reopen in 2028 - to power Microsoft's centres for storing data.

In March, Amazon announced that it was buying a nuclear-powered data centre, also in Pennsylvania. Last month Google said that it had signed a deal to use small nuclear reactors.

Data centres need a huge amount of electricity both to operate their computers and to cool them down. Their energy consumption is forecast to more than double by 2030, thanks to the demands of AI.¹ An AI-powered internet search is reckoned to use 10 times as much power as an ordinary one.²

Ireland, the Netherlands and Singapore have all halted data-centre development because of the effect on the national gridIn the UK, the network of power stations, power lines and electricity infrastructure that brings electricity to buildings. . In 2023 the centres were responsible for 21% of Ireland's electricity usage; their consumption has risen by 400% since 2015.³

Meanwhile, tech companies are under pressure to cut carbon emissions. Nuclear power is seen as a way of generating extra electricity cleanly, despite the risks involved and radioactive waste created.

In an article for The Guardian Chris Stokel-Walker set about trying to work out how much data the average person uses, and their resulting carbon footprintThe total amount of greenhouse gases (including carbon dioxide and methane) that are generated by our actions. China is the top emitter with 28% of the world's total emissions. The US is second with 14%..

"All those emails and videos and games don't just appear on our screens by magic," he wrote. "Everything we do digitally involves the vast transfer of data... Everything on the internet, every link you click, every video you watch, is physically stored in a data centre somewhere."

According to Stokel-Walker, the carbon dioxide emissions generated by sending just one email are around 17g. A 2020 analysis by the International Energy Agency (IEA) found that watching an hour of Netflix was equivalent in emissions terms to boiling a kettle, producing about 36g of CO₂.

An estimate by Zero Waste Scotland suggests all our online activity generates an average of 8.62kg of CO₂ a week (about 448kg a year), which is equivalent to travelling about 30 miles in an average-sized petrol car.

According to the UK's Department of Transport, the average car produces 0.2kg of carbon emissions per mile. Making 50 searches on Google every day for a year, would produce the same emissions as driving for 39 miles; playing Fortnite for an hour a day for a year would be equivalent to driving for at least 71 miles; but streaming an HD film for an hour a day for a year would produce the same emissions as driving for 4,745 miles.

Stokel-Walker's conclusion is that we need to be mindful about everything we do in the digital world. His advice is "think twice, text once."

Should we go on data diets?

Yes: It is mad to use as much data as we do when we are supposed to be reducing the world's energy consumption. Nuclear power may be a clean source of electricity, but it is not always safe.  

No: The amount of data that we use as individuals is tiny compared to the demands of governments and big business. Sending fewer texts or emails will not make any difference to anything.

Or... If AI becomes as clever as its inventors think it can, it will recognise that its massive energy use is a threat to the environment and turn itself off without humans having to make a decision.