evidence: Earth’s magnetic poles could start to flip. What happens then? [...] For a polarity reversal to occur, the magnetic field needs to weaken by about 90% to a threshold level. This process can take thousands of years, and during this time, the lack of a protective magnetic shield around our planet allows more cosmic rays – high-energy particles from elsewhere in the universe – to hit us. [...] ‘In some simulations you see features like the SAA growing during a pole reversal,’ he said. ‘It’s not necessarily the case, but it wouldn’t be a surprise if something like this was involved in a magnetic reversal.’