"For those of you who are interested in statistics, this is a five-sigma event. So it's five standard deviations beyond the mean. Which means that if nothing had changed, we'd expect to see a winter like this about once every 7.5 million years.
[...]
She fears a further change in the balance could trigger a tipping point from where it's difficult to reverse the trajectory. "We might end up in a new state," she said. "That would be quite concerning to the sustainability of human conditions on Earth, I suspect.
Most complex random things follow a normal distribution. These have a mean (average value), and standard deviation (how spread out from the mean it is). If you get some measurement of your random thing, you can tell how likely that was by checking how many standard deviations away from the mean it is.
Within one standard deviation - happens 68% of the time
Within two standard deviations - happens 95% of the time
Within three standard deviations - happens 99.7% of the time
Within four standard deviations - happens 99.993% of the time
Within five standard deviations - happens 99.99994% of the time
Within six standard deviations - happens 99.9999998% of the time
Five standard deviations is the threshold where even particle physicists will say, "Yeah bullshit that happened at random, something else is going on here."
It's a shame the American media makes no effort to explain this stuff and instead they idiotically use vague phrases and adjectives.
[Edit: Of course - they usually entirely ignore stuff like this.]