So, up to now, I could see the powerful Arctic current destroying the Gulf Stream and plunging the UK into bitter cold. This Arctic current is much heavier than other winters, although this chart has only been on my radar for two years. You have to accept my word for it, since nobody does anything with this.
But there has been massive instability in the Atlantic equatorial current or 'conveyor belt'. Again, no historical reference. Looking at it again in 3D, I can see how the cold current would plunge beneath the Gulf Stream and hit the equatorial belt.
For the warm spells, the Pacific Heat Battery builds up heat energy, and then finally gives up, for chaotic reasons. There would also be a counter force of heat build-up in the west. For all this time, the North Pacific current has been warming the Arctic, causing ice melting and the Beaufort Gyre. This gyre is another battery, but storing up cold fresh water from the ice. As being less dense in a vortex, the middle would be 2 cm higher than the rest. This would be seen in satellite gravity measurements, if somebody would look.
Then it all blows. A huge Arctic current comes down. As it hits the Gulf Stream, it plunges in very deep water that is the home of the Titanic. The current comes roaring down and hits the equatorial current, which generally goes all the way down, since it is also a heat battery.
This is a hypothesis. It could be tested by looking at the deep currents. They won't look, though. Nobody is doing this sort of thing. Everything is being handled by the Unemployed English Majors. :)