The Jet-Stream which wiggles its way sinusoidally round the top half of the planet, traditionally has looped over the top of Scotland during what we expect to be Summer, leaving us in a high pressure bubble of warm air.
For the last few years, especially last year, it spends long periods stalled out of phase with its historic track and instead of sitting in a protected bubble, shielded from the procession of Atlantic Fronts, we've lain directly under the stream, receiving week after week after week of low-pressure weather systems, none particularly fierce by the time they reach us (they all start as hurricanes or tropical storms down in the Caribbean), but due to the higher temperature of the Atlantic from Global Warming, they do carry enormous amounts of moisture with them, so the rain is heavy and last year almost constant.
The same phase-shift which leaves us wet, also affects every other time-zone with unseasonal weather, places expecting rain get none and those expecting sun end up with inshore rescue boats deployed.
It's all to do with the Arctic Sea Ice melting and the albedo of the region decreasing, accelerating the local temperature rise.
That all affects the routing of the Jet Stream.
Scariest of all is the prospect that the decreased salinity from all the melted fresh-water ice of the Greenland glaciers will stop the Gulf Stream from sinking and returning to the Caribbean as a cold water sub-surface current.
If the Atlantic Conveyor is "switched off" in this way, the UK will no longer sit bathed in its warmth and we'll start to get winters more in keeping with our latitude, which is North of Peter.
Canada and the northern states of the US are used to coping but we don't have the infrastructure to handle Arctic winters, so years of chaos and misery will ensue.