"Bob" wrote in message ...


Will the NAD slowly weaken over many years, or is there
historical evidence that it can shut down fast ?


From what I understand, it can shut down *very* fast.
Perhaps within a decade or so. And indeed can start
up again within a similar timescale.
These climate 'flips' from one steady state to another,
within a matter of a few years, are one of the most
important findings of the behaviour of our climate when it
had been hitherto assumed that such changes took place
gradually over hundreds or even thousands of years.

Col
--
Bolton, Lancashire.
160m asl.