"NORTH", as we noted yesterday, is an elusive concept. As Alexander Pope remarked:
Ask where's the North? At
York, `tis on the Tweed,
In Scotland, at the Orcades;
and there,
At Greenland, Zembla or the
Lord knows where.
The magnetic North Pole, unlike its geographical counterpart, does not remain fixed in one spot, but drifts gradually with the passing years.
These days it is close to a thousand miles "off position", lying near the northern coast of Canada, but we have reason to believe that centuries ago it may have been in the Pacific Ocean near to the island of Guam.
With the passage of time, it drifted to the mainland of Asia, passing near to the location of the present city of Shanghai, and by AD 1300 it seems to have been somewhere near to North Korea. It then followed a long slow circular path across Siberia, passing under Iceland on its way to Canada.
A consequence of this meandering of the pole is that the magnetic declination, the angle between "true" north and "magnetic" north, is continually changing. When first scientifically measured in these parts around AD 1540 it was easterly at about 8 degrees.
The easterly variation gradually declined to reach zero around 1700, and then the now westerly declination increased to reach a maximum of 24 degrees about a century later. Since 1800 or thereabouts, this westerly declination has gradually decreased to its present value of about 7 degrees.
Geological evidence, however, suggests that the Earth's magnetic field has undergone even more dramatic changes over the millenniums. Every 500,000 years or so, it seems, the system "flips" and, over a relatively short period - short in geologic time, at any rate - the magnetic field undergoes complete reversal: the north magnetic pole becomes the south, and vice versa.
The last time this happened was about three quarters of a million years ago, so the inference is that a "flip" is overdue. Some scientists have been bold enough to predict that it will occur about 2,000 years from now, and have speculated on the interesting navigational problems likely to be encountered by those fish, birds and other animals that use the Earth's magnetic field to get their bearings.
Others, however, suggest that even though such a change might be sudden on a geologic timescale, it would be gradual say over 1,000 years or so - in terms of animal and human life. Any organisms still around in AD 4000 will have ample time to become acclimatised.