Earth's magnetic field - the force that protects us from deadly radiation bursts
from outer space - is weakening dramatically.
Scientists have discovered that its strength has dropped precipitously over
the past two centuries and could disappear over the next 1,000 years.
The effects could be catastrophic. Powerful radiation bursts, which normally
never touch the atmosphere, would heat up its upper layers, triggering climatic
disruption. Navigation and communication satellites, Earth's eyes and ears, would
be destroyed and migrating animals left unable to navigate.
'Earth's magnetic field has disappeared many times before - as a prelude to
our magnetic poles flipping over, when north becomes south and vice versa,' said
Dr Alan Thomson of the British Geological Survey in Edinburgh.
'Reversals happen every 250,000 years or so, and as there has not been one
for almost a million years, we are due one soon.'
For more than 100 years, scientists have noted the strength of Earth's magnetic
field has been declining, but have disagreed about interpretations. Some said
its drop was a precursor to reversal, others argued it merely indicated some temporary
variation in field strength has been occurring.
But now Gauthier Hulot of the Paris Geophysical Institute has discovered Earth's
magnetic field seems to be disappearing most alarmingly near the poles, a clear
sign that a flip may soon take place.
Using satellite measurements of field variations over the past 20 years, Hulot
plotted the currents of molten iron that generate Earth's magnetism deep underground
and spotted huge whorls near the poles.
Hulot believes these vortices rotate in a direction that reinforces a reverse
magnetic field, and as they grow and proliferate these eddies will weaken the
dominant field: the first steps toward a new polarity, he says.
And as Scientific American reports this week, this interpretation has now been
backed up by computer simulation studies.
How long a reversal might last is a matter of scientific controversy, however.
Records of past events, embedded in iron minerals in ancient lava beds, show some
can last for thousands of years - during which time the planet will have been
exposed to batterings from solar radiation. On the other hand, other researchers
say some flips may have lasted only a few weeks.
Exactly what will happen when Earth's magnetic field disappears prior to its
re-emergence in a reversed orientation is also difficult to assess. Compasses
would point to the wrong pole - a minor inconvenience. More importantly, low-orbiting
satellites would be exposed to electromagnetic batterings, wrecking them.
In addition, many species of migrating animals and birds - from swallows to
wildebeests - rely on innate abilities to track Earth's magnetic field. Their
fates are impossible to gauge.
As to humans, our greatest risk would come from intense solar radiation bursts.
Normally these are contained by the planet's magnetic field in space. However,
if it disappears, particle storms will start to batter the atmosphere.
'These solar particles can have profound effects,' said Dr Paul Murdin, of
the Institute of Astronomy, Cambridge. 'On Mars, when its magnetic field failed
permanently billions of years ago, it led to its atmosphere being boiled off.
On Earth, it will heat up the upper atmosphere and send ripples round the world
with enormous, unpredictable effects on the climate.'
It is unlikely that humans could do much. Burrowing thousands of miles into
solid rock to set things right would stretch the technological prowess of our
descendants to bursting point, though such limitations do not worry film scriptwriters.
Paramount's latest sci-fi thriller, The Core - directed by Englishman Jon Amiel,
and starring Hilary Swank and Aaron Eckhart - depicts a world beset by just such
a polar reversal, with radiation sweeping the planet.
The solution, according to the film, to be released next year, involves scientists
drilling into Earth's mantle to set off a nuclear blast that will halt the reversal.
Given that temperatures at such depths rival those of the Sun's surface, such
a task would seem impossible - except, of course, in Hollywood.
© Guardian Newspapers Limited 2002