LONDON-This sounds like the plot for a disaster movie: an invisible magnetic force-field that defends life on Earth against killer rays from space goes awry. Blasts of radiation destroy our satellite communications and bring the world’s electricity supplies crashing down.

Chaos reigns. Human cancer cases multiply as unshielded radiation from the sun devastates people’s DNA. Billions of creatures the world over die because their ability to migrate becomes fatally confused by changes in our planet’s magnetic field.

Ultimately, Earth’s atmosphere itself could be blown away by fierce solar winds, as happened long ago to our sister planet Mars when its magnetic field dissipated. But hold the popcorn. This is not a sci-fi movie. Leading scientists warn that this may really happen, because of an imminent revolution at the Earth’s core.

High-tech monitoring equipment is showing multiple signs that the Earth’s magnetic poles are about to flip, thanks to changes in the swirling iron core at the heart of our planet.

If this happens, Earth’s magnetic field will literally turn upside down.

During the thousand years it will take for this change to complete, our vital protective magnetic shield will become significantly weaker — with potentially disastrous consequences.

Scientists predict that it could wither to as little as a tenth of its usual force, radically diminishing Earth’s defence against radiation and streams of charged energy particles called the solar wind. Evidence from ancient rocks indicates that this reversal in the world’s magnetic field has occurred hundreds of times in our planet’s long history. Beneath Earth’s solid crust is a rolling layer of liquid iron kept molten by heat escaping from the planet’s core. The swirling currents of this mass of metal act as a gigantic electromagnet.

This creates a force field that expands tens of thousands of miles into space and acts as an energy shield against viciously powerful radiation from the sun. All life on Earth depends on this shield. Without it, solar rays would simply rip apart the fragile DNA that creates animals and plants. These liquid-iron currents beneath our feet are not stable.

Over millennia the electromagnetic field they create can completely reverse itself.

The process is believed to take several centuries — an age in human terms, but the blink of an eye in cosmic time. Evidence indicates that the next reversal is already under way. Earth’s magnetic shield is currently weakening ten times faster than previously thought, at 5 per cent per decade, according to satellite data gathered by the European Space Agency (ESA).

The magnetic field is particularly weakening over South America, an area that scientists call the South Atlantic anomaly. Satellites flying over this area have already had their circuits frazzled by localised radiation spikes.

Data from ESA monitoring has also revealed ‘restless activity’ in the liquid iron currents beneath Earth’s surface, which suggests the field could be about to flip. Scientists such as Daniel Baker, director of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, warn that if signs of a reversal are correct, areas of the planet may become ‘uninhabitable’. This is not least because Earth’s weakened magnetic field will allow powerful blasts of magnetic radiation to knock out electrical power-supply grids worldwide and fry the communications satellites that nowadays are used to regulate them. Three years ago, Earth experienced a shock mini-preview of the type of damage that might occur if Earth’s shield, called the magnetosphere, continues to weaken.

When it happened, few outside the scientific community realised its import. In 2015, a massive two-hour ‘superstorm’ of galactic cosmic rays — caused by a huge solar flare from our sun — forced temporary cracks in the magnetosphere.

Immensely high-energy radiation, which shoots through space at nearly the speed of light, triggered a severe geomagnetic storm in our atmosphere that blacked out radio signals in the parts of North and South America that are closest to the poles.

A year later, a study of satellite data by scientists at the Tata Institute of Fundamental Research in India discovered the burst of cosmic rays had pushed back Earth’s magnetic shield. The shield shrank back from its normal size of 11 times the radius of the Earth to only four times. The solar blast also prised open weak spots, temporarily, allowing destructive radiation through.

‘This indicates a transient weakening of Earth’s magnetic shield,’ the scientists warned in the authoritative journal, Physical Review Letters. ‘Future superstorms could cripple modern technological infrastructure on Earth and endanger the lives of the astronauts in space.’ Historically, Earth’s North and South magnetic poles have flipped every 200,000 or 300,000 years. The next flip is overdue — because magnetic fingerprints in ancient volcanic rocks reveal that the last one was some 780,000 years ago.

Back then, our sparsely scattered ancestors were just learning to make fire. The fossil record does not tell us how their lives were affected, but they survived. But the next magnetic shift will confront civilisation with a wholly new challenge. For nowadays the Earth’s teeming human population depends on a vast technological web of infrastructure to ensure its daily survival. But none of the systems that ensure our life-giving supplies of power and water has been built to withstand being blasted by cosmic rays.

The delicate fabric of our global civilisation could be torn asunder by the onslaught, leaving us without phones, computers, transport, heating or food.

The danger has been highlighted by Alanna Mitchell, author of a new book The Spinning Magnet: The Electromagnetic Force That Created The Modern World And Could Destroy It.

Mitchell warns: ‘The consequences for the electrical and electronic infrastructure that runs modern civilisation will be dire.’

She explains: ‘The satellite timing systems that govern electric grids would be likely to fail.

‘The grid’s transformers could be torched. Because grids are so tightly coupled with each other, failure would race across the globe, causing a domino run of blackouts that could last for decades.’

Richard Holme, the professor of earth, ocean and ecological sciences at Liverpool University, has concerns similar to Mitchell’s: ‘This is a serious business,’ he told the Mail. ‘Imagine for a moment your electrical power supply was knocked out for a few months — very little works without electricity these days.’

The survivors of such a global catastrophe would face another peril as they foraged among civilisation’s wreckage for food, warmth and water. Radiation levels could soar as though there had been a nuclear catastrophe.

Some estimates suggest that during the polar flip, our overall exposure to cosmic radiation would double. As a result, researchers predict that 100,000 people could die every year from diseases such as cancer.

Experts are divided as to whether we really will face such catastrophe, however. Officials at NASA say that while the magnetic shield may well weaken, they predict the resulting increase in solar radiation on Earth would only be ‘small — but nothing deadly’.

The agency adds: ‘Moreover, even with a weakened magnetic field, Earth’s thick atmosphere also offers protection against the sun’s incoming particles.’

Professor Holme also thinks that any radiation rises will be relatively slight — ‘much less than lying on the beach in Florida for a day. So if it happened, the protection method would probably be to wear a big floppy hat’.