"When scientists mapped the Earth's magnetic field down to the level of the outer-core, they discovered that under the South Atlantic Anomaly the simple north-south divide we know at the surface had broken down. There are patches where the field has actually flipped and points north instead of south.

Using his weather analogy, Lathrop believes "a particularly violent or unusual patch of weather" in the molten metal of the outer-core is responsible for reversing the field.

If these patches continue to deepen and spread, the entire Earth's magnetic field could reach a tipping point and flip, he believes.

It is not something that would happen overnight - it could take thousands of years, during which period the field would be pretty confused.

The magnetic poles could wander to the equator for example, and take with them the spectacular Northern Lights. It would not be out of character - the shifting flows of the core have reversed Earth's field hundreds of times before.

"It's not a question of if the Earth is going to reverse the magnetic field, but when," says Lathrop."