Earth’s Magnetic Field May Change Faster Than We Thought — New Research

 In Space

This arti­cle was orig­i­nal­ly pub­lished at The Conversation. The pub­li­ca­tion con­tributed the arti­cle to Space.com’s Expert Voices: Op-Ed & Insights.

Christopher Davies, Associate pro­fes­sor, University of Leeds

The Earth’s mag­net­ic field, gen­er­at­ed 3,000km below our feet in the liquid iron core, is cru­cial­ly impor­tant to life on our planet. It extends out into space, wrap­ping us in an elec­tro­mag­net­ic blan­ket that shields the atmos­phere and satel­lites from solar radi­a­tion.

Yet the mag­net­ic field is constantly changing in both its strength and direction and has under­gone some dra­mat­ic shifts in the past. This includes enig­mat­ic rever­sals of the mag­net­ic poles, with the south pole becom­ing the north pole and vice versa.

A long-stand­ing ques­tion has been how fast the field can change. Our new study, published in Nature Communications, has uncov­ered some answers.

Rapid changes of the mag­net­ic field are of great inter­est because they rep­re­sent the most extreme behav­ior of the ocean of molten iron in the liquid core. By tying the observed changes to core process­es, we can learn impor­tant infor­ma­tion about an oth­er­wise inac­ces­si­ble region of our planet.

Read more: Why the Earth's magnetic poles could be about to swap places – and how it would affect us

Historically, the fastest changes in Earth’s mag­net­ic field have been associated with reversals, which occur at irreg­u­lar inter­vals a few times every mil­lion years. But we dis­cov­ered field changes that are much faster and more recent than any of the data asso­ci­at­ed with actual rever­sals.

Magnetic reversal of Earth's poles.  (Image credit: NASA)

Nowadays satel­lites help mon­i­tor changes in the field in both space and time, com­ple­ment­ed by nav­i­ga­tion­al records and ground-based obser­va­to­ries. This infor­ma­tion reveals that changes in the modern field are rather pon­der­ous, around a tenth of a degree per year. But, while we know that the field has exist­ed for at least 3.5 bil­lion years, we don’t know much about its behav­ior prior to 400 years ago.

To track the ancient field, sci­en­tists ana­lyze the mag­net­ism record­ed by sed­i­ments, lava flows and human-made arti­facts. That’s because these mate­ri­als con­tain micro­scop­ic mag­net­ic grains that record the sig­na­ture of Earth’s field at the time they cooled (for lavas) or were added to the land­mass (for sed­i­ments). Sediment records from cen­tral Italy around the time of the last polar­i­ty rever­sal almost 800,000 years ago suggest relatively rapid field changes reach­ing one degree per year.

Such mea­sure­ments, how­ev­er, are extreme­ly chal­leng­ing, with results still being debated. For exam­ple, there are uncer­tain­ties in the process by which sed­i­ments acquire their mag­net­ism.

Improved measurements

Our research takes a dif­fer­ent approach by using com­put­er models based on the physics of the field gen­er­a­tion process. This is com­bined with a recent­ly pub­lished recon­struc­tion of global vari­a­tions in Earth’s mag­net­ic field span­ning the last 100,000 years, based on a com­pi­la­tion of mea­sure­ments from sed­i­ments, lavas and arti­facts.

This shows that changes in the direc­tion of Earth’s magnetic field reached rates that are up to ten degrees per year – ten times larger than the fastest cur­rent­ly report­ed vari­a­tions.

The fastest observed changes in the geo­mag­net­ic field direc­tion occurred around 39,000 years ago. This shift was asso­ci­at­ed with a local­ly weak field in a con­fined region just off the west coast of Central America. The event fol­lowed the global “Laschamp excursion” – a “failed rever­sal” of the Earth’s mag­net­ic field around 41,000 years ago in which the mag­net­ic poles briefly moved far from the geo­graph­ic poles before return­ing.

The fastest changes appear to be asso­ci­at­ed with local weak­en­ing of the mag­net­ic field. Our model sug­gests this is caused by the move­ment of patch­es of the intense mag­net­ic field across the sur­face of the liquid core. These patch­es are more preva­lent at lower lat­i­tudes, sug­gest­ing that future search­es for rapid changes in direc­tion should focus on these areas.

The impact on society

Changes in the mag­net­ic field, such as reversals, prob­a­bly don’t pose a threat to life. Humans did manage to live through the dra­mat­ic Laschamp excur­sion. Today, the threat is mainly down to our reliance on elec­tron­ic infra­struc­ture. Space weath­er events such as geo­mag­net­ic storms, aris­ing from the inter­ac­tion between the mag­net­ic field and incom­ing solar radi­a­tion, could dis­rupt satel­lite com­mu­ni­ca­tions, GPS and power grids.

Satellites are at risk from space weather. (Image credit: Andrey Armyagov/Shutterstock)

This is trou­bling – the eco­nom­ic cost of a col­lapse of the US power grid due to a space-weather event has been esti­mat­ed at around one tril­lion dol­lars. The threat is seri­ous enough for space weath­er to appear as a high pri­or­i­ty on the UK nation­al risk reg­is­ter.

Space weath­er events tend to be more preva­lent in regions where the mag­net­ic field is weak — some­thing we know can happen when the field is chang­ing rapid­ly. Unfortunately, com­put­er sim­u­la­tions sug­gest that direc­tion­al changes arise after the field strength begins to weaken, mean­ing we cannot pre­dict dips in field strength by just mon­i­tor­ing the field direc­tion. Future work using more advanced sim­u­la­tions can shed more light on this issue.

Is anoth­er rapid change in the mag­net­ic field on its way? This is very hard to answer. The fastest changes are also the rarest events: for exam­ple, the changes iden­ti­fied around the Laschamp excur­sion are over two times faster than any other changes occur­ring over the last 100,000 years.

This makes it dif­fi­cult for sci­en­tists to pre­dict rapid changes — they are “black swan events” that come as a sur­prise and have a big impact. One pos­si­ble route for­ward is to use physics-based models of how the field behaves as part of the fore­cast.

We still have a lot to learn about the “speed limit” of Earth’s mag­net­ic field. Rapid changes have not yet been direct­ly observed during a polar­i­ty rever­sal, but they should be expect­ed since the field is thought to become glob­al­ly weak at these times.

This arti­cle is repub­lished from The Conversation under a Creative Commons license. Read the original article.

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