From global pandemics to widespread protests to ferocious cyclones, 2020 hasn’t been short of setbacks so far. To add to the drama, the European Space Agency (ESA), on 20th May, released a statement about the weakening of Earth’s magnetic field over a specific region. Stretching from South America to south-west Africa, the magnetic field over this region of the Atlantic Ocean is decreasing at a very rapid rate (technically speaking, this rate is called the decay rate). Although these reports were sidetracked by the vigorous flow of daily COVID-19 updates, the consequences of this phenomenon might be even more devastating.
This phenomenon is popularly known as the South Atlantic Anomaly (SAA). Before attempting to understand the exact reason for its occurrence, let’s take a refresher on the Earth’s magnetic field.
fig. 1 Earth’s cross-section
Imagine slicing the Earth into two hemispheres to obtain the cross-section shown above. The sections marked as Outer core and Inner core are together responsible for generating the magnetic field. Iron and Nickel are the major constituents of the outer core, which has a temperature ranging from 4000 to 5000 degrees Celsius. The inner core, however, is predominantly Iron, with a temperature of around 5000 to 7000 degrees Celsius. These metals tend to remain in the liquid state at these temperatures. But, an enormous amount of pressure on the inner core converts it into a solid.
As electric conductors, iron and nickel both possess a sea of electrons in the liquid outer core. Simple high school physics tells us that a moving charge creates a magnetic field around it, given by the colloquial ‘right-hand thumb rule’. Inside the Earth, the role of this “moving charge” is played by this sea of electrons. Since the inner core is much hotter than the outer core, it consistently provides heat to the inner part of the outer core. Due to this, the cooler, more dense mass displaces inwards, towards the centre, and the hotter, less dense mass moves outwards. Movement of matter induces the motion of the sea of electrons. In combination with a spiralling effect due to Earth’s rotation (known as the Coriolis effect), this motion gives rise to the magnetosphere surrounding the planet.
This magnetic field (or magnetic shield) protects the Earth from harmful Solar winds and Cosmic radiations. During processes known as solar flares and Coronal Mass Ejections (CME), the sun releases massive amounts of energy and matter. These explosions on the surface of the sun are capable of wiping out entire civilizations on Earth. The Earth’s magnetic field collides with this solar matter, deflecting it away and leading to vivid colourations we know as the Polar Lights. During a CME, the sun’s corona releases electrons and protons, which ultimately crash with the atmospheric particles, thus producing a spectacle of light.
fig. 2 The Polar Lights
In order to track the situation in the South Atlantic, the European Space Agency launched a cluster of three satellites (known as the Swarm mission) on 22nd November 2013. Scientists on Earth have used this constellation of satellites to gather data on the magnetic field levels around the globe.
fig. 3 ESA’s Swarm Constellation
Each satellite operates in its own orbit at different altitudes. Data from each satellite is obtained, combined, and interpreted to estimate the overall picture. For instance, the data from January 2014 to 2020 can be represented as follows:
fig. 4 Earth’s magnetic field level (2014 vs 2020)
The region marked in blue is known as the South Atlantic Anomaly (SAA). Evidently, the SAA has expanded over the years and moved towards the second centre in south-west Africa. Scientists believe that in a few years, the SAA might split into two different cells having separate centres of deficit. This gradual break-down raises urgent questions about the reason and the consequences that might follow.
Although the exact reason is still unknown, some scientists argue that the so-called rock continents beneath the Earth’s surface are responsible for the reduction. These rock continents are known as Large low-shear-velocity provinces (LLSVPs). Squeezed between the outer core and the mantle (see Fig. 1), these provinces extend laterally and vertically for thousands of kilometres. The African LLSVP and Pacific LLSVP are the two provinces discovered to date.
fig. 5 African and Pacific LLSVPs
Researchers argue that these large structures are interfering with the Iron present in Earth’s core responsible for creating the magnetic field. Although the hypothesis hasn’t been validated yet, we do understand the expected results of this anomaly. There are two ways this can play out. The first is that the South Atlantic Anomaly is merely a result of a disturbance in the Earth’s inner and outer core, which is not uncommon over millions of years. The second one suggests that the planet might be heading for a complete pole reversal, with devastating consequences.
Pole reversal, as the name suggests, refers to a process in which the magnetic poles exchange their places. In other words, following pole reversal, the needle of any contemporary magnetic compass will tell you that the South is somewhere near Canada while the North is in Antarctica. Earth has two pairs of poles, the magnetic north-south poles, and the geographic north-south poles. While the geographic pair remains stationary, the magnetic pair is always in motion. This motion gives rise to a complete pole reversal about 4-5 times in a million years, or once every 200-250 thousand years. The last time a pole reversal occurred was over 780 thousand years ago. Thus, a pole reversal is definitely overdue. What’s important to note is that a pole reversal doesn’t take place overnight. Even if it started right now, it would take at least a millennium before it’s complete. Since the present generation would be long gone by then, it seems there’s nothing to worry about, right?
Interestingly, the process of a pole reversal is much more catastrophic than the final result itself. During the inversion, multiple North-South magnetic poles are born inside the Earth’s surface. These numerous pairs lead to a significant decrease in the magnetic field’s intensity, thus exposing the planet to harmful radiation. If we consider the SAA to be the tipping point for pole reversal, then severe complications have already begun. The well-known Hubble Space Telescope is forced to shut down its electronic components while passing through the SAA. This means that the telescope takes no observations in that period. The reason for this is an increased amount of radiation experienced over the region. Moreover, the astronauts aboard the International Space Station have reported an increased observation of light flashes. These flashes, known in scientific circles as the Cosmic Ray Visual Phenomena, are a direct consequence of the weakening magnetic field. Apart from this, astronauts have reported malfunctions of communication systems and computers (known as single-event upsets).
The loss of the magnetic field has devastating earthly implications as well. Without the field, all man-made satellites and electrical power grids would be rendered useless, leading to a severe malfunction of the world’s technologies. Moreover, the ozone layer in the atmosphere, which is intimately related to the magnetic field, would break down. The ozone layer protects us from harmful UV radiations from the Sun, which can introduce damage to human DNA in cells. Thus, in the absence of a protective layer, the incidence of cellular damage-related diseases like cancer would skyrocket. Birds who use the magnetic field as a way of navigating would be disoriented. Pole reversal also brings along with it a number of north-south pole pairs spread randomly around the planet. This random alignment leads to a considerable reduction in magnetic field strength, thus increasing exposure to harmful UV radiations and charged particles which disrupt electrical grids and communication systems. Engineers maintaining the grids estimated that it would take 2.6 trillion dollars to fix the damage caused by the last CME in 2012, if preventive measures hadn’t been taken. These preventive measures like temporary grid-wide blackouts need to be taken in addition to the protective effect rendered by the Earth’s magnetic field. One can only imagine the damage these storms can cause with a magnetic field which is weak or absent.
The pole reversal hypothesis is backed by an event called the North Pole Shift. In recent years, the geographic North pole has been moving towards Siberia from Canada at a rather fast clip (about 25 miles per year).
fig. 6 North pole shift
But, recent studies published in the distinguished scientific journal Nature have dismissed this so-called event as a myth. This school of thought claims that it is like a simple tug-of-war game. Beneath the Earth’s surface, two competing “magnetic blobs” are continuously pulling at the magnetic north pole. One of them is below Canada, while the other is under Siberia. In the past few decades, the Siberia patch has overpowered the Canada patch because of which the North pole’s movement has begun to accelerate, thus crossing the International Date Line and moving onto the other side. It is expected that a century or two in the future, the blob under Canada will pull the North Pole towards itself, and the cycle will repeat.
While a lot of the science behind the SAA is still in the stage of conjecture and speculation, scientists are all in agreement that the Earth is up to something fishy down there. Well-founded explanations for this phenomenon would not only raise the curtains on its role in a possible pole reversal but also enable scientists and engineers to slow down this rate of decay. Until then, one must hope that the deadly repercussions do not arrive at our doorstep sooner than expected.