Thursday, September 23, 2021

Magnetic Reversal?

Movement of the North Magnetic Pole over the past 120 years (source).

Marcus Wynne recently pointed me to an article,"Is Earth’s magnetic field flipping? Earth’s magnetic north pole is shifting south at speeds of 30 miles per year recently, suggesting we are on the brink of a magnetic reversal". The article relates:

    Something odd is happening to Earth’s magnetic field. Over the last 200 years, it’s been slowly weakening and shifting its magnetic north pole (where a compass points, not to be confused with the geographic north pole) from the Canadian Arctic toward Siberia.

    In recent decades, however, that slow shift south has quickened — reaching speeds upwards of 30 miles per year (48 kilometers per year). Could we be on the brink of a geomagnetic reversal, in which the magnetic north and south poles swap places?

The article goes on to explain that the magnetic field has flipped ten times in the last 2.6 million years alone, with the last occurrence 780,000 years ago. And it describes some of the problems that we may experience:

    The direct effect on mankind could be only slight, but not so for technology. We use artificial satellites for navigation, television broadcasting, weather forecasting, environmental monitoring and communication of all kinds. Without the protection of a magnetic field, these satellites could be seriously disrupted by solar wind or cosmic rays colliding with electronic circuits.

    A weak magnetic field in the South Atlantic Ocean, known as the “South Atlantic Anomaly,” already adversely affects satellites and could be an indication of what is to come.

    Recent geological studies have suggested a possible reason for the anomaly. It is widely believed that our Moon was formed when Earth was struck by the planet Theia 4.5 billion years ago, but the remains of Theia have never been found. It now appears that the remains of Theia may lie beneath our feet.

    There are two huge volumes of rock buried deep in the Earth, each one millions of times larger than Mount Everest (and expanding) and denser and hotter than the rest of Earth’s mantle. Scientists suggest that these rock masses are the missing remains of Theia and that they interfere with the convection of molten iron — giving rise to the weak magnetic field in the South Atlantic.

Not discussed in the article, but the huge structures also mean that the Earth's mass is not distributed evenly, meaning that the Earth could act as a spinning asymmetrical object that could quickly flip--the Dzhanibekov effect

    In any event, although there are the long term flips discussed in the article, there are flips and disruptions of a shorter nature. A 2017 article at The Conversation, "Why the Earth’s magnetic poles could be about to swap places – and how it would affect us," relates:

    Geomagnetic reversals occur a few times every million years on average. However, the interval between reversals is very irregular and can range up to tens of millions of years.

    There can also be temporary and incomplete reversals, known as events and excursions, in which the magnetic poles move away from the geographic poles – perhaps even crossing the equator – before returning back to their original locations. The last full reversal, the Brunhes-Matuyama, occurred around 780,000 years ago. A temporary reversal, the Laschamp event, occurred around 41,000 years ago. It lasted less than 1,000 years with the actual change of polarity lasting around 250 years.

Geomagnetic excursions are more frequent but, because of their short duration, harder to detect in the geological records. Although the Laschamp excursion is the best known and best studied, there are many others believed to have occurred including the Mono Lake excursion of 28,000 years ago, and at least 12 or 15 since the Brunshes-Matuyama reversal (see PDF here, p. 377). As you will note from the aforementioned source, these excursions appear to be fairly regular. Moreover, more recent data suggests that there have been more excursions and that these excursions can occur every 12,000 years, with the last associated with the Younger Dryas event 12,000 years ago.

    But back to The Conversation's article. It also discusses the possible impacts, stating:

    The alteration in the magnetic field during a reversal will weaken its shielding effect, allowing heightened levels of radiation on and above the Earth’s surface. Were this to happen today, the increase in charged particles reaching the Earth would result in increased risks for satellites, aviation, and ground-based electrical infrastructure. Geomagnetic storms, driven by the interaction of anomalously large eruptions of solar energy with our magnetic field, give us a foretaste of what we can expect with a weakened magnetic shield.

    In 2003, the so-called Halloween storm caused local electricity-grid blackouts in Sweden, required the rerouting of flights to avoid communication blackout and radiation risk, and disrupted satellites and communication systems. But this storm was minor in comparison with other storms of the recent past, such as the 1859 Carrington event, which caused aurorae as far south as the Caribbean.

    The impact of a major storm on today’s electronic infrastructure is not fully known. Of course any time spent without electricity, heating, air conditioning, GPS or internet would have a major impact; widespread blackouts could result in economic disruption measuring in tens of billions of dollars a day.

    In terms of life on Earth and the direct impact of a reversal on our species we cannot definitively predict what will happen as modern humans did not exist at the time of the last full reversal. Several studies have tried to link past reversals with mass extinctions – suggesting some reversals and episodes of extended volcanism could be driven by a common cause. However, there is no evidence of any impending cataclysmic volcanism and so we would only likely have to contend with the electromagnetic impact if the field does reverse relatively soon.

    We do know that many animal species have some form of magnetoreception that enables them to sense the Earth’s magnetic field. They may use this to assist in long-distance navigation during migration. But it is unclear what impact a reversal might have on such species. What is clear is that early humans did manage to live through the Laschamp event and life itself has survived the hundreds of full reversals evidenced in the geologic record.

    Earth Sky Magazine also has an interesting article on the shifting magnetic pole. It notes:

    Since Earth’s magnetic field is created by its moving, molten iron core, its poles aren’t stationary and they wander independently of one another. In fact, since its first formal discovery in 1831, the north magnetic pole has travelled over 1,240 miles (2,000 km) from the Boothia Peninsula in the far north of Canada to high in the Arctic Sea. This wandering has generally been quite slow, around 9km (6 mi) a year, allowing scientists to easily keep track of its position. But since the turn of the century, this speed has increased to 30 miles (50 km) a year. The south magnetic pole is also moving, though at a much slower rate (6-9 miles, or 10-15 km a year).

    This rapid wandering of the north magnetic pole has caused some problems for scientists and navigators alike. Computer models of where the north magnetic pole might be in the future have become seriously outdated, making accurate compass-based navigation difficult. Although GPS does work, it can sometimes be unreliable in the polar regions. In fact, the pole is moving so quickly that scientists responsible for mapping the Earth’s magnetic field were recently forced to update their model much earlier than expected.

2 comments:

  1. When we were living in Fairbanks, they predicted there wouldn't be an aurora (visible from there) by now. Of course that didn't pan out . . .

    ReplyDelete
    Replies
    1. If the magnetic field wasn't weakening, they might have been correct. But with a weakening magnetic field, we might see auroras visible far south of normal during solar storms.

      Delete

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