Sorry for the overly dramatic title, but I thought it was a good idea to talk about magnetic field reversals. The latest article I have read was this one by Reuters, discussing an impending magnetic field reversal. The scientists they interviewed suggest it could be coming, as the Earth’s field had moved 1500 km during the past 100 years, and has weakened by 10%. They suggest that the loss of the Earth’s magnetic field could cause all kind of chaos, from the loss of protection of satellites in orbit, to impacts on life itself from harmful cosmic particles. They then cite the fact that the lack of magnetic field is the reason Mars does not have life, as the lack of it caused the atmosphere to be exposed to the stripping effects of the solar wind (all the while ignoring that Venus lacks a magnetic field, but has a dense atmosphere that would crush anyone should they dare to step out for a walk).
I won’t deny that it would be a challenge to protect satellites from being bombarded by the solar plasma, and it would probably cause chaos in our electrical grids. We have already seen what happens when massive solar storms hit the Earth. Back on March 13, 1989, the entire power grid of the Canadian province of Quebec was disabled when a solar storm overloaded the infrastructure. The entire power infrastructure in North America barely coped when such a large area became disabled. During the same event, satellites and the Space Shuttle Discovery noticed strange anomalies in their electrical systems. The cause of the disturbances at the surface is geomagnetically induced currents, which flow along the surface of the earth. The image below comes from the Space Weather Canada website, illustrating the various effects that the solar wind can have on man-made infrastructure. Just to note, my honours project (way back in 2004-2005!) focused on collecting magnetotelluric data that would be used for assessing the hazards of geomagnetically induced currents in Canada, but that will be a story for another day.
So, will the lack of a magnetic field cause some sort of Armageddon? No doubt, if the magnetic field did dissipate, a lot of infrastructure that we use every day would be at risk. This could cause a lot of social strife, should a large solar storm knock it out. But would lifeforms themselves be at risk? I think the answer to this question is no. Let’s first look at the history of the magnetic field during the past 5 million years:
During the past 5 million there have been many magnetic field reversals (black stands for “normal” polarity – the same as today, while white is reversed). The last magnetic reversal happened 780,000 years ago. The timing of reversals does not follow any apparent pattern. I found this figure published in a paper in 2005 on the magnetic field strength in the lead up and after the magnetic field reversal:
In the paper, they note that the field weakens progressively for 60,000 to 80,000 years before the reversal, then quickly rebounds afterwards. At no point is there evidence that the field intensity drops to zero, at least not at the 1000 year sampling interval that they used. As a comparison, here is the magnetic field intensity for the past 7000 years, using data from dated lake sediment:
If you compare the graphs, even though the magnetic field declining in strength at the present, it is still has very high intensity compared with the time preceding most of the reversal events. I don’t think a reversal is imminent, despite what people might say. Even if it is in decline, it would probably take thousands of years before a reversal happens, and the magnetic field won’t even completely disappear.
There have been some people who have linked a weakened magnetic field to the demise of Neanderthals. The authors suggest that a weakened magnetic field would reduce the amount of ozone in the ozone layer, and cause more intense UV-B radiation to reach the surface, causing a higher incidence of cancer, thus hastening their demise. Although extra UV radiation due to ozone depletion can cause problems (just look at the skin cancer rates in Australia), I think it would be a bit of a stretch to say that it could cause an extinction. The link between solar variability (which is modulated by the intensity of the Earth’s magnetic field) and climate change remains tenuous at best.
In conclusion, I think that it is irresponsible for people to say that the reversal is “overdue”, and that it will cause all sort of chaos for life on earth (aside from possible effects to infrastructure). A geomagnetic reversal does not appear to be imminent, and links of magnetic field intensity and climate/extinction events is at present very weak. Even if the field were to reverse, the magnetic field is not going to disappear completely, and even if it did, we still have a thick atmosphere to protect us from a lot of the sun’s harmful radiation. We humans are a resourceful species, we will most definitely find a way to cope.