The next Carrington Event

Written by Roger Andrews

On Energy Matters we’ve discussed at length the potential for blackouts resulting from the closure of fossil fuel plants. There is, however, another potential cause of blackouts that we haven’t addressed – solar storms, or more accurately coronal mass ejections (CMEs). Experts disagree as to the likely impacts of a major CME, with estimates ranging from a few days of power outages affecting a comparatively small number of people to months or even years of outages affecting hundreds of millions.

All we can be certain of is that the Earth will sooner or later be impacted by another major CME, and probably sooner rather than later because major CMEs occur about once every 150 years and the last one – the Carrington Event – occurred 158 years ago.

On September 1 and 2, 1859, the Earth was struck by a major CME that has become known as the “Carrington Event” after the astronomer who observed its formation on the surface of the sun.

Figure 1: Sunspots of September 1, 1859, as sketched by Richard Carrington. A and B mark the initial positions of an intensely bright event, which moved over the course of five minutes to C and D before disappearing.

The Carrington Event caused an aurora that was visible as far south as the tropics and bright enough to allow people in the Northeast US to read newspapers by its light at night. Miners in the Rocky Mountains started cooking breakfast in the middle of the night, thinking that day had arrived. It also brought down the rudimentary telegraph system of the day:

Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks. Telegraph pylons threw sparks. Some telegraph operators could continue to send and receive messages despite having disconnected their power supplies.

The question is, what would happen if another Carrington-sized CME hit the Earth now?

First, what is a CME? According to NASA:

Coronal mass ejections (CMEs) are huge explosions of magnetic field and plasma from the Sun’s corona. When CMEs impact the Earth’s magnetosphere they are responsible for geomagnetic storms and enhanced aurora …. CMEs travel outward from the Sun typically at speeds of about 300 kilometers per second, but can be as slow as 100 kilometers per second or faster than 3000 kilometers per second. The fastest CMEs erupt from large sunspot active regions, powered by the strongest magnetic field concentrations on the Sun. These fast CMEs can reach Earth in as little as 14-17 hours. Slower CMEs, typically the quiet region filament eruptions, take several days to traverse the distance from the sun to Earth. Because CMEs have an embedded magnetic field that is stronger than the background field of the solar wind, they will expand in size as they propagate outward from the Sun. By the time they reach the Earth, they can be so large they will fill half the volume of space between the Sun and the Earth. Because of their immense size, slower CMEs can take as long as 24 to 36 hours to pass over the Earth, once the leading edge has arrived.

Figure 2: The leading edge of a CME impacts the Earth’s magnetic field

Because of the way CMEs (which consist mostly of high energy protons and X-rays) interact with the Earth’s magnetic field their impacts tend be greatest at geomagnetic latitudes of between 40 and 60 degrees. Except for Southeast Australia, New Zealand and the southern tip of Africa the Southern Hemisphere is almost all ocean at these latitudes (Figure 3), but in the Northern Hemisphere the latitude band includes most of the industrial centers of the US and Northern Europe. (Although CME impacts are not confined to higher latitudes. The “Halloween” solar storm of 2003 reportedly damaged 15 transformers in South Africa.)

Figure 3: Geomagnetic vs. geographic latitudes

CMEs damage electrical grids and equipment by inducing currents in the ground and in power lines, blowing out transformers and other equipment. Power lines are most vulnerable in regions where they are long and where the ground is poorly conducting. CMEs can also do serious damage to aircraft navigation systems, satellites and communications, but these impacts are not considered here.

And have CMEs caused blackouts in the past? Indeed yes. The “March 1989 superstorm” blacked out the entire province of Quebec for 9 hours. As reported in the 2015 UK space weather preparedness strategy report:

During this storm, a large solar magnetic impulse caused a voltage depression on the Hydro-Quebec power system in Canada that could not be mitigated by automatic voltage compensation equipment. The failure of the equipment resulted in a voltage collapse. Specifically, five transmission lines from James Bay were tripped, which caused a generation loss of 9,450 MW. With a load of about 21,350 MW, the system was unable to withstand the generation loss and collapsed within seconds. The province of Quebec was blacked out for approximately 9 hours.

It’s also reported that the 1989 CME came close to shutting down grids in the Northeast US. It certainly fried some transformers there:

Figure 4: Damage done to a transformer in New Jersey by the March 1989 “solar superstorm”

As reported by the US National Academy of Sciences the “Halloween storms” of October 19 through November 7 2003 caused an hour-long blackout in Sweden as well as affecting spacecraft, satellite systems, communications and air traffic:

The Sydkraft utility group in Sweden reported that strong geomagnetically induced currents (GIC) over Northern Europe caused transformer problems and even a system failure and subsequent blackout.

The CME of May 1921, which was ten times stronger than the 1989 storm, also brought down telegraph systems in the US and Europe but did not cause any blackouts, reportedly because of the lack of connectivity in the electrical grids of the day.

But all three of these CMEs were significantly less intense than the 1859 Carrington Event. So what might a Carrington-sized CME do? No one knows for sure. Predicted impacts are necessarily based on assumptions and computer models and as might be expected with analyses of this type range from minor to catastrophic. Falling in the latter category is a 2008 study by Kappenman:

…. an estimate of $1 trillion to $2 trillion during the first year alone was given for the societal and economic costs of a “severe geomagnetic storm scenario” with recovery times of 4 to 10 years.

Figure 5 shows Kappenman’s assessment of the areas of the US vulnerable to system collapse during a major CME (outlined in black). According to the caption “the impacts would be of unprecedented scale and involve populations in excess of 130 million”:

Figure 5: Areas vulnerable to system collapse during a major CME impacting at 50 degrees geomagnetic latitude, outlined in black

Kappenman also predicted that the disruptions caused by a large CME could last for a year or more, with the reason being that the high-voltage transformers that are particularly vulnerable to damage during solar storms are not available off-the-shelf; they have to be manufactured. And how many of them are there in the US? Three hundred and sixty-five, according to Kappenman’s Figure 7.2:

Figure 6: Location of at-risk extra-high-voltage transformers

And that’s just the US. The impacts on Canada and Europe would presumably be comparable.

A 2013 study that evaluated the potential impacts of a major CME on the US power grid prepared by Atmospheric and Environmental Research for Lloyd’s of London lowered Kappenman’s estimate of 130 million to 20-40 million people affected but was in general agreement with his other conclusions:

The total U.S. population at risk of extended power outage from a Carrington-level storm is between 20-40 million, with durations of 16 days to 1-2 years. The duration of outages will depend largely on the availability of spare replacement transformers. If new transformers need to be ordered, the lead-time is likely to be a minimum of five months. The total economic cost for such a scenario is estimated at $0.6-2.6 trillion USD.

An assessment of potential CME impacts over a range of scenarios is given in a January 2017 study by Oughton et al entitled Quantifying the daily economic impact of extreme space weather due to failure in electricity transmission infrastructure. It concludes:

Extreme space weather due to coronal mass ejections has the potential to cause considerable disruption to the global economy by damaging the transformers required to operate electricity transmission infrastructure. However, expert opinion is split between the potential outcome being one of a temporary regional blackout and of a more prolonged event. The temporary blackout scenario proposed by some is expected to last the length of the disturbance, with normal operations resuming after a couple of days. On the other hand, others have predicted widespread equipment damage with blackout scenarios lasting months.

The article is of limited value partly because it is now paywalled and partly because it concentrates on estimating daily financial losses without specifying how many days the losses continue for. The four scenarios it considers nevertheless define a range of possible CME impacts. The scenarios are:

A solar storm within:

  • 55° ± 2.75° geomagnetic latitude (S1)
  • 50° ± 2.75° geomagnetic latitude (S2)
  • 45° ± 2.75° geomagnetic latitude (S3)
  • 50° ± 7.75° geomagnetic latitude (S4)

The regions of the US that get blacked out in each scenario are plotted in Figure 7:

Figure 7: US “blackout zones” (red) for Oughton et al’s four CME scenarios

S4, which affects 66% of the US population, or over 200 million people, emerges as the worst case because the CME is assumed to impact 15.5 degrees of latitude rather than the 5.5 degrees impacted by the other three scenarios. The key question is how long might this huge area be blacked out for? A few days might be tolerable, even with economic losses estimated at close to $50 billion/day. But black-starting the grid over an area of this size would be challenging even if there were no damage to equipment, and impossible if a large number of transformers had burned out. It is in fact likely that a blackout of S4 dimensions would lead to a breakdown of society if it went on long enough.

Which brings up the question, what can be done to mitigate CME impacts? One option is to install protective equipment. As the Lloyd’s study noted:

…. several steps can be taken to harden the electric grid against geomagnetically induced currents: neutral-current-blocking capacitors can be installed to block GIC from flowing into at-risk transformers, series-line capacitors can be installed on autotransformers, improvements can be made to the tripping techniques to avoid false tripping from GIC harmonics, and the utilisation of GIC monitors at transformers will ensure that current levels remain stable.

On the other hand, as the National Academy of Science’s 2008 Severe Space Weather Workshop pointed out, grid-protection measures are being offset by ever-increasing grid vulnerability:

Electric power grids ….. continue to become more vulnerable to disruption from geomagnetic storms. For example, the evolution of open access on the transmission system has fostered the transport of large amounts of energy across the power system in order to maximize the economic benefit of delivering the lowest-cost energy to areas of demand. The magnitude of power transfers has grown, and the risk is that the increased level of transfers, coupled with multiple equipment failures, could worsen the impacts of a storm event.

The only completely fail-safe solution is in fact to shut grids down altogether before the CME strikes, but this would be politically unthinkable and also impossible to implement given that there would probably be less than a day’s warning that a major CME was on its way.

All of which leaves us with this intriguing and I think valid question:

Which poses the greater threat to civilization, man-made climate change or the next Carrington Event?

I was going to write something on this but got lazy and decided to solicit the views of the readership instead.

Finally it should be noted that a Carrington-sized CME narrowly missed the Earth on July 23, 2012. “If it had hit,” said Daniel Baker of the University of Colorado two years later, “we would still be picking up the pieces.”


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