The probability of a solar storm striking Earth in the next
decade with enough force to do serious damage to electricity
networks could be as high as 12 percent, according to solar
One such storm erupted from the surface of the Sun two years
ago, on July 23, 2012. If it had been directed at this
planet, it would have produced the worst geomagnetic storm in
more than four centuries and caused extensive power problems.
Fortunately, on this occasion, the eruption pointed away from
Earth and the storm blasted safely out into space.
But if it had occurred just a week earlier, when the site was
pointed directly at our planet, billions of tonnes of highly
charged particles would have raced towards Earth's magnetic
field at a speed of 2500 km per second.
The result would have been a spectacular display of the
northern lights (aurora borealis) and southern lights (aurora
australis) visible as far as the equator, turning the night
sky as bright as daytime.
But it could also have fried the world's electricity grids
and left hundreds of millions of customers without power for
months or even years.
In the event of an eruption directed at Earth, politicians
and power grid operators would have just a few hours from the
first signs until the full fury of the storm hit to protect
the electrical systems on which modern life depends.
"The July 2012 solar storm was a shot across the bows for
policymakers and space weather professionals," US solar
researchers warned in the journal Space Weather ("A major
solar eruptive event in July 2012: defining extreme space
weather scenarios", October 2013).
"Our advanced technological society was very fortunate,
indeed, that the solar storm did not occur just a week or so
earlier. Had the storm occurred in mid-July the Earth would
have been directly targeted ... and an unprecedentedly large
space weather event would have resulted."
"There is a legitimate question of whether our society would
still be picking up the pieces," they concluded.
THE NEXT BIG ONE
Scientists and power grid operators remain divided over how
much damage the power grid would suffer in a severe solar
storm aimed directly at Earth.
A moderately severe geomagnetic storm aimed at the United
States could cut power to 130 million people and damage more
than 350 high-voltage transformers, which would take months
to replace, according to a report published by the US
National Academy of Sciences in 2008.
A really severe storm could inflict damage and disruption
estimated at between $US1 trillion and $US2 trillion, 20
times the cost of Hurricane Katrina, with a full recovery
time between four and 10 years, the academy wrote ("Severe
space weather events: understanding societal and economic
"The loss of electricity would ripple across the social
infrastructure with water distribution affected within
several hours; perishable foods and medications lost in 12-24
hours; loss of heating/air conditioning, sewage disposal,
phone service, fuel re-supply and so on," according to a
study funded by the U.S. government.
Older electrical transformers would be at particular risk of
being damaged by the enormous electrical currents induced in
the power grid by a severe storm.
Transformers cannot just be ordered from a store. Spare units
are in limited supply. Ordinarily, it takes up to 15 months
to order, manufacture, install and test a high-voltage
transformer - even longer for some specialised equipment.
"The need to suddenly replace a large number of them has not
been previously contemplated," the U.S. government's Oak
Ridge National Laboratory warned in 2010 ("Geomagnetic storms
and their impacts on the U.S. power grid", January 2010).
The problem is not just manufacturing. High-voltage
transformers are exceptionally large and heavy, so they have
to move slowly by ship, road and rail, and cannot be air
freighted. Moving one even a few kilometres requires weeks of
"It may take one week to move a 250,000-volt transformer a
short distance in major metropolitan areas," Oak Ridge
explained. "Even the distance of a few miles may take an
entire weekend, as a number of traffic lights have to be
removed and reinstated as the load is moved at snail's pace
in special trailers and the route taken has to be fully
surveyed for load-bearing capability by civil engineers."
Grid operators are more sanguine about the risks. Severe
geomagnetic storms are more likely to cause blackouts and
short-term power loss, rather than permanent damage,
according to a report prepared by the North American Electric
Reliability Corporation (NERC) on behalf of the industry
("Effects of geomagnetic disturbances on the bulk power
system", February 2012).
NERC thinks a severe storm would heat up a fully loaded
transformer to around 120 degrees Celsius for roughly four
minutes, well below the 200-degree design threshold used for
modern equipment. A really severe storm could push
temperatures over 200 degrees for 14 minutes, potentially
causing failures, but is unprecedented in modern times,
according to NERC.
Nonetheless, the industry has established a special working
group on mitigating the effects. And in May 2013, the Federal
Energy Regulatory Commission formally directed NERC to
develop reliability standards to help protect the US grid
from solar storms ("FERC Order 779: Reliability standards for
geomagnetic disturbances", May 16, 2013).
NERC characterises severe geomagnetic storms as "high impact,
low frequency" (HILF) risks. High impact, low frequency risks
are particularly hard to manage because policymakers must
decide how much money to spend on reducing a risk that would
be catastrophic but seems remote.
However, recent research suggests the probability of a severe
storm hitting Earth may be much higher than NERC assumed.
The worst solar storm on record occurred on September 1,
1859, and was observed by an amateur astronomer in England
called Richard Carrington, after whom the Carrington Event is
A large solar flare erupted from the surface of the Sun
lasting for around five minutes. At the same time, a huge
mass of highly charged particles, known as a coronal mass
ejection (CME), was flung towards Earth at speeds up to 2,000
km per second, according to reconstructions by modern solar
The first particles reached Earth within an hour and the
storm peaked around 17 hours and 40 minutes after the flare
The Carrington Event occurred in a largely pre-electrical
age, so the impact was limited. But it was strong enough to
damage severely the new telegraph systems installed in North
America and Europe.
The next big solar storm, reported in May 1921, brought the
U.S. telegraph service to a halt between the East Coast and
the Mississippi River, blowing fuses and burning some
In March 1989, a severe geomagnetic storm blacked out
Quebec's power grid in less than two minutes - the worst
impact to date.
In October and November 2003, the so-called Halloween storms
caused isolated transformer failures in North America and
Measuring the severity of a storm is tricky because it
depends on so many factors, including the size of the flare,
the scale of coronal mass ejection, the speed at which it
travels from the Sun to Earth, magnetic flux, time of day,
and location of the direct hit.
But one common summary statistic used by solar researchers is
called "disturbance-storm time", or Dst for short.
The Dst index measures how hard Earth's magnetic field shakes
when a storm hits, according to NASA ("Near miss: the solar
superstorm of July 2012").
Dst is measured in nano-Teslas (nT). The more negative Dst
becomes, the worse the storm.
The Carrington Event in 1859 is estimated to have had a Dst
index of around -850 nT. The Quebec storm in 1989 clocked in
at -589 nT and the 1921 storm was probably on a similar
What frightened the solar scientists was that the July 2012
storm would have had a Dst index of up to -1200 nT if it had
struck Earth, making it much worse than the Carrington Event.
Scientists are able to analyse the July 2012 storm in detail
because although it was angled away from Earth it made a
direct hit on a solar observation satellite, STEREO-A, which
is specially hardened to withstand extreme magnetic
But had it hit Earth, it would have done severe damage to
power grids and satellite communications.
Severe solar storms occur much more often than previously
Like many natural phenomena, the frequency with which solar
storms take place scales as an inverse power of the severity
of the event. But the sheer number of large storms over the
last 150 years suggests the Carrington Event is unlikely to
be an isolated occurrence.
Calculations by solar scientist Pete Riley, at Predictive
Science, suggest the probability of a solar storm of at least
the power of the Carrington Event hitting Earth in the next
10 years is around 12 percent ("On the probability of
occurrence of extreme space weather events", February 2012).
While not high, a 12 percent probability hardly qualifies as
a "low-frequency" or remote-probability event.
So it is essential that the power industry and policymakers
better understand how it would impact vulnerable systems
(including the grid, global positioning system, radio and
television communications, satellites and aircraft), harden
them where possible, and plan how to cope with the aftermath
of a big storm.
Once a large flare is detected, the industry and policymakers
would have just an hour or so to put the grid and other
systems into the safest possible operating mode before the
Before the next major storm arrives, it is essential to
understand which transformers and other equipment are most at
Policymakers must consider whether to replace, redesign or
otherwise harden the most at-risk equipment to withstand the
It is also essential to identify how the grid (and other
systems) could be rendered as safe as possible before the
Readying the grid could involve turning the power to
customers down or off to reduce the loading on critical
transformers and make them less vulnerable to overheating.
If power and communications systems are likely to be
disrupted, businesses, households and government agencies
will need to be informed quickly.
And once the storm has passed, grid operators and
policymakers must have a plan for damage repairs.
Grid managers already plan how to re-energise the grid after
large-scale blackouts such as the one that hit the northeast
United States and neighbouring parts of Canada in August
The process is known as a "black start" and involves a
careful sequence of steps to restart power plants,
re-energise power lines and transformers, and gradually
But a severe solar storm might also cause more permanent
damage, so the industry needs to supplement its black start
procedure with a plan for handling multiple transformer
Between 1996 and 2010, the SOHO satellite recorded almost
15,000 coronal mass ejections. It is only a matter of time
before one of them is aimed at Earth and is of the same
magnitude as Carrington, or worse.
Given the frequency of large solar storms, most people
reading this article will witness at least one.
And given society's increasing dependence on electricity and
electromagnetic communications, storms could do much more
damage in future, just one way in which new vulnerabilities
are emerging in high-tech economies.
The biggest threat is probably in emerging markets,
especially middle-income countries, where the combination of
widespread electrification and electronic communications
coupled with outdated and overloaded equipment makes them
But even in the most advanced economies, a severe solar storm
could leave homes and businesses without power for months.
Proper risk management and preparation are therefore
We cannot stop a big solar storm arriving, but we can prepare
and try to avoid its worst effects.
- By John Kemp. The opinions expressed here are those of
the author, a columnist for Reuters