I
suspect that I am not the only one who has wondered about the
connection between the recent hurricanes in the Caribbean and the two
earthquakes in Mexico that coincided with them.
"The bottom line is that as climate change tightens its grip, we must be prepared to expect the unexpected"
How
climate change triggers earthquakes, tsunamis and volcanoes
Global
warming may not only be causing more destructive hurricanes, it could
also be shaking the ground beneath our feet
Bill
McGuire
16
October, 2016
Devastating
hurricane? More than 1,000 lives lost? It must be climate change!
Almost inevitably, Hurricane Matthew’s recent rampage across the
Caribbean and south-eastern US has been fingered by some as a
backlash of global warming driven by humanity’s polluting
activities, but does this really stack up?
The
short answer is no. Blame for a single storm cannot be laid at
climate change’s door, as reinforced by the bigger picture. The
current hurricane season is by no means extraordinary, and the last
few seasons have actually been very tame. The 2013 season saw no
major hurricanes at all and tied with 1982 for the fewest hurricanes
since 1930. This, in turn, is no big deal as there is great
year-on-year variability in the level of hurricane activity, which
responds to various natural factors such as El Niño and the
so-called Atlantic Multidecadal Oscillation, as well as the
progressive warming of the oceans as climate change bites harder.
The
current consensus holds that while a warmer world will not
necessarily mean more hurricanes, it will see a rise in the frequency
of the most powerful, and therefore more destructive, variety. This
view was supported recently by Kerry Emanuel, a hurricane scientist
at MIT, who pointed to Matthew as a likely sign of things to come.
Debate
within the hurricane science community has in recent decades been
almost as hostile as the storms themselves, with researchers, on
occasion, even refusing to sit on the same panels at conferences. At
the heart of this sometimes acrimonious dispute has been the validity
of the Atlantic hurricane record and the robustness of the idea that
hurricane activity had been broadly ratcheting up since the 1980s.
Now, the weight of evidence looks to have come down on the side of a
broad and significant increase in hurricane activity that is
primarily driven by progressive warming of the climate. For many, the
bottom line is the sea surface temperature, which is a major driver
of hurricane activity and storm intensification. Last year saw the
warmest sea temperatures on record, so it should not be a surprise.
As Michael Mann, an atmospheric scientist at Penn State University,
says: “It isn’t a coincidence that we’ve seen the strongest
hurricane in both hemispheres [western and eastern] within the last
year.” As the Atlantic continues to heat up, the trend is widely
expected to be towards more powerful and wetter storms, so that
Matthew might seem like pretty small beer when looked back on from
the mid-century.
As
with hurricanes, Pacific typhoons and the mid-latitude storms that
periodically batter the UK and Europe are forecast to follow a
similar pattern in an anthropogenically warmed world. Storm numbers
may not rise, but there is likely to be an escalation in the
frequency of the bigger storm systems, which tend to be the most
destructive. An additional concern is that mid-latitude storms may
become clustered, bringing the prospect of extended periods of
damaging and disruptive winds. The jury is out on whether climate
change will drive up the number of smaller, but potentially ruinous
vortices of solid wind that make up tornadoes, although an apparent
trend in the US towards more powerful storms has been blamed by some
on a warming atmosphere.
Tornadoes,
typhoons, hurricanes and mid-latitude storms – along with heatwaves
and floods – are widely regarded as climate change’s shock
troops; forecast to accelerate the destruction, loss of life and
financial pain as planet Earth continues to heat up. It would be
wrong to imagine, however, that climate change and the extreme events
it drives are all about higher temperatures and a bit more wind and
rain.
An
earthquake fault that is ready to go is like a coiled spring – all
that is needed is the pressure of a handshake
The
atmosphere is far from isolated and interacts with other elements of
the so-called “Earth system”, such as the oceans, ice caps and
even the ground beneath our feet, in complex and often unexpected
ways capable of making our world more dangerous. We are pretty
familiar with the idea that the oceans swell as a consequence of the
plunging atmospheric pressure at the heart of powerful storms,
building surges driven onshore by high winds that can be massively
destructive. Similarly, it does not stretch the imagination to
appreciate that a warmer atmosphere promotes greater melting of the
polar ice caps, thereby raising sea levels and increasing the risk of
coastal flooding. But, more extraordinarily, the thin layer of gases
that hosts the weather and fosters global warming really does
interact with the solid Earth – the so-called geosphere — in such
a way as to make climate change an even bigger threat.
This
relationship is marvellously illustrated by a piece of research
published in the journal Nature in 2009 by Chi-Ching Liu of the
Institute of Earth Sciences at Taipei’s Academia Sinica. In the
paper, Liu and his colleagues provided convincing evidence for a link
between typhoons barrelling across Taiwan and the timing of small
earthquakes beneath the island. Their take on the connection is that
the reduced atmospheric pressure that characterises these powerful
Pacific equivalents of hurricanes is sufficient to allow earthquake
faults deep within the crust to move more easily and release
accumulated strain. This may sound far fetched, but an earthquake
fault that is primed and ready to go is like a coiled spring, and as
geophysicist John McCloskey of the University of Ulster is fond of
pointing out, all that is needed to set it off is – quite literally
– “the pressure of a handshake”.
Perhaps
even more astonishingly, Liu and his team proposed that storms might
act as safety valves, repeatedly short-circuiting the buildup of
dangerous levels of strain that otherwise could eventually instigate
large, destructive earthquakes. This might explain, the researchers
say, why the contact between the Eurasian and Philippine Sea tectonic
plates, in the vicinity of Taiwan, has far less in the way of major
quakes than further north where the plate boundary swings past Japan.
In
a similar vein, it seems that the huge volume of rain dumped by
tropical cyclones, leading to severe flooding, may also be linked to
earthquakes. The University of Miami’s Shimon Wdowinski has noticed
that in some parts of the tropics – Taiwan included – large
earthquakes have a tendency to follow exceptionally wet hurricanes or
typhoons, most notably the devastating quake that took up to 220,000
lives in Haiti in 2010. It is possible that floodwaters are
lubricating fault planes, but Wdowinski has another explanation. He
thinks that the erosion of landslides caused by the torrential rains
acts to reduce the weight on any fault below, allowing it to move
more easily.
It
has been known for some time that rainfall also influences the
pattern of earthquake activity in the Himalayas, where the 2015 Nepal
earthquake took close to 9,000 lives, and where the threat of future
devastating quakes is very high. During the summer monsoon season,
prodigious quantities of rain soak into the lowlands of the
Indo-Gangetic plain, immediately to the south of the mountain range,
which then slowly drains away over the next few months. This annual
rainwater loading and unloading of the crust is mirrored by the level
of earthquake activity, which is significantly lower during the
summer months than during the winter.
Nepal
earthquake: drone footage shows devastation in ancient town of
Bhaktapur
And
it isn’t only earthquake faults that today’s storms and
torrential rains are capable of shaking up. Volcanoes seem to be
susceptible too. On the Caribbean island of Montserrat, heavy rains
have been implicated in triggering eruptions of the active lava dome
that dominates the Soufrière Hills volcano. Stranger still, Alaska’s
Pavlof volcano appears to respond not to wind or rain, but to tiny
seasonal changes in sea level. The volcano seems to prefer to erupt
in the late autumn and winter, when weather patterns are such that
water levels adjacent to this coastal volcano climb by a few tens of
centimetres. This is enough to bend the crust beneath the volcano,
allowing magma to be squeezed out, according to geophysicist Steve
McNutt of the University of South Florida, “like toothpaste out of
a tube”.
If
today’s weather can bring forth earthquakes and magma from the
Earth’s crust, it doesn’t take much to imagine how the solid
Earth is likely to respond to the large-scale environmental
adjustments that accompany rapid climate change. In fact, we don’t
have to imagine at all. The last time our world experienced serious
warming was at the end of the last ice age when, between about 20,000
and 10,000 years ago, temperatures rose by six degrees centigrade,
melting the great continental ice sheets and pushing up sea levels by
more than 120m.
The
bottom line is that as climate change tightens its grip, we must be
prepared to expect the unexpected
These
huge changes triggered geological mayhem. As the kilometres-thick
Scandinavian ice sheet vanished, the faults beneath released the
accumulated strain of tens of millennia, spawning massive magnitude
eight earthquakes. Quakes of this scale are taken for granted today
around the Pacific Ocean’s “Ring of Fire”, but they are
completely out of place in Santa’s Lapland. Across the Norwegian
Sea, in Iceland, the volcanoes long buried beneath a kilometre of ice
were also rejuvenated as the suffocating ice load melted away,
prompting a “volcano storm” about 12,000 years ago that saw the
level of activity increase by up to 50 times.
Now,
global average temperatures are shooting up again and are already
more than one degree centigrade higher than during preindustrial
times. It should come as no surprise that the solid Earth is starting
to respond once more. In southern Alaska, which has in places lost a
vertical kilometre of ice cover, the reduced load on the crust is
already increasing the level of seismic activity. In high mountain
ranges across the world from the Caucasus in the north to New
Zealand’s southern Alps, longer and more intense heatwaves are
melting the ice and thawing the permafrost that keeps mountain faces
intact, leading to a rise in major landslides.
Does
this all mean that we are in for a more geologically active future as
well as a hotter and meteorologically more violent one? Well, no one
is suggesting that we will see a great surge in the number of
earthquakes and volcanic eruptions. As always, these will be
controlled largely by local geological conditions. Where an
earthquake fault or volcano is primed and ready to go, however,
climate change may provide that extra helping hand that brings
forward the timing of a quake or eruption that would eventually have
happened anyway.
As
the world continues to heat up, any geological response is likely to
be most obvious where climate change is driving the biggest
environmental changes – for example, in areas where ice and
permafrost are vanishing fast, or in coastal regions where rising sea
levels will play an increasing role. Freysteinn Sigmundsson of the
Nordic Volcanological Centre observes that the centre of Iceland is
now rising by more than three centimetres a year in response to
shrinking glaciers. Studies undertaken by Sigmundsson and his
colleagues forecast that the reduced pressures that result will lead
to the formation of significant volumes of new magma deep under
Iceland. Whether this will translate into more or bigger eruptions
remains uncertain, but the aviation chaos that arose from the
Eyjafjallajökull eruption in 2010 provides a salutary warning of the
disruption that any future increase in Icelandic volcanic activity
may cause across the North Atlantic region.
A
cloud of ash rises from the volcano under the Eyjafjallajökull
glacier in Iceland in May, 2010, causing chaos for millions of
airline passengers as flights were cancelled across Europe.
Photograph: Ingolfur Juliusson/Reuters
Volcanologist
Hugh Tuffen, of Lancaster University, is worried about the stability
of the more than 10% of active volcanoes that are ice-covered. He
says that “climate change is driving rapid melting of ice on many
volcanoes worldwide, triggering unloading as ice is removed. As well
as encouraging magma to rise to the surface, leading to increased
volcanic activity, removal of ice can also destabilise steep volcano
flanks, making hazardous landslides more likely.”
The
potential for more landslides is also likely to be a problem in high
mountain ranges as the ice cover that stabilises rock faces vanishes.
Christian Huggel of the University of Zurich has warned that “in
densely populated and developed regions such as the European Alps,
serious consequences have to be considered from [future] large slope
failures”.
Looking
ahead, one of the key places to watch will be Greenland, where recent
findings by a research team led by Shfaqat Khan of Denmark’s
Technical University reveal a staggering loss of 272bn tonnes of ice
a year over the last decade. GPS measurements show that, like
Scandinavia at the end of the last ice age, Greenland and the whole
of the surrounding region is already rising in response to the
removal of this ice load. Andrea Hampel of the University of
Hannover’s Geological Institute, who with colleagues has been
studying this behaviour, is concerned that “future ice loss may
trigger earthquakes of intermediate to large magnitude if the crust
underneath the modern ice cap contains faults prone to failure”.
More
earthquakes in Greenland might not seem like a big deal, but this
could have far wider ramifications. About 8,200 years ago, an
earthquake linked to the uplift of Scandinavia, triggered the
Storegga Slide; a gigantic undersea sediment slide that sent a
tsunami racing across the North Atlantic. Run-up heights were more
than 20m in the Shetlands and six metres along the east coast of
Scotland, and the event has been blamed for the flooding of
Doggerland; the inhabited Mesolithic landmass that occupied what is
now the southern North Sea.
The
submerged margins of Greenland are currently not very well mapped, so
the likelihood of a future earthquake triggering a landslide capable
of generating a major tsunami in the North Atlantic is unknown. Dave
Tappin, a tsunami expert at the British Geological Survey, points out
that one large, undersea landslide has been identified off the coast
of Greenland, but suspects that there may not be sufficient sediment
to generate landslides as large as Storegga. Nonetheless, the seismic
revival of Greenland is certainly a geological response to climate
change that we need to keep an eye on.
The
bottom line in all of this is that as climate change tightens its
grip, we should certainly contemplate more and bigger Hurricane
Matthews. However, when it comes to the manifold hazardous by-blows
of an overheating planet, and especially those involving the ground
we stand on, we must also be prepared to expect the unexpected.
Bill
McGuire is professor emeritus in geophysical and climate hazards at
UCL. His current book is Waking the Giant: How a Changing Climate
Triggers Earthquakes, Tsunamis and Volcanoes.
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