Climate change will shake the Earth
By Bill McGuire
The idea that a changing climate can persuade the ground to
shake, volcanoes to rumble and tsunamis to crash on to unsuspecting coastlines
seems, at first, to be bordering on the insane. How can what happens in the
thin envelope of gas that shrouds and protects our world possibly influence the
potentially Earth-shattering processes that operate deep beneath the surface?
The fact that it does reflects a failure of our imagination and a limited
understanding of the manner in which the different physical components of our
planet – the atmosphere, the oceans, and the solid Earth, or geosphere –
intertwine and interact.
If we think about climate change at all, most of us do so in
a very simplistic way: so, the weather might get a bit warmer; floods and
droughts may become more of a problem and sea levels will slowly creep upwards.
Evidence reveals, however, that our planet is an almost unimaginably
complicated beast, which reacts to a dramatically changing climate in all
manner of different ways; a few – like the aforementioned – straightforward and
predictable; some surprising and others downright implausible. Into the latter
category fall the manifold responses of the geosphere.
The world we inhabit has an outer rind that is
extraordinarily sensitive to change. While the Earth's crust may seem safe and
secure, the geological calamities that happen with alarming regularity confirm
that this is not the case.
Here in the UK, we only have to go back a couple years to April 2010, when the word on everyone's lips was Eyjafjallajökull – the ice-covered Icelandic volcano that brought UK and European air traffic to a grinding halt. Less than a year ago, our planet's ability to shock and awe headed the news once again as the east coast of Japan was bludgeoned by a cataclysmic combination of megaquake and tsunami, resulting – at a quarter of a trillion dollars or so – in the biggest natural-catastrophe bill ever.
Here in the UK, we only have to go back a couple years to April 2010, when the word on everyone's lips was Eyjafjallajökull – the ice-covered Icelandic volcano that brought UK and European air traffic to a grinding halt. Less than a year ago, our planet's ability to shock and awe headed the news once again as the east coast of Japan was bludgeoned by a cataclysmic combination of megaquake and tsunami, resulting – at a quarter of a trillion dollars or so – in the biggest natural-catastrophe bill ever.
In the light of such events, it somehow seems appropriate to
imagine the Earth beneath our feet as a slumbering giant that tosses and turns
periodically in response to various pokes and prods. Mostly, these are supplied
by the stresses and strains associated with the eternal dance of a dozen or so
rocky tectonic plates across the face of our world; a sedate waltz that
proceeds at about the speed that fingernails grow. Changes in the environment
too, however, have a key role to play in waking the giant, as growing numbers
of geological studies targeting our post-ice age world have disclosed.
Between about 20,000 and 5,000 years ago, our planet
underwent an astonishing climatic transformation. Over the course of this
period, it flipped from the frigid wasteland of deepest and darkest ice age to
the – broadly speaking – balmy, temperate world upon which our civilisation has
developed and thrived. During this extraordinarily dynamic episode, as the
immense ice sheets melted and colossal volumes of water were decanted back into
the oceans, the pressures acting on the solid Earth also underwent massive
change. In response, the crust bounced and bent, rocking our planet with a
resurgence in volcanic activity, a proliferation of seismic shocks and
burgeoning giant landslides.
The most spectacular geological effects were reserved for
high latitudes. Here, the crust across much of northern Europe and North
America had been forced down by hundreds of metres and held at bay for tens of
thousands of years beneath the weight of sheets of ice 20 times thicker than
the height of the London Eye. As the ice dissipated in soaring temperatures,
the crust popped back up like a coiled spring released, at the same time
tearing open major faults and triggering great earthquakes in places where they
are unheard of today. Even now, the crust underpinning those parts of Europe
and North America formerly imprisoned beneath the great continental ice sheets
continues to rise – albeit at a far more sedate rate.
As last year's events in Japan most ably demonstrated, when
the ground shakes violently beneath the sea, a tsunami may not be far behind.
These unstoppable walls of water are hardly a surprise when they happen within
the so-called ring of fire that encompasses the Pacific basin but in the more
tectonically benign North Atlantic their manifestation could reasonably be
regarded as a bit of a shock. Nonetheless, there is plenty of good, hard
evidence that this was the case during post-glacial times. Trapped within the
thick layers of peat that pass for soil on Shetland – the UK's northernmost
outpost – are intrusions of sand that testify to the inland penetration of
three tsunamis during the last 10,000 years.
Volcanic blasts too can be added to the portfolio of
postglacial geological pandemonium; the warming climate being greeted by an
unprecedented fiery outburst that wracked Iceland as its frozen carapace
dwindled, and against which the recent ashy ejaculation from the island's most
unpronounceable volcano pales.
The huge environmental changes that accompanied the rapid
post-glacial warming of our world were not confined to the top and bottom of
the planet. All that meltwater had to go somewhere, and as the ice sheets
dwindled, so the oceans grew. An astounding 52m cubic kilometres of water was
sucked from the oceans to form the ice sheets, causing sea levels to plummet by
about 130 metres – the height of the Wembley stadium arch. As the ice sheets
melted so this gigantic volume of water was returned, bending the crust around
the margins of the ocean basins under the enormous added weight, and provoking
volcanoes in the vicinity to erupt and faults to rupture, bringing geological
mayhem to regions remote from the ice's polar fastnesses.
The breathtaking response of the geosphere as the great ice
sheets crumbled might be considered as providing little more than an intriguing
insight into the prehistoric workings of our world, were it not for the fact
that our planet is once again in the throes an extraordinary climatic
transformation – this time brought about by human activities. Clearly, the
Earth of the early 21st century bears little resemblance to the frozen world of
20,000 years ago. Today, there are no great continental ice sheets to dispose
of, while the ocean basins are already pretty much topped up. On the other
hand, climate change projections repeatedly support the thesis that global
average temperatures could rise at least as rapidly in the course of the next
century or so as during post-glacial times, reaching levels at high latitudes
capable of driving catastrophic breakup of polar ice sheets as thick as those
that once covered much of Europe and North America. Could it be then, that if
we continue to allow greenhouse gas emissions to rise unchecked and fuel
serious warming, our planet's crust will begin to toss and turn once again?
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