CLIMATE
CHANGE IN WALES -
A GEOLOGIST'S PERSPECTIVE
PART 2: UNDERSTANDING THE PRESENT
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FACTORS
WITHIN AND BEYOND OUR CONTROL
The palaeoclimatic fluctuations described in part
1 were due to factors beyond our control.
Increased or decreased solar output, subtle
variations in Earth's orbit, changing patterns of
oceanic currents and products of volcanic
activity have all played their part. To this
equation we must now add the changes to the
composition of Earth's atmosphere as a direct
consequence of human industrial activity, on top
of which all other factors will continue to play
their part as they always have done.
So let's have a look at some present-day issues
which, partly affected by our activities and
partly natural, have a bearing on how our climate
may change in the medium term.
SOLAR RADIATION AND THE ALBEDO EFFECT
Our planet is warmed by intense radiation from
the sun. Without it, Earth would not be
habitable. The radiation passes through the
atmosphere (after certain wavelengths being
filtered out by the ozone layer) and is absorbed
or reflected by the surface. The ability of a
surface to reflect sunlight (also known as
albedo) is controlled by its composition. Snow
and ice are much better reflectors than rock or
water, for instance:
Above: a heavy snowfall over
Cadair Idris, February 2004. The snow's bright
white appearance hints at the amount of solar
radiation that simply reflects off it. The albedo
value for fresh snow can be as high as 90%...
Above: Plynlimon shimmers in
a summer heatwave in July 2003. Land such as this
reflects much less incoming solar radiation and
absorbs most of it. The albedo value for
moorlands such as these is well below 20%.
An easy way to demonstrate the effects of
differing albedo values is to go out on a hot
summer's day in a black T-shirt. You'll cook!
White clothing is far more comfortable in
heatwaves because it has a higher albedo value
and reflects more incoming radiation than it
absorbs.
Thus, in our current situation, we rely on the
polar and mountain icecaps to assist in
reflecting a proportion of the Sun's radiation
back out into space. The less snow and ice there
is, the less this reflectance can occur: instead
more energy is absorbed. The more energy that's
absorbed the warmer it gets and the more likely
further melting is to occur. So that's one
factor.
GREENHOUSE GASES - THE INFRA-RED TRAP
Greenhouse gases absorb heat energy which is
trying to escape by radiation out into space. If
you leave your car locked up on a sunny day then
open it up after a few hours you'll have
witnessed the greenhouse effect for yourself:
while the car is very good at absorbing the
incoming solar radiation, it's hopeless at
getting rid of the consequent infra-red (heat)
radiation that it generates, so that increasingly
warmer air remains trapped inside until you open
it and allow the airflow to bring the temperature
back to an acceptable level.
To a certain extent we need greenhouse gases. It
is estimated that they maintain the current
avarage global temperature (about 15oC)
some 33oC
above what it would otherwise be. In other words,
without them we would have an average global
temperature of -18oC.
So to an extent greenhouse gases are beneficial.
To an extent. Look at Venus, where CO2
forms over 95% of the atmosphere and the surface
temperature is in excess of 460oC.
That's an excellent example of the greenhouse
effect taken to an extreme - the planetary
equivalent of that car parked all afternoon in
blazing sunshine. So we need that happy medium -
not too much, not too little. Let's have a closer
look:
Above: an extremely
simplistic representation of the heat-exchanges
going on within Earth's atmosphere. Visible solar
radiation (yellow) is partly absorbed and partly
reflected by clouds and the Earth's surface. When
such radiation is absorbed, the excitation of
molecules in the absorbent (rocks, water,
buildings etc) causes them to emit heat
(infra-red) radiation (orange). Some of this
escapes out to space via various complex routes.
Greenhouse gases are able to absorb, rather than
transmit, infra-red photons, and cause a
"back-radiation" back towards the lower
layers of the atmosphere. This in turn raises the
temperature of those lower layers.
There are several greenhouse gases present in the
atmosphere, of which carbon dioxide is the one in
the news most of the time. It is established fact
that levels of atmospheric CO2
have increased during the
last 100 years, from about 290 parts per million
(ppm) in 1900 to around 375ppm now. The
Intergovernmental Panel on Climate Change has
extrapolated the rate of increase forward to
2100: the results indicate that, if unchecked,
atmospheric CO2 will
by then be somewhere between 650 to 970ppm. This
in turn has been projected to cause an average
global temperature increase of 1.4 to 5.8oC.
Significant - or is it?
Advocates of a blissful continuity in the way we
are doing things often cite palaeoclimatic
figures at this point. There is evidence, for
example, that CO2
levels 500 million years ago were approximately
20 times greater than at the present day, and by
200 million years ago were still at 5 times the
modern level. Therefore what's the problem? Our
atmosphere is deficient in CO2!
All well and good, but remember, we are living in
an unusual phase of Earth history in which we
have experienced repeated, and in geological
terms sudden, climatic oscillations from glacial
to interglacial. These have been happening over
quite predictable cycles, in the recent past.
What we don't entirely know is how human
interference with atmospheric composition effects
these cycles. Yet there are some direct effects
that we can consider:
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SEA-LEVEL
RISE DUE TO BULK-MELTING OF GLACIAL ICE
The retreat of glaciers is well-documented from
many areas of the world. Both direct melting and
changes in precipitation (trends towards dryer
conditions create a deficit in snowfall,
inhibiting new ice formation) play their part.
The result is that ablation of glacial ice by
melting and sublimation is currently exceeding
the rate of new ice generation with two results:
firstly, glaciers are indeed retreating and
secondly, and more importantly in the short-term,
sea-levels are rising gradually.
Above: a sketch-map of NW
Europe about 10,000 years ago. Much more land is
present than there is now because so much water
was still trapped within the retreating ice. In
Wales, all of Cardigan Bay was land: in fact, it
has been estimated that the sea in this area rose
by 90m as the last ice-age came to an end.
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Above: by 7,500 years ago
the more familiar shape was emerging....
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Above: ...while 6000 years
ago it was pretty much as today.
The rate of sea-level rise following the end of
the last glaciation has slowed as the phenomenon
of isostatic adjustment has caught up with the
rising waters. Isostatic adjustment in this
context is the uplift of land that has formerly
been under the pressure of a heavy ice-cap for
thousands of years. It is a slow process that
continues today and is responsible for some of
the earthquakes that the UK experiences as
movements take place along geological faults to
adjust to the stresses set up by uplift. More
pronounced in the northern UK (because this is
where the greatest ice thicknesses were), its
effects are less important further south: in
fact, instead of rising, far southern areas are
very gradually sinking
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Although
the rate of sea-level rise is currently slow, the
rate of melting of glacial ice is according to
many climatologists on the increase. The
projected 2100 CO2 and
temperature levels are a cause for concern as
they will only encourage further melting: should
the trend continue, the results could be serious.
Why?
Because,
for the first time EVER in geological history, we
have a warming climate plus continued melting
plus large centres of human civilisation
established in low-lying coastal areas. It didn't
matter to us whether or not the polar ice-caps
were present during the Cretaceous Period. We
weren't around to get worried. This time it's
different.
Above: high tide at Borth,
on the Cardigan Bay coast, during the infamous
Burns' Day Storm of 1990. It is not hard to
imagine what would have happened, had the
high-tide level been just a metre higher. Coastal
population centres are especially vulnerable to
sea-level rises.
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COOLING
AND DROUGHT: LESSONS FROM THE EARLY HOLOCENE
Another issue that merits concern is the
triggering of a cooling episode which may lead to
prolonged dry and windy conditions. Ideal for
desert generation, very unfortunate with a large
population to feed.
Cooling
episodes that lead to such conditions, such as
the Younger Dryas and the early Holocene events
are thought to have been triggered by large
releases of cool, fresh water, derived by
ice-melt, entering the sea in northern latitudes.
Such occurrences can affect the thermohaline
circulation of an ocean. Our currently mild,
temperate climate is influenced by one such
circulation - the North Atlantic Drift. Warm,
salty water of relatively low density flows at
the surface northwards, is cooled in wintertime
and sinks in Arctic regions to the ocean floor.
This deeper, cooled water then makes its way back
south. Simplistically it's like a large
conveyor-belt: trouble can occur if someone drops
a wrench into one of the pulleys driving it.
Large ejections of meltwater can do just this.
Above: highly simplified
diagram of a functional North Atlantic. The
supply of the near-surface warm water drives our
climate in NW Europe, which is far milder than it
would otherwise be for the latitude.
If the thermohaline circulation is interrupted,
the warm water cannot make it so far northwards
and colder conditions extend further to the
south. The lack of warm water interferes with the
humidity of the troposphere (the bottom ~10km of
the atmosphere where most of our weather goes on)
- the lack of moisture means dryer weather
patterns.
A prolonged disruption of the thermohaline
circulation coupled with natural factors such as
reduced solar input could see a progressively
colder climate becoming established. The data
from ice-cores suggest that this happens steadily
(as opposed to "The Day After
Tomorrow"), but inexorably. In the previous
Holocene cooling events, renewed warming occurred
and the climate recovered. The worst possible
scenario is a steady deterioration into another
full-blown glacial episode. Never mind that: it
would take many centuries. Shorter-term cooling
events like that which occurred 6000 years BP are
potentially serious in the extreme. Why?
Because, for the first time EVER in geological
history, we have a huge global population
entirely dependant on successful global
agriculture and the ability to distribute its
products from the areas where production occurs
to the areas where most of the products are
consumed. Most of us in the West rely totally on
this system to be successful. If it even
half-fails due to a change to cool, dry
conditions, we are in deep trouble. We don't even
need a full-blown new Ice-age to create chaos.
CAUSE FOR CONCERN, OR ENVIRONMENTAL
SCAREMONGERING?
So: will this happen? What will we see - further
warming and deglaciation, accompanied by rising
sea-levels, or a cooling event causing drought or
even triggering a glacial advance? The truth is
that, currently, we do not know - as ever we need
more data - but given that there is now a large
population in the way of any advancing climatic
adversity, we need to do our best to find out and
adjust the way in which our societies are
organised accordingly.
We are organised in such a way that we are
incredibly vulnerable to even localised severe
weather events. A good example is thus: for
centuries, we avoided building houses on the
flood-plains of major rivers. But in recent years
society has begun to regard the natural world as
something that gets in the way of
"progress" and the climate and its
effects have been ignored. Housing estates have
thus been appearing on flood-plains all over the
place. And guess what? They have ended up being
flooded. That's what happens on flood-plains, for
heavens' sake! If the prevailing mindset is the
one that ignores such irritations because they
interfere with "progress" then we are
already in deep trouble! And that's just one
example.
It is surely better to understand any potential
problems caused by our activities and attempt to
deal with them, rather than to ignore the whole
issue and possibly get a nasty surprise. For all
the wealth and confidence of Western society, we
are still entirely controlled by the natural
world about us. We have to accept this absolute.
Currently it supports us and our pleasantly
indulgent lifestyles. One day it may be less
capable of doing so, for all of our inventiveness
and sophistication.
Put it another way. Here's a question. You have
driven up a mountain pass, only to find at the
top that your car's brakes do not appear to be
working properly. The pedal feels a bit soft, and
there's something that looks suspiciously like
brake fluid dripping onto the tarmac underneath.
Do you:
a) Phone a breakdown service
on your mobile and get it trailered off to a
garage mechanic in order to check them out and,
if necessary, fix them. Better safe than sorry.
Or:
b) Pretend that there's
nothing wrong, jump back into the drivers seat,
and drive at high speed down the other side of
the pass, where you know there are lots of
hairpin bends and nasty drops?
Most of us don't know enough about braking
systems to be confident enough to continue, and
those who knew what was wrong wouldn't continue
full stop. What will it take for us to develop a
greater awareness of our changeable, sometimes
friendly, but sometimes hostile, climate?
Remember again:
Climate change (impact
definition): Change of the climate system that is
faster than the adaptation time of social and/or
ecosystems.
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