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The
climate of the Earth is always changing. In the past it has altered as
a result of natural causes (think oceans, atmosphere, orbits and
volcanoes). Nowadays the term “climate change” is generally used when
referring to changes in our climate that have occurred over the last
100 years or so. The climate changes we've seen over recent years and
those that are predicted over the remainder of this century are thought
to be mainly as a result of the influence of human behaviour rather
than due to natural changes.
For more than
200 years we have been burning increasing amounts of fossil fuels like
coal, oil and gas, primarily to generate heat, power and light.
However, what we didn’t know until relatively recently was that along
the way we have been creating a bit of a problem. This is because
fossil fuels contain carbon and when we burn them carbon dioxide (CO2)
is released. Too much CO2 is not so good for the climate. So here’s
some commonly used terminology telling why…
The Greenhouse effect
The
“greenhouse effect” is very important when we talk about man-made
climate change. It is a natural effect. A thin layer of gases (what we
term greenhouse gases) in the upper atmosphere act naturally to keep
the Earth at a habitable temperature by trapping some heat (primarily
from the sun) – a bit like a duvet. The thicker the layer, the warmer
the duvet. The six main greenhouse gases, often termed the ‘basket of
6’, are:
• Carbon dioxide (CO2);
• Methane (CH4);
• Nitrous oxide (N2O);
• Hydrofluorocarbons (HFCs);
• Perfluorocarbons (PFCs); and
• Sulphur hexafluoride (SF6)
CO2
is one of the biggest constituents of this layer and scientists have
figured out that the CO2 content thus has a big influence on the
climate.
Global Warming
It
is the extra greenhouse gases (primarily CO2) that we have released
over the last 200 years and continue to release (through power
stations, cars and planes for example) which are now known to pose the
problem. Our activities have bulked up the duvet by approximately one
third of it’s volume and too much heat is now trapped in the system –
thus the term “global warming”.
This warming (due to past
emissions) is already stressing the Earth’s climatic system creating
more extreme weather, melting of the ice caps, floods and droughts.
It’s a bit like leaving a winter weight duvet on the bed in summer –
things are going to get pretty uncomfortable underneath…
Feedback Effects
Added to this there are so-called “feedback effects” in climate change. These can be positive or negative.
An
example of positive feedback is the increased growing rates of some
plants (the “fertilising effect”) caused by higher C02 in the
atmosphere. These plants absorb CO2 and thus to an extent act as a
balance.
An example of negative feedback
is the “Ice Albedo” effect. Ice reflects solar radiation back into the
atmosphere whereas water absorbs solar radiation and gets warmer (like
the Solent in summer – not that we’ve noticed though!). So as the Earth
gets warmer and more ice melts there is less ice to reflect radiation
and a greater expanse of water to absorb radiation. This magnifies the
global warming effect.
Scientists believe
that positive feedbacks have the upper hand and that this is causing
global warming to accelerate exponentially. Think of it as a snowball
rolling down a snow-packed hill picking up ever-increasing amounts of
snow.
Carbon Sinks
The
Earth has a number of natural carbon “sinks” and it is estimated that
these have actually absorbed more than half of C02 emissions over the
last 200 years. This has mainly occurred in oceans but also on land.
Scientists believe, however, that excess levels of CO2 can lead to
these carbon sinks becoming less effective. There are other side
effects too. Higher CO2 leads oceans to become more acidic – enough to
bleach coral the world over.
All the above put simply please!
The
Earth’s natural systems don’t grow in the same way as our activities on
Earth. Thus we are putting stress on these systems. One of the ways
this is manifested is in man-made climate change.
Want to know more about the science and see some nice diagrams?
Here are some useful links:
More on the greenhouse effect and greenhouse gases from BBC Weather:
http://www.bbc.co.uk/climate/evidence/greenhouse_effect_img.shtml
Lots
more on climate change from climate change scientists at Real Climate.
The linked page below allows you to adapt your reading to your existing
level of knowledge so don’t be intimidated by the word scientist!
http://www.realclimate.org/index.php/archives/2007/05/start-here/
And finally myths…
No not urban myths! You can find them elsewhere on the web... We are talking climate change myths and controversies.
Rather then drone on about these we suggest you look at the excellent pages of the Royal Society at:
http://www.royalsoc.ac.uk/page.asp?id=6229
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