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Mike's Australia


23 Climate change
I am not going to get involved in the reasons for climate change. That has
become a highly politicised subject and is best avoided when you want to talk
about outcomes. Suffice it to say that climate is changing all the time and
sometimes with profound consequences for landforms and lifestyles.
The Great Barrier Reef owes its existence to climate change. The story of how this
happened was being researched when I took a job at James Cook University in
Townsville as its press officer. That was back in the 1980s and the university was one
of the few scientific research establishments in northern Australia.
The university's geologists and marine scientists combined in a joint project to drill
into the reef and take core samples. They proceeded in much the same way as
archaeologists do when they dig to uncover the past. The project was condemned by
green activists who claimed (quite erroneously) that the researchers were drilling for
oil.
The scientists ignored the protests and went ahead with the full approval of the
Great Barrier Reef Marine Park Authority, which is responsible for the preservation of
the Reef.
We now know that the Reef, in its present form, dates from the end of the last Ice
Age, 18,000 years ago. At that time, vast amounts of water were locked away as ice in
Antarctica and elsewhere. Sea levels were 120 metres (400 ft) lower than at present.
When the ice melted, the sea rose and made its way inland.
In those not-so-far-off days, a string of low hills dotted the coast of what is now
northern Queensland. They were the eroded remnants of an earlier barrier reef and
were covered in vegetation. The rising water reached the hills and made islands of
them.
Coral animals were washed in from the continental shelf and formed fringing reefs
about the islands. The reefs grew upwards as the water continued to rise. Since coral
needs light to grow and prosper, the growth was fastest in the shallows. Corals in low-
lying areas got left behind and died. The result was a string of sharply defined reefs
along the line of the former barrier reef. In a sense, the old reef system was reborn.
About 6000 years ago, the melting largely ceased and the sea reached something
like its present level. This had a variety of consequences and one was the
development of reef flats. Corals cannot live out of water for more than a few hours.
The sea is flat and that sets a limit to growth in the upward direction.
If you dive on the Barrier Reef, you will come upon extensive areas of reef flat. The
corals that grow there are robust ... built to withstand crashing waves. If you venture to
the edge of the flats you will often encounter a cliff-like drop-off. The corals that live on
the drop-off tend to protrude outwards to catch the light. Further down, in calmer
waters, more delicate corals grow.
In geological terms, the Barrier Reef is very young. It is old by human standards but
not so old as one might think. Aboriginal people were living in Australia when the Ice
Age came to an end 18,000 years ago.
 
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