CSIRO's Dr John
Church is one of the world's leading sea level rise experts. Dr
Church is coordinating lead author of the Sea Level Change chapter
of the IPCC Fifth Assessment Report.
Harden Up brings you four specially produced videos that were
developed to help Queenslanders learn about sea level rise, and we
are delighted to offer Dr Chruch's perspectives.
The interview transcript below helps to explain what is
happening as our oceans warm and why.
CSIRO transcript
Title: Sea level on the rise
Duration: 5m:28s
Location: http://www.csiro.au/multimedia/pfq8.html
or listen here: http://www.csiro.au/files/files/pcc8.mp3
Transcript:
Narrator:
You're listening to CSIROpod, from
the CSIRO, Australia's leading scientific research
organisation.
Ms Kylie Johnson:
Hello, and welcome to CSIROpod, I'm
Kylie Johnson.
An international team of scientists has found the climate system
may be responding more quickly to rising carbon emissions than
previously estimated. The scientists' findings are being
published in the journal Science. The scientists include John
Church from the CSIRO's Climate, Marine and Atmospheric Research
Division, as well as researchers from Toulouse in France, the
Potsdam Institute of Climate Research in Germany, the NASA Goddard
Institute for Space Studies, and the Scripps Institution of
Oceanography in the United States, and the Hadley Centre in the
United Kingdom.
The scientists studied actual observations of carbon dioxide,
temperature and sea level rises from 1990 until 2006, comparing
them with forecasts made by climate models. While
temperatures were in the upper range of predictions, sea levels are
rising faster than originally thought. John Church explains
why the sea levels are climbing.
Dr John Church:
The most important reason for sea
level rise in the 20th century, and we expect to be in the 21st
century, is oceans thermal expansion. As the ocean warms the
water expands, sea level rises.
The second largest contribution is
from the melting of glaciers and ice caps, so these are glaciers in
places like Alaska, the Himalayas, New Zealand, Switzerland, etc.,
and they've been melting, and melting an increasing rate over the
past 50 years.
And the third contribution, and potentially the largest
contribution on the longer timeframe, but we don't think there's
been a large contribution in the last century, are the ice sheets
of Greenland and Antarctica. Greenland contains enough water
to raise sea levels by about seven metres, and Antarctica over 60
metres.
We know surface melting is increasing in Greenland and that's
flowing into the ocean and contributing to sea level rise, and in
Antarctica it is primarily too cold for surface melting with the
exception of the Antarctic Peninsula.
However, there are a number of uncertainties about the ice sheet
contributions to sea level. For example in Greenland some of the
surface melt we believe is actually flowing down to the base of the
Greenland ice sheet, and that could be potentially lubricating the
base of the ice sheet and potentially allowing the glaciers to
slide more rapidly into the ocean, contributing further to sea
level.
So this is a process which we don't adequately model at the
current time. In Antarctica one of the concerns is warm ocean
water penetrating under the west Antarctic ice sheet, and the west
Antarctic ice sheet is grounded below sea level, so this water can
penetrate underneath the ice sheet melting the ice sheet from below
and allowing a more rapid dynamic response.
Ms Kylie Johnson:
Imagine that if there is criticism
of this research it would be that it's over a very limited time
period. How confident are you in the observation data?
Dr John Church:
The observations of temperature have
been compiled by two different sources - by the GIST Center in the
US and the Hadley Centre in the UK. The sea level data comes
from two sources also. Satellite altimeter data are used from
the period 1993 to the present, and that gives essentially a global
coverage.
Tide gauge data is used over a much
longer period so we've actually estimated global average sea levels
from 1870 to the present using the tide gauge data and information
from the satellite altimeter data to help us interpolate between
the tide gauges.
Ms Kylie Johnson:
And what was CSIRO's role in the
research?
Dr John Church:
Our biggest contribution over the
recent years has been to estimate global average sea level over the
period from 1870 up to the present using a combination of tide
gauge and satellite altimeter data.
We're now trying to estimate the
amount of thermal expansion of the ocean and increase in ocean heat
content over the period from 1950 up until the present. This
is a difficult and challenging issue, but we feel we're making
progress and we feel we will have a better estimate than the
previous estimates.
Once we have this estimate we will
then attempt to more critically test the latest set of IPCC models
and the projections.
Ms Kylie Johnson:
Dr John Church, thanks for your time
today.
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