Sea level riseSea level rise

Sea level rise

 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.

john church pic

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:  or listen here:



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.

sea level rise variability

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.