Scientists say the data is clear that sea levels have risen significantly | Pacific Beat

Scientists say the data is clear that sea levels have risen significantly

Scientists say the data is clear that sea levels have risen significantly

Updated 1 April 2013, 17:04 AEDT

For many islands nations and vast stretches of coastal communities in the Pacific, sea level rises are a reality that clouds their future.

Heading the list of countries most endangered by global warning are Tuvalu, Kiribati and Marshall Islands.

Scientists are very clear about their predictions of significant sea levels rises in the future.

But what hard data do we have already to prove the trend.

Cathy Harper reports, leading agencies in the region, including Australia's Bureau of Meteorology, the C-S-I-R-O and the University of Hawaii all say the data is clear that sea levels are rising.

Presenter: Cathy Harper

Speakers: Phil Thompson, Sea Level Centre, University of Hawaii; John Church, CSIRO fellow, Centre for Australian Weather and Climate Research; David Jones, manager of climate monitoring and prediction, Australian Bureau of Meteorology

HARPER: The Sea Level Center at the University of Hawaii does research on regional sea levels.

An expert at the Center, Phil Thompson, says there's lots of good quality data available on sea levels.

THOMPSON: The Sea Level Center here in Hawaii we operate tide gauges, but that's only one of the measurements that we use to study sea level There are also satellite altimeters which are satellites that fly around the world and they measure height within about a few centimetres over most of the ocean. Which give us a really complete picture of how sea levels are changing almost everywhere on Earth. The primary limitation of the satellite data though is that those actually weren't actually launched until the early 1990s so the question becomes what we're observing with the satellites now, how does that fit into the longer term context like during the twentieth century and that's where we use the tide gauges.

HARPER: What does the data that we have tell us about what sea levels in the tropical Pacific actually doing?

THOMPSON: Well, sea levels in the Western Tropical Pacific have actually been going up very fast in recent decades and we know this very well from what I was talking about with the satellite measurements of sea level. So global sea level over the past two decades or so rose about six centimetres, about. However in the western tropical Pacific with Guam and those areas in the Philippines sea levels actually increased about 30 centimetres during that same two decades which is roughly five times as much as the global rate. In contrast to that however, sea levels in the eastern Pacific have actually changed very little over the same time period. So it's actually an important question as to why sea levels would be changing, rising so rapidly in the West and not really rising in the east. And the simple answer to that is because of the wind. The trade winds that blow from east to west over the tropical Pacific have actually been increasing in strength over the past couple of decades. And that's led to sea levels rising faster in the west and slower in the east. And actually if we look at tide gauges of sea levels in those areas in earlier decades, such as the 50s, 60s and 70s that situation was actually reversed and sea levels were rising faster in the east and slower in the west.

HARPER: These fluctuations have also been observed by John Church - a CSIRO fellow at the Centre for Australian Weather and Climate Research, which is a partnership between the CSIRO and Australia's Bureau of Meteorology.

CHURCH: We believe these are natural phenomena so they've happened before, and they're superimposed on the climate change signal. Now there is a question which you could ask ... Is some of this pattern actually related to a pattern of climate change such that climate change is resulting in an increased strength of the south east trades and the trade winds in the equatorial Pacific and I think the answer to that is really not known.

HARPER: There's no doubt in John Church's mind, however, that sea levels globally, and in the Pacific, have been rising steadily over the past century.

The Australian Bureau of Meteorology - another leading Australian agency in terms of sea levels - says the data on what sea levels have done in the past is clear.

Dr David Jones is the manager of climate monitoring and prediction at the Bureau.

JONES: Things like sea level are remarkably easy to cross check to compare against other variables, such as temperature, to compare against what's happening with the ice sheets. And scientists are doing this all the time. I guess there's a couple of safeguards here for science. One is that people look for consistency. So you don't just pick out one tide gauge and say, well is this the global trend. We look at hundreds or thousands of data and draw a general conclusion. The other one is really that we're always looking at our own results and ways of looking at other people's results. So there is continuous cross checking. If things don't look right your peers will usually tell you and tell you in no uncertain terms. So you know, look, the results are very robust and absolutely no alternative conclusion other than that sea levels are rising.

HARPER: There are a lot of warnings around for countries in the Pacific especially to prepare for rising sea levels. Is that necessary if we're really not sure exactly what sea levels are going to do in the future? For example, if the rises in the western Pacific that we've seen over the past few decades then reverse in the next few decades?

JONES: Well, we will see variability, so every single year, the sea level won't be higher. But in the long term the trends are fairly obvious. We're expecting something around about 50 centimetres of further sea level rise this century. Now we might get lucky and it might be more like 20 or 30 centimetres. Or we might get unlucky and it may end up around a metre. But the story is very clear. You know, people have to prepare for a rise in sea level, higher sea levels on average in the future, more erosion, more coastal inundation, so there really is a clear need for people to prepare and adapt.

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