Rise in sea level can't be stopped: scientists

LONDON Sun Jul 1, 2012 1:02pm EDT

Icebergs are reflected in the calm waters at the mouth of the Jakobshavn ice fjord near Ilulissat in Greenland in this photo taken May 15, 2007. REUTERS/Bob Strong/Files

Icebergs are reflected in the calm waters at the mouth of the Jakobshavn ice fjord near Ilulissat in Greenland in this photo taken May 15, 2007.

Credit: Reuters/Bob Strong/Files

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LONDON (Reuters) - Rising sea levels cannot be stopped over the next several hundred years, even if deep emissions cuts lower global average temperatures, but they can be slowed down, climate scientists said in a study on Sunday.

A lot of climate research shows that rising greenhouse gas emissions are responsible for increasing global average surface temperatures by about 0.17 degrees Celsius a decade from 1980-2010 and for a sea level rise of about 2.3mm a year from 2005-2010 as ice caps and glaciers melt.

Rising sea levels threaten about a tenth of the world's population who live in low-lying areas and islands which are at risk of flooding, including the Caribbean, Maldives and Asia-Pacific island groups.

More than 180 countries are negotiating a new global climate pact which will come into force by 2020 and force all nations to cut emissions to limit warming to below 2 degrees Celsius this century - a level scientists say is the minimum required to avert catastrophic effects.

But even if the most ambitious emissions cuts are made, it might not be enough to stop sea levels rising due to the thermal expansion of sea water, said scientists at the United States' National Centre for Atmospheric Research, U.S. research organization Climate Central and Centre for Australian Weather and Climate Research in Melbourne.

"Even with aggressive mitigation measures that limit global warming to less than 2 degrees above pre-industrial values by 2100, and with decreases of global temperature in the 22nd and 23rd centuries ... sea level continues to rise after 2100," they said in the journal Nature Climate Change.

This is because as warmer temperatures penetrate deep into the sea, the water warms and expands as the heat mixes through different ocean regions.

Even if global average temperatures fall and the surface layer of the sea cools, heat would still be mixed down into the deeper layers of the ocean, causing continued rises in sea levels.

If global average temperatures continue to rise, the melting of ice sheets and glaciers would only add to the problem.

The scientists calculated that if the deepest emissions cuts were made and global temperatures cooled to 0.83 degrees in 2100 - forecast based on the 1986-2005 average - and 0.55 degrees by 2300, the sea level rise due to thermal expansion would continue to increase - from 14.2cm in 2100 to 24.2cm in 2300.

If the weakest emissions cuts were made, temperatures could rise to 3.91 degrees Celsius in 2100 and the sea level rise could increase to 32.3cm, increasing to 139.4cm by 2300.

"Though sea-level rise cannot be stopped for at least the next several hundred years, with aggressive mitigation it can be slowed down, and this would buy time for adaptation measures to be adopted," the scientists added.

The study is available at www.nature.com/nclimate (Reporting by Nina Chestney; Editing by Pravin Char)

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Comments (9)
AuAgExpl wrote:
Something to think about: the global climate has been warming since the end of the last Ice Age ~10000 years ago and although humans have contributed to an acceleration of this process, the rise in sea level was going to happen regardless. The alternative (global cooling) would be far more onerous to us as humans.

The global climate is not static and understanding that fact is useful in any realistic discussion about “Global Climate Change”.

Jul 01, 2012 5:24pm EDT  --  Report as abuse
T0M wrote:
The climate changes all the time, regardless of whether humans are here or not. The difference is that past climate changes have taken many millennia, allowing the ecosystem to adapt through evolution, whereas humans are changing the climate so fast that essential species cannot evolve at the required rate. A thousand years might seem a lot to modern human society but to a species of grass, or insect, or fish it is just the blink of an eye. Fish can’t deal with greater oceanic acidity by wearing protective equipment, they have to evolve to adapt to it.

Jul 01, 2012 6:51pm EDT  --  Report as abuse
AuAgExpl wrote:
TOM: Don’t disagree with the basics of your reply to my comment. However the climate can and often does change rapidly at times, i.e. several “mini ice ages” over the last few thousand years. These events had nothing to do with human interaction with the environment. If you look over longer time periods (during the Eocene, Miocene and further back into the Cretaceous and Jurassic), there is significant evidence of rapid climate change. I do agree that we as humans are influencing the environment, but there are other factors that should be considered in a discussion about climate. There is an obvious lack of balance about this politically charged issue.

Jul 02, 2012 10:58am EDT  --  Report as abuse
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