New research suggests greater sea level rise
Climate change is expected to cause a greater rise to global sea levels than previously thought. That's according to scientific research presented at recent conferences and lectures around the Gulf of Mexico.
In 2007 the U.N. Intergovernmental Panel on Climate Change predicted a ½- to 2- foot rise in sea level by the end of the century. But recent trends in global sea level, temperature and glacial melting suggest these estimates are on the low end of the spectrum.
Steven Nerem is Associate Director of the Colorado Center for Astrodynamics Research at the University of Colorado and spoke at the Eminent Scholar Lecture Series at USF St. Petersburg yesterday.
“They suggested the range by 2100 was going to be about from 20 cm to about 60 cm possible sea level rise. But there was a very important caveat here. Model based ranges excluding future rapid dynamical changes in ice flow. Well I hope I convinced you today that we have already seen rapid dynamical changes in ice flow. So these numbers down here we can probably dispense with and look at other scenarios. So some would say that the 4th assessment for sea level was conservative because of this. I predict in the next IPCC assessment you are going to see this range move up towards the meter level. I think 1 meter is in play, it is a possibility by 2100.”
Global temperatures is rising at the high end of predictions, which could accelerate the pace of sea level rise, said Nathaniel Plant, oceanographer at the U.S. Geological Survey in St. Petersburg who just returned from an International Conference on Sea Level Rise held in Texas.
“The other is to look at the measured changes in sea level, so what is actually happening and we are tracking at the high end. And there is one more and this is the big one, if you look at the global temperature prediction and that is relatively well measured, the global temperature is actually increasing at the highest end of what the IPCC considered. The forcing of all this melting is at the upper end therefore the implied response will be that the sea level rise will be at the upper end."
The recent rate of global sea level rise is between 2.5 and 3.5 millimeters per year, based on satellite measurements. Nerem said the rise is due to a combination of factors; melting of ice on land, subsidence of land and at least half from water warming up and expanding or thermal expansion.
“When we introduce a heat source and we heat up the water, well just like the mercury in your thermometer, water when heated up expands and causes sea levels to go up. And that is one of the responses to a changing climate. About 80 percent of the heat from climate change is going into the ocean and that is causing thermal expansion of the water and causing a suitable rise.”
In the future, however, if glaciers on land, ice caps and the ice sheets of Greenland and Antarctica give way to greater melting, they have the possibility of raising sea levels even more: up to a meter or more. These formations are already showing signs of doing so.
“Since the 1960s we have seen the glaciers contributing about a ½ mm per year to sea level rise but that has been increasing over the satellite era, it has been going up about 1 mm per year and if you look at more recent data it suggests that it is even more than a 1 mm per year.”
Like future warming, sea level rise will not occur uniformly. Some areas will see greater rise while others not as much.
Sea level in St. Petersburg rose about an inch per decade over the last half century, according to tide gauge records, and is likely to accelerate in the coming decades. Plant says if trends continue - or worse, accelerate - it would create greater vulnerability to the coast and population centers.
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“A raise in sea level is going to flood more and more of that land. The second part is that we have storms and beaches are eroding and every time you raise the average sea level up a little bit you expose more and more of the coast to the impact of the storms. So potentially the erosion rates can increase due to the sea level rise. Throw on top of that perhaps the storminess isn’t going to be the same and the latest scenario suggests that we are going to have more very large storms and fewer hurricanes overall so they all play some part together.”