• 'Horrible' sea level rise of more than 3 feet plausible by 2100, experts say

    Alister Doyle / Reuters file

    Experts increasingly recognize that ice melting in Antarctica could push up sea levels dramatically higher in coming decades.

    By John Roach, NBC News

    Melting glaciers in Antarctica and Greenland may push up global sea levels more than 3 feet by the end of this century, according to a scientific poll of experts that brings a degree of clarity to a murky and controversial slice of climate science. 

    Such a rise in the seas would displace millions of people from low-lying countries such as Bangladesh, swamp atolls in the Pacific Ocean, cause dikes in Holland to fail, and cost coastal mega-cities from New York to Tokyo billions of dollars for construction of sea walls and other infrastructure to combat the tides.

    "The consequences are horrible," Jonathan Bamber, a glaciologist at the University of Bristol and a co-author of the study published Jan. 6 in the journal Nature Climate Change, told NBC News. 

    Estimating how much sea levels will rise from ice sheet melting is one of the more challenging aspects of climate science. Some evidence suggests recent accelerated melting is related to changes in ocean and atmospheric temperature, though natural variability may play an important role.

    In addition, glaciers respond to external forces such as warmer temperatures in different ways, even when they are located right next to each other. As a result, there is tremendous uncertainty in the scientific community over how the melting will affect sea levels over the next century.

    Bamber and colleague Willy Aspinall attempted to find clarity in the chaos using a scientific polling technique common in fields such as predicting earthquakes and volcanic eruptions, but until now not applied to climate science.

    The pair sent 26 of the world's leading glaciologists a series of questions about the behavior of the Antarctic and Greenland ice sheets. About half replied to the survey in 2010. The respondents were polled again in 2012 to assess the robustness of their answers.

    Bamber said this type of approach is "a lot more than an opinion poll." The experts were handpicked to get a representative perspective of world leaders from the ice sheet modeling and observational fields. "We analyzed the results in a very systematic, rigorous, and statistically robust way," he added.

    The median estimate from the experts is that the melting ice sheets will contribute 1 foot (29 centimeters) to sea level rise by the year 2100 with a 5 percent chance their contribution could exceed 2.8 feet (84 centimeters). When the effect of thermal expansion (water expands as it warms) is taken into account, the high-end estimate is more than 3 feet (1 meter).

    The estimates are higher than the controversial figures in the 2007 report  from the Intergovernmental Panel on Climate Change (IPCC) of up to 23 inches (59 centimeters) and higher than the unpublished estimates being prepared for the next IPCC report, said Bamber, who is a review editor for that document and has seen the estimates.

    The discrepancy likely reflects added weight given to recent studies that indicate glacier melt has accelerated in recent years in Antarctica and Greenland, and that the West Antarctic ice sheet could partially collapse by the end of this century.

    "The numbers we are getting out of our elicitation reflect the fact that the world leaders in this field are now cognizant of the fact that the ice sheets are quite responsive and, in particular, there is a potential for them to make a really quite dramatic contribution," Bamber said.

    The greatest drama would be a more than 3-foot rise in sea levels from the combined effect of melting ice and thermal expansion, which the study indicates has a 1 in 20 chance of occurring. 

    How much of this drama can be attributed to human burning of fossil fuels, the study indicates, remains murky. “There is really no consensus amongst the experts we approached,” Bamber said. “That’s something that we in the scientific community need to address as a matter of urgency.”

    John Roach is a contributing writer for NBC News Digital. To learn more about him, check out his website.

  • Sea level rose 60 percent faster than UN projections, study finds

    A recent study published in the journal "Nature" suggests the U.S. may experience a 5-foot rise in sea level given all of the fossil fuel that has already been burned. NBC's Anne Thompson reports.

    By Miguel Llanos, NBC News

    Projections for sea level rise in coming decades could be too conservative, experts warned Wednesday, saying they found that the rise over the last two decades is much more than predicted by the U.N. scientific body tracking climate signals.


    In a peer-reviewed study, the experts said satellite data show sea levels rose by 3.2 millimeters (0.1 inch) a year from 1993 to 2011 — 60 percent faster than the 2 mm annual rise projected by the U.N.'s Intergovernmental Panel on Climate Change for that period. 

    "This suggests that IPCC sea-level projections for the future may also be biased low," the team wrote in the journal Environmental Research Letters. 

    The experts also said the IPCC was just about spot on with its predictions for warming temperatures.

    "Global warming has not slowed down or is lagging behind the projections," lead author Stefan Rahmstorf, a researcher at Germany's Potsdam Institute for Climate Impact Research, said in a statement. "The IPCC is far from being alarmist and in fact in some cases rather underestimates possible risks." 

    The experts added that the faster sea level rise is unlikely to be caused by a temporary ice discharge from Greenland or Antarctica ice sheets because it correlates very well with the increase in global temperature.

    The IPCC earlier estimated that seas rose by about 7 inches over the last century, and its most recent report, published in 2007, estimated a range of between 7 and 23 inches this century — enough to worsen coastal flooding and erosion during storm surges.

    But the IPCC report did not factor in a possible acceleration of the melt of the Greenland and Antarctic ice sheets.

    The IPCC "assumed that Antarctica will gain enough (ice) mass" to compensate for Greenland ice loss, the new study's authors noted, but more recent studies have shown that "the ice sheets in Greenland and Antarctica are increasingly losing mass."

    Related: Ice melt found across 97 percent of Greenland

    Rahmstorf told Reuters his best estimate for sea level rise was between 20 inches and three feet this century, possibly more if greenhouse gas emissions of carbon dioxide surged.

    In the past century, as the climate has warmed, sea level rise has accelerated. Scientists predict it will only increase, and they're studying changes in the ocean and land to better understand how and why the water is rising. NBC's Anne Thompson reports for "Changing Planet," produced by NBC Learn in partnership with the National Science Foundation.

    The IPCC chair, addressing delegates to international climate talks being held in Doha, Qatar, on Wednesday made note of the recent findings on ice loss and sea level rise.

    The next IPCC report, Rajendra Pachauri promised, will have "a better appreciation of mass loss of the large ice sheets of Greenland and Antarctica."

    When the next IPCC report comes out in March 2014, he added, expect "a more quantitative understanding of ongoing sea level rise" — and an entire chapter on the topic.

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