ICE MELT: Thick ice sheets in Greenland and Antarctica are melting faster than scientists had predicted, contributing more to sea level rise.
Image: Courtesy of NSIDC
Ice loss from the massive ice sheets covering Greenland and Antarctica is accelerating, according to a new study.
If the trend continues, ice sheets could become the dominant contributor to sea level rise sooner than scientists had predicted, concludes the research, which will be published this month in the journal Geophysical Research Letters.
"The traditional view of the loss of land ice on Earth has been that mountain glaciers and ice caps are the dominant contributors, and ice sheets are following behind," said study co-author Eric Rignot, a glaciologist at NASA's Jet Propulsion Laboratory and the University of California, Irvine. "In this study, we are showing that ice sheets, mountain glaciers and ice caps are neck-and-neck."
But that could soon change, Rignot said, because the rate at which ice sheets are losing mass is increasing three times faster than the rate of ice loss from mountain glaciers and ice caps.
"I don't think we expected ice sheets to run neck-and-neck with mountain glaciers, which basically sit in a warmer climate, this soon," he said. "At the same time, the mass loss on the ice sheet is not very large compared to how much mass they store."
Rignot was part of a research team that also included scientists from Utrecht University in the Netherlands and the National Center for Atmospheric Research in Boulder, Colo.
The researchers based their analysis on a comparison of two different methods to measure ice loss.
Sea level rise estimates likely to increase
One source was NASA's twin GRACE satellites, which orbit the Earth about 200 kilometers apart from each other. Small changes in the planet's gravity field can push the satellites together, ever so slightly, or pull them apart -- variations that scientists use to interpret the terrain below.
The second method combined different satellite data that measure the speed at which the ice sheets flow to the ocean, airborne measurements of the ice sheets' thickness and a regional climate model. Combining the speed and thickness measurements allowed the scientists to determine how much ice was flowing into the ocean, while the climate model allowed them to estimate how much snow was falling on the ice sheet. Subtracting one from the other produced a "mass-balance" picture of net ice loss or growth for each ice sheet.
The two data sets overlapped for an eight-year period, from 2002 to 2010, and showed similar results. Based on that close agreement between the two measurement methods, the scientists had confidence that the full 18-year record produced by the mass-balance method was generally accurate.
Rignot said the results are "probably going to provide more incentive for the next [Intergovernmental Panel on Climate Change report] to revise sea level prediction a little bit upwards."
He cautioned that it's hard to extrapolate his new results to the end of the century, because "18 years of data is not too much."
In its last major report, released in 2007, the IPCC predicted seas would rise between 7 and 23 inches by 2100 -- but couched that estimate with a giant caveat. The IPCC cautioned that an additional rise could come from rapid and unpredictable melting in Greenland and Antarctica, which it didn't attempt to estimate.
Since that report was released, scientists have worked hard to improve their understanding of ice sheet behavior and improve estimates of future sea level rise. Many researchers now believe the sea could rise an average of 3 to 6 feet by the end of the century, with the more likely amount at the low end of that range.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
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12 Comments
Add CommentThere are now more than 1.7 billion people living with 50 miles of the seashore. Most are living in urban environments. Rising sea levels may be a problem...
Reply | Report Abuse | Link to thisWe should be grateful for the temperature stabilising impact of melting ice. Think how much warmer it would be if ice had not melted and absorbed the excess energy retained on the surface of the planet. The only thing that increased is the enthalpy (total energy content) of the surface layer of our planet in the process.
Reply | Report Abuse | Link to thisI have always maintained that as long as we have a substantial mass of ice, temperature would not increase. No more ice, then the same amount of energy that melted ice would raise the temperature of the same mass of water from 0C to 80C.
Currently the only impact we are witnessing of population induced surface layer enthalpy increases are more severe storms and perhaps more tectonic and volcanic activity. We also experience more storms as local temperature increases are transferred to cooler regions and ice melts.
Recently we have been reading about satellites that were supposed to monitor heat radiation form our planet ending up as debris. Why do we need satellites? We are retaining more energy as a result of greenhouse gasses, these are heavy opaque gasses and remain in the troposphere (lower layer of the atmosphere), if the stratosphere temperatures have declined, then we know not enough energy is being radiated out to space. An aeroplane travelling in the stratosphere can tell you that.
Latent heat of vaporisation from melting ice does absorb heat. Other reports show that sea ice in Antarctica has increased by a huge amount over the past thirty years & is still increasing. This more than compensates for the melting ice, latent heat theory. Glaciers move at varying speeds & no one knows why. If the ocean levels are going to increase by the amount predicted by the at the bottom of the range they predicted, the level should already have risen by half an inch. Of course the increase would not be linea but in fact it has not increased at all outside the levels of uncertainty when temperature variations are taken into account.
Reply | Report Abuse | Link to thisCarlyle: Floating ice that melts does not increase sea level. Try an experiment yourself, fill a glass half full with ice then fill it with ice cold water to the brim, after the ice has all melted it will not have overflowed except if the temperature rises and the water expands. Don't mistake the condensate water outside the glass as water having overflowed. PS the condensation heats the glass and water.
Reply | Report Abuse | Link to thisNot to be bitchy, but when ice melt the energy it needs to change state from solid to liquid with no change of temperature is the latent heat of fusion or melting (334kJ/kg). Latent heat of vaporisation (water turning to steam at 100C) is a lot more (2260kJ/kg).
Another small point, the ice on the south polar cap is sitting on land, it is very thick and heavy, it applies an enormous pressure on the crust and magma layer beneath it, when it melts this pressure will reduce, either causing the land to rise or allowing magma to rise. Both situation are bad for existing land-based life. Don't worry neither one of us will be around when this happens.
About the reports of ice increases, I am sceptical. It goes against reason. I know the Milankovitch cycle tells me our planet should be cooling as it moves away from the sun.
Satellites have revealed that ice loss and production in Antarctica is highly variable, with some regions experiencing warming and loss of ice while other regions the opposite due to the ozone hole. Since the 1970s satellite images have shown that Antarctic ice has increased about 100,000 square kilometers (62,100 square miles) per decade. The researchers say this increase is not very great, about 0.97 percent per decade.
Reply | Report Abuse | Link to thisThe reason you are sceptical is that it goes against the AGW theory & is not therefore reported widely.
http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=838
Yes latent heat of fusion, but latent heat from solid to liquid is the flip side & not to be confused with from liquid to vapour or steam.
People are being caused to hyperventilate about sea level rises because of glacial melting. This has been going on since the last ice age. We read all about increased rates of melt & glacial retreat but many glaciers are in fact increasing in thickness & volume even as they retreat. Others are in fact simply increasing in both volume & extent. This has always been the case. Again, only the negative excites the media.
Reply | Report Abuse | Link to thisAs for sea ice having an effect on sea levels, to all intents & purposes, it makes no difference unless the melt water increases in temperature & there is resultant expansion but it is minute. What i was refering to is the lack of an increase in sea level from glacial melt in line with the seven year old IPPC prediction, even at their lowest predicted rate.
Carlyle: No I am not worried at all about what is happening, I see it as the sixth extinction running its course. This extinction started when the Homo sapien began to show signs of intelligence and started using agriculture.
Reply | Report Abuse | Link to thisEvolution will proceed and what ever happens, so be it. Perhaps we shall make room for a truly intelligent species. The future is not preordained or anything like that. I had a lot of problems comprehending time, but commentors in this space set my right, and I am grateful. I read Lee Smolin's Three Roads To Quantum Gravity as was suggested, and it did me a world of good.
Science simply is the best thing that ever happened to me. I am just my mind, nothing else matters.
Carlyle- AT this site http://arctic.atmos.uiuc.edu/cryosphere/ , You can do comparisons, for different years and dates, of the extent of the Arctic ice cap in satellite photos. Comparing same dates in 2011 with 2006 will show a major increase in the extent of sea ice. Antarctic ice increase is even more extensive.
Reply | Report Abuse | Link to thisI have seen the data and heard reports from elsewhere in addition to looking at this site that are are quite clear that the Artic ice has receded significantly this fall and winter. One report had the Artic ice receding to an extent second only to 2007 which was the warmest year on record in at least the last 100 years. And 2010 was considered one of the three warmest years ever recorded along with 1998 and 2007.
Reply | Report Abuse | Link to thisIn addition I saw a report that Artic ice had receded to farthest point ever for a January and that was this January 2011. This is actually understandable when we recall this extremely cold winter we have had. And what could that have to do with the record point of ice recession in January? This is the Artic after all. The particularly cold weather this year was due to the Artic Oscillation which was unusually positive this year pushing the cold storm systems further south which resulted in the Artic being unusually warm limiting the ice accumulation. When the Artic Oscillation is negative the cold weather naturally stays north. This positive pressure in Artic Oscillation may in fact be in result of our warming climate but I have not yet seen evidence to such a linkage.
But shouldn't we be looking at the global picture? Why then exclude the evidence that what is lost in one hemisphere is gained in the other? Arctic sea ice loss in some parts is not the full picture either. The cold simply moved south of the arctic circle bringing record cold & snow to those areas. The cold influence has simply temporally shifted geographically. Over all it has not been the result of warming. Simply an oscillation. The areas of additional snow cover together with its reflectivity, are if anything going to lower temperatures. Arctic waters that are not ice covered actually radiate more heat than those covered in ice. The Earth has remarkable feedback mechanism that keep the system in balance.
Reply | Report Abuse | Link to thisYes, I do follow those sites generally though I have not for a while as each year the system seems to go down, sometime for months at a time. A couple of years ago they changed satellites & the data was not compatible with the previous data. It took them many months to reconcile the two systems. Even then, there remained some uncertainty in my mind. If the new system is correct, what about the veracity of the old figures? Makes me wonder how accurate any of it is, especially when comparing with the past. At least these days they are recognising the effect of oscillations in weather patterns & not just blaming global warming. What is not generally recognised is that Arctic ice has been declining since the 1950s this cycle. It has undergone these cycles many times before. There is no doubt that there has been an over riding global warming since the last ice age but in my view it has never been a smooth line & minor bumps are to be expected. If however it is caused by CO2, there should never be a backward step when in fact the rate of temperature increase in recent years has declined while CO2 concentrations have continued to go up.
Reply | Report Abuse | Link to thisOnly Truth and Knowledge can awaken the world & make Nations take note of CLIMATE CHANGE and take corrective steps. There is no time to waste. Earth and its environment is unstable so too is humanity. Materialistic Rich and religious people who know not God are leading the world to disaster. Someone give serious thought to Principle and Design on which Nature functions to sustain the temperature of earth. How she works to sustain the energy to matter ratio http://www.scribd.com/doc/114273537/Climate-Change-and-Its-Relation-to-Energy
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