Ecocentric

Climate Change: Polar Ice Sheets Melting Faster, Raising Sea Levels

The rate of polar ice-sheet melting is key to calculating how fast sea levels are rising. Now, scientists have a new analysis of polar ice loss in Greenland and Antarctica—and the numbers aren't good for the planet.

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Image courtesy of Ian Joughin

Surface water rushes along a crack in the Greenland ice sheet. Melting from the polar ice sheets has accelerated sea level rise

Superstorm Sandy, which made landfall on the East Coast a month ago yesterday, wasn’t a particularly powerful storm. But what it did have was water—lots of it. Sandy pushed record storm surges in places like lower Manhattan, and it was the flooding triggered by those surges—much more than the winds accompanying the storm—that caused the tens of billions of dollars in damages attributed to the Superstorm.

But our coastlines were already primed for those kinds of catastrophic floods, thanks in part to the gradual rise in sea level over the past century caused chiefly by man-made global warming. Sea levels have risen by about half a foot over the past century—and are likely rising even faster along the U.S. Northeastern coast—which amplified the effects of Sandy’s storm surges. That’s why scientists are so worried about the impacts that climate change to come may have on sea levels. The higher the seas rise, the more devastating coastal storms will become.

Unfortunately, trying to predict how rapidly the seas will rise as the climate warms is extremely difficult. We know that as ocean temperatures increase—which goes hand in hand with global warming—water expands and sea levels rise. But the big X factor is the polar ice sheets chiefly found in Greenland and Antarctica. As that massive land ice melts, the water flows directly into the seas, causing the water to rise. By contrast, sea ice melting—which has been occurring at a record pace in the Arctic this summer—does not raise the sea levels, just as the melting of an ice cube in a glass of scotch doesn’t raise the overall level of liquid.

The problem is that scientists have struggled to nail down just how quickly the polar ice sheets are melting. There have been more than 30 different estimates of sea level contributing due to polar ice sheet melting made since 1989. But in a new paper published in the November 29 Science, a team of researchers have gone through all of those estimates and come to a broadly agreed conclusion that melting from the ice sheets have contributed an average of 0.023 in (0.59 mm) to sea-level rise since 1992, with an uncertainty of 0.008 in. (0.2 mm) per year. That might not sound like much—ice-sheet melting has only added about half an inch (12.7 mm) to sea levels in that time span—but the new analysis means that polar ice sheets are melting three times faster today than they did in the 1990s, with much of the ice loss happening in Greenland. “This will give the wider climate science community greater confidence in ice losses and lead to improved mode predictions of future sea-level rise,” said Andrew Shepherd, a professor of earth observation at the University of Leeds and a co-author of the Science paper.

(PHOTOS: Portraits of Melting Glaciers)

Most of that melting appears to be happening to the Greenland ice sheet, which holds nearly 700,000 cu. miles of ice, although the even more massive Antarctic ice sheet is melting as well—though not as uniformly as in the Arctic. (In Antarctica—which has an ice sheet the size of the U.S. and Mexico combined—parts of the continent are melting, while other parts seem to be growing.) In the 1990s, the two ice sheets combined on average to lose 110 billion tons of ice a year. That sounds like a lot—actually, that is a lot—but keep in mind that it takes about 10 trillion tons of ice melting to raise sea levels by an inch. But that rate increased to 379 billion tons a year between 2005 and 2010—and the Science paper doesn’t include information from 2012, when the Greenland ice sheet experienced a record thaw.

(MORE: Unfrozen Tundra)

The study may not seem earth-shattering, but it does what earth science needs to do: give us a clearer picture of what’s happening to our planet. The mechanics of polar ice-sheet melting were so confusing that the 2007 Intergovernmental Panel on Climate Change assessment simply didn’t include ice loss estimates in its attempt to model future sea level rise. Said co-author Benjamin Smith, a research scientist at the University of Washington:

It provides a simpler picture. In the 1990s, not very much was happening. Sometime around 1999, the ice sheets started losing more mass, and probably have been losing mass more rapidly over time since then.

Of course, what the data doesn’t tell us is what we should actually be doing about ice-sheet melting, sea-level rise and climate change. (Although if the sleep-walking delegates at the U.N. climate summit in Doha this week and next week are any measure, the answer is “not much.”) But we shouldn’t kid ourselves that there won’t be major costs if we fail to slow the pace of warming—and that we’ll eventually have to pay the bill. Sandy helped teach us that.

MORE: Arctic Sea Ice Larger Than U.S. Melted This Year

29 comments
solid2gas
solid2gas

Water expands as it gets cold not warm. Great science reporting Mr. Wizard.

MarkGoldes
MarkGoldes

Another Time Bomb is a surprisingly possible solar superstorm.

See the Aesop Institute website for some comments on how preventing thatfrom causing a nuclear nightmare can accelerate the superseding offossil fuels. 

Cheap Green and Moving Beyond Oil on that website provide a few detailsregarding revolutionary technologies that may make that happen much morerapidly than might be readily imagined.

BlueRock
BlueRock

In a way, I'm glad to see that there aren't any well-informed, rational people posting comments here anymore. It's just kooks and 8th-graders. Why is that encouraging? Because the high-information people have dropped out of the the so-called "debate". The debate among the experts was over 10 or 20 years ago. People who have been reading about this issue for years know that we're in big trouble. Now it's only a question of how much destruction is coming and how soon.

BenditBecket
BenditBecket

Excellent.  I'm tired of shoveling snow. 

OzarkGranny
OzarkGranny

Because I worry about this, I bought a push mower (as in one without a motor).  What are others doing to make a difference?

GregoryLawrenceFaith
GregoryLawrenceFaith

Wow......I'm amazed at what I am reading here. Earth is a living planet and through time it has changed many times over. All you have to do is to look around to see that. There is obviously no real intelligent life on it. I can read that in any newspaper or online source as proof.

Dachman
Dachman

Wow the sea levels have risen 1/2" since 1992, that must have made a huge difference in the hurricane in NY & NJ.

That 1/2" added hundreds of dollars in damages, maybe even thousands...

We have not had a level 4 or 5 all year and a level 2 hits the most populated portion of the US at high tide and everyone screams global warming, what a joke!

Pat
Pat

Come on people, melting ice doesn't change the level of the ocean, even if it was true, don't believe me, put ice in your cup, fill it with water, it will never overflow, this is STUPID science at it's best.... ridiculous.

JimSatterfield
JimSatterfield

And the trolls come out to play. jalangaya apparently understands nothing of what creates arable land or else he wouldn't think there is some under ice that has been in place for thousands of years and whose progress across the land during its creation has a tendency to strip topsoil from rock. DavidNutzuki has an unreadable rant after making a strange comment that would seem to indicate he doesn't believe that CO2 is a greenhouse gas. Is this the best the denier community can produce?

jalangaya
jalangaya

This is good news for humanity. With that ice out of the way, we can see what was hidden. Maybe oil. Maybe gold. Or, arable land for farming & homesteads.

DavidNutzuki
DavidNutzuki

Only the fear mongering news editors still spew this CO2 madness:

*Occupywallstreet does not even mention CO2 in its list of demands because of the bank-funded carbon trading stock markets run by corporations.*Obama has not mentioned the crisis in the last two State of the Unions addresses.*In all of the debates Obama hadn’t planned to mention climate change once.*Julian Assange is of course a climate change denier.*Canada killed Y2Kyoto with a freely elected climate change denying prime minister and nobody cared, especially the millions of scientists warning us of unstoppable warming (a comet hit).And still after 26 years the IPCC has NEVER said it WILL happen, only will happen; “maybe” or “could be” or “likely”….and yet they say we could be at the point of no return, maybe…… Exaggeration isn’t a crime, yet.

kirkaiya
kirkaiya

@solid2gas Actually, while water expands as it experiences a phase transition from liquid to solid (ice), and just prior to that point as well, water also expands as it warmsSo, "Mr. Wizard" was absolutely correct - and much of the measured rise in sea-levels is due to thermal expansion rather than an increase in the number of water molecules.

BlueRock
BlueRock

Did you even read the article?

hubert.arnold1
hubert.arnold1

@GregoryLawrenceFaith  Gregory, you have said it all and in a very short space. I have always thought that the animals on our planet were more intelligent than many humans.

OzarkGranny
OzarkGranny

@GregoryLawrenceFaith I live about a dozen miles from the ocean. I'm always telling my grand kids "Don't sell the house.  One day it will be beachfront property."

BlueRock
BlueRock

Thank you for your unscientific, unhelpful, 8th grade-level comments.

kirkaiya
kirkaiya

@Pat Pat, did you not read the article at all?  The author makes that very point about arctic sea-ice, but notes that the ice in question is on top of Greenland (the Greenland ice-sheet), which is fresh-water, and not floating, so as it melts, it absolutely does raise the level of the ocean.  If the entire Greenland ice-sheet were to melt, the average increase in sea-level would be roughly 16 feet, but higher in some parts of the world (the level of the ocean is not exactly the same everywhere nor at all times, due to ocean currents, the tides, and the fact that the Earth is not a perfect sphere).

KaelaWhite
KaelaWhite

@Pat yes your right it doesn't overflow this is because the ice is in the water from the start. when you add ice to your cup when its at the brim then it will over flow. this is what they are talking about not sea ice but land ice the ice/water that is not even in the water. and we are not talking about a little extra water we are talking about Antarctica, Arctic, and Greenland ice sheets coming into the ocean....suddenly it doesn't seem so stupid

JimSatterfield
JimSatterfield

@SamFelton It is not part of the discussion because one of the things about Milankovitch cycles is that astronomers can pretty much tell where we are in one and how much it should be influencing temperature in the absence of other influences. Those who have asked them know that the answer is that they do not account for current temperatures or the rate of change of those temperatures.

Pat
Pat

@JimSatterfield If you find yourself without facts and concepts to discuss and refute man-caused global warming or “climate change” as nonsense read the following:Water vapor is a better absorber of heat energy, IR, than CO2 by a factor of seven and has 30 to 100 times as many molecules in air that generate 210 to 700 times as much atmospheric heat as CO2. Water vapor does 99.96% to 99.99% of all atmospheric heating. Why should we stop using our best, most convenient, abundant, lowest cost form of energy to quell 0.01% to 0.04% of atmospheric heating? The Medieval Warming period was the happiest in history. 500 years of peace and prosperity. Why is this nonsense happening?The control and taxing of carbon and carbon dioxide would give the elected ruling class more money and power than anything in history. For them and the 40% of our people wanting more government so they get “benefits" by “taxing the rich” and "spreading the wealth around," could make it happen!Man makes so little CO2 compared to nature cutting our portion would net nothing even if it were a good absorber of IR. Earth produces 166 billion tons (gigatons) of CO2 every year. 160 gigatons come from the decomposition of limestone and dead stuff. Of the six gigatons made by man America makes 20% or 1.2 gigatons, but with it we make 50% of the world’s fuel, fiber, food and manufactured goods. The Green-a-zoids want us to cut our production of CO2 by 80% or by 0.96 gigatons, but of the 166 gigaton total that is only 0.57%, a statistically insignificant portion of the total of which 96% is produced naturally and CO2 is the vapor tiger.

yoshason
yoshason

@jalangaya Even if that land was arable it would not be added land, but at best replacement land for all the costal land lost due to rising sea levels.

glubber
glubber

@BlueRock Sorry to you two, the snow and ice is already here in nothern Norway!.

wmceachron
wmceachron

 @Pat @JimSatterfield -  Your numbers are accurate, but I disagree with your conclusions.  Natural earth systems produce about 770 gigatons of CO2 per year, and they are capable of sequestering about 785  gigatons of CO2 per year.  Burning fossil fuel and land use ( cutting down forest to make farmland, etc) produces about 29 gigatons of CO2.  That is more then the sequestration system can absorb, and this causes the extra CO2 to sit in the atmosphere.  Currently the CO2 levels are at higher then they have been in the last 15 million years.  As for the water vapor - it is absolutely true the water vapor effects the temp more then CO2.  But the water vapor cycle is basically a "closed" system.  The amount of water vapor in the air is dependent on temperature.  The higher the temp, the more turbulent the water vapor cycle becomes (more evaporation and precipitation).  So the more CO2 you add to the atmosphere, the more water vapor you get in the atmosphere.  

Dachman
Dachman

So you are saying if all of Greenland was melted clear of ice that an equal ammount of land would be covered due to the rise in sea level? That is why so many people don't listen to the Global Warming hype.

I would not doubt that one of the Time writer quotes you as an expert.

nellre
nellre

West Antartic is collapsing.