How much ice is swelling the sea?
There isn’t a doubt in the world (among serious scientists, anyway) that the sea has been rising for the past century, by about eight inches in total since 1900. There’s little doubt, either, that the rise has been speeding up over the past couple of decades – the water has been inching up about as twice as fast lately as it was for most of the 20th century.
All of that is a powerful confirmation of what thermometers tell us: that the earth is warming – the result, say those same serious scientists, of human-generated, heat-trapping greenhouse gases. That heat makes seawater expand, and it also transforms land-based ice into even more water that swells the oceans further.
What nobody has firmly pinned down so far, though, is just how big a contribution all that new water makes to the rising seas. They’ve come up with an estimate, by calculating how much should come from heat expansion then blaming the rest on melting ice: about 1.8 millimeters per year, says University of Colorado physicist John Wahr. But that’s not as convincing as a direct measurement, and it doesn’t solve the mystery of where all the ice is disappearing from.
The mountain ice in the Himalayas (pictured above), Karakorams and other high ranges to the south of the Tibetan plateau, a region so icy it’s sometimes called the “third pole", has lost only about 1 per cent of the worldwide total. Credit: TopTenList.org
Now, however, thanks to Wahr and three other scientists, the measurement question and the mystery have both been answered. Using a high-flying pair of satellites known collectively as GRACE, the Gravity Recovery and Climate Experiment mission, they’ve been watching carefully since 2002 to see, among other things, which of the planet’s glaciers and ice sheets are shrinking and by how much. The answer, just reported in Nature: between 2003 and 2010, about 385 billion tons of ice have vanished into the sea each year – enough, says Wahr, “to fill Lake Erie with water eight times over, or cover the entire US with water to a depth of a foot and a half.”
As it turns out, that comes pretty close to what the estimators were saying before GRACE weighed in. That’s a good thing, since it means ice and sea-level experts were on the right track. They were also right that the greatest contribution by far is coming from the huge masses of ice sitting atop Greenland and Antarctica.
But there was one big surprise: the mountain ice in the Himalayas, Karakorams and other high ranges to the south of the Tibetan plateau – a region so icy it’s sometimes called the “third pole" – has lost only a paltry 4 billion tons of ice annually over the study period, or about 1 per cent of the worldwide total. It was, said Wahr, “a big surprise” that it was so little, and that the bulk of the loss outside Antarctica and Greenland is coming from other mountain ranges. But then, previous estimates of ice loss in that region have been based on very limited measurements on the ground, and weren’t trusted all that much in the first place.
Aside from that, the new, more reliable numbers on ice loss won’t give much comfort to those who have something to fear from the rising sea, which means hundreds of millions of people living in coastal cities around the world, from New York to Shanghai to Amsterdam to Calcutta. For the people who live on the Indian subcontinent and Southeast Asia, though, the news may be a little rosier: the great rivers that water the region have their source in those same high mountains. If the ice that feeds those rivers is mostly staying intact, there’s less chance that the rivers will start to run dry.
Average changes in ice thickness in centimeters per year from 2003 to 2010, as measured by NASA’s Grace satellites, in each of the world’s ice caps and glacier systems outside of Greenland and Antarctica. Blue represents ice mass loss, while red represents ice mass gain. Credit: NASA/JPL-Caltech/University of Colorado
But while the new research finally nails down what’s been happening during the past decade or so, Wahr warns that it doesn’t necessarily tell us what will happen in the future. “In 2004,” he says, “glaciers in southeast Greenland suddenly started moving faster toward the sea. Then they stopped, and glaciers in the north and west started to speed up.” The GRACE measurements will help scientists monitor future changes more accurately, but for now they’re just the beginning of the biggest wild card in figuring out how high, and how fast, the sea will rise.
This article was originally published on Climate Central – www.climatecentral.org. Reproduced with permission.
Comments on this article
denialist response
Timothy,
An honest response from you. You deny that sea level is rising and even it if is (which it patently is) you don't believe there is anything that can be done about it.
I urge readers to stay with the facts and not beliefs. Sea level is rising and the melting of the ice caps indicates that this is accelerating. So there is a problem, especially when the industrialised world has chosen to build its infrastructure within a metre or so of sea level.
Massive change faces us. However, in this case of sea level rise we are responsible. We are making it happen. The problem is that our leaders are in denial, most probably because it is a hard problem and it means we have to change the srtucture of our energy system.
The exciting part is that there are solutions and they are not a gleam in the eye. They are ready and being implemented elsewhere.
It is sad that we in Australia, with the best solar and wind resources in the world and the most to lose from climate change, are struggling at the back of the pack.
Maverick science alright
Keith,
If you want hard evidence of higher sea levels then just look at the east coast of Australia, good examples are Manly, Woy Woy and Cairns - whereby you can see the level of the old tidal flats. The ocean was there before and will be again - as for humans building in these spots well they will just have to adapt, suck as much CO2 out of the atmosphere as you like but you are not going to change this fact.
Sea level rise; the only reliable measurement of Global Warming
Firstly confirmed measurement of sea level rise is difficult. Land based measurements suffer elevation and subsidence. Tides have an 18.5 year cycle and multiple cycles are required to remove the effects of storms, and current changes. That being said the data shows a minimum sea level rise of about 1mm/year for up to the last 200 years. Because the volume of sea level rise comes almost exclusively from continental ice melt, thermal expansion is small, the heat of Global Warming is proportional to the increase in volume of sea water. But sea level is rising a minimum of 1mm/year radially hence the heat of Global warming is increasing at a cubed rate with the volume of sea level rise.
When the heat value of Global Warming is calculated it is the same order of magnitude as the heat released each year by burning fossil fuels.
Dan
maverick science
Timothy
Your link is to an ABC report on a maverick scientist in 2000. Why does this report trump all of the careful science that says for the past 8000 years sea levels have been pretty stable?
Notwithstanding the above cherry picking, we are causing the warming and hence the melt. It is our blowtorch (burning fossil fuels) that is making the accelerated rise happen.
Have a look at what effect a 2 metre sea level rise will have on the financial capitals of the world, and then tell me we should just encourage the warming to happen.
As I've said before this isn't a joke.
Sea Levels
Keith,
Sea levels were up to 2 metres higher than today only 4,000 years ago according to an Australian research team http://www.abc.net.au/quantum/stories/s112352.htm
but I guess all that backburning that the aboriginies did resulted in AGW !
The total mass measured with
The total mass measured with gravity data will include all mass including snow, ice, rocks and water. No need for any further subtractions or additions.
Article is about glaciers, not sea-ice Peter. Sea - ice will melt at a rate proportional to the water temperature. Increased sea-ice melt may be a concern as indicator of increased water-temperature. Often sea-ice is holding back landed ice or glaciers, less sea-ice, faster glaciers will flow into ocean, faster/higher sea-level rise.
ice loss in arctic and antarctic
Peter,
Data (not opinion) shows dramatic thinning of sea ice both in the arctic (see link in my post) and the antarctic. This means acceleration towards allowing ice on land to get into the ocean (being measured, so not opinion)... this will lead to consequent sea level rise, just as extra heat absorbed by ocean (and not reflected by ice) will mean more warming... in the arctic already much more warming than in temperate latitudes.
The sea level rises caused by the above are going to be in addition to the 3.1mm/yr seen currently. There will be estimates soon as to what this is going to mean, but not a good time to relax and just hope it will go away.
Sea Level
Assuming 3.1mm, per year as pointed out by Bernard Walsh, in 50 years we still have only 155mm (6.10 inches), hardly enough to make you desert your seaside property, in the event you live that long.
lost at the start...
There isn’t a doubt in the world (among serious scientists, anyway)
lost me right here with bias and innuendo ..i.e. if you differ you are not serious. What a great way to shut down discussion....anyway..I persisted..and read on.
The claim is that water is flowing equivalent to a foot deep..etc..because of glacier melt, but forgot to subtract increased snowfall in Antarctica (blamed for WA's drought) and the increase in sea ice formation.
Another slanted and incomplete piece of pseudo-science from scientists who want to be noticed and then stop looking when their biases are met.
....and by the way for all those stressing about icebergs melting and Arctic sea ice melt etc..it makes very little difference to water levels as most of the berg is below the current sea level. I assume the brilliant authors of this research have already included the retreating glaciers in Antarctica, so its all a bit of a beat up....especially about melting icebergs. The ice under the water when melting does not increase the level...just relax a bit and less hyperventillation.
big changes at the poles
In the arctic, the rate of sea ice volume loss is much more dramatic than sea ice coverage. A melted (warmer) ocean means more water from glaciers on land. This is the big unknown on sea level rise, but not hard to see where it is heading.
See Fig from arctic sea ice news:
http://nsidc.org/images/arcticseaicenews/20110816_Figure5.png
Recent (Feb 2012) evidence of impending breakoff of huge iceberg (hundreds of sq km) in the antarctic is another sign that we may be about to see big changes in sea level rise.
None of this was considered in the last IPCC report ...it will be in the next one.
Recent sea level rise is much faster
I believe the 1.8mm per year is the 20th century average.
The last 20 years it's been more like 3.1mm per year. http://www.cmar.csiro.au/sealevel/sl_hist_last_15.html
The Wikipedia article on the matter also suggests that the average for the past 3,000 years is more like 0 to 0.5mm per year, so it seems like it's speeding up considerably over the past century or two.
It has slowed down over the past year or so - due to the enormous amount of rainfall over land that occurred last year in Australia, South America, and a few other places. The same gravity satellites that are used to monitor the mass of the ice sheets detected a significant increase in mass over those areas. That water will eventually drain back in the oceans, though.
How much ice is swelling the sea?
If I understand correctly, the annual rise in sea level is 1.8mm per year. To suggest that this would fill Lake Erie eight times over or cover the US by a foot and a half of water is neither here nor there and presumably is inserted for shock value. At 1.8 mm per year it would take 50 years for sea level to rise by 9 cm, or 3.54 inches, an increase which hardly presages Armageddon.
Thats..... an interesting
Sorry I thought that went direct this was aimed FTO Andrew
Water-front real estate
Flannery and Gore better sell their waterfornt home quck smart before they become worthless.
Himalayan Glaciers
Have also stopped losing ice over the last 10 years !
http://www.foxnews.com/scitech/2012/02/09/himalayan-glaciers-have-lost-no-ice-in-past-10-years-new-study-reveals/
Thats an ..interesting.. interpretation of the facts
This statement that is, " the water has been inching up about as twice as fast lately". Thats not actually in the report, and its not even true. The rate has been constant. If there is a trend, its been slowing not increasing. Its been reported lots of places. .