There’s some blogospheric carping about his statement in the JPL press release below regarding Greenland’s ice sheets:“… their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050.”
Well sure, it could be, but as this recent surprise study from GISS’s neighbors at Columbia illustrates, even though we’ve had the GRACE (Gravity Recovery And Climate Experiment) satellite looking at Antarctica, and concluding there’s been ice mass loss there, we have this new study that shows ice being added from underneath due to meltwater refreeze, concluding the models to be wrong.
It goes to demonstrate that we really don’t understand ice sheet mechanics well enough yet to make accurate forecasts, though some people think we can.
Add to that, GRACE has it’s own set of problems. And at least one model conlcusion has been revised post facto because the melt data is overestimated:
The melting of the ice sheets of Greenland and West Antarctica is about twice as slow as previously thought. The study, conducted by TU Delft, SRON and the Jet Propulsion Laboratory. The scientists published their findings in the September issue of Nature Geoscience.
We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted.’ The average rise in sea levels as a result of the melting ice caps is also lower.
In fact, errors from GRACE may be quite large. So take this new release from JPL and the squawking about the forecasted sea level rise with a grain of salt. But more importantly, look at what the actual sea-level data is saying, and as Willis Eschenbach points out, natures seems to be Putting the Brakes on Acceleration.
From JPL: NASA Finds Polar Ice Adding More to Rising Seas
Store Glacier, West Greenland. A new NASA funded study finds that the Greenland and Antarctic ice sheets are losing mass at an accelerating pace, three times faster than that of mountain glaciers and ice caps. Image credit: Eric Rignot, NASA JPL
PASADENA, Calif. — The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new NASA-funded satellite study. The findings of the study — the longest to date of changes in polar ice sheet mass — suggest these ice sheets are overtaking ice loss from Earth’s mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much sooner than model forecasts have predicted.
The nearly 20-year study reveals that in 2006, a year in which comparable results for mass loss in mountain glaciers and ice caps are available from a separate study conducted using other methods, the Greenland and Antarctic ice sheets lost a combined mass of 475 gigatonnes a year on average. That’s enough to raise global sea level by an average of 1.3 millimeters (.05 inches) a year. (A gigatonne is one billion metric tons, or more than 2.2 trillion pounds.)
The pace at which the polar ice sheets are losing mass was found to be accelerating rapidly. Each year over the course of the study, the two ice sheets lost a combined average of 36.3 gigatonnes more than they did the year before. In comparison, the 2006 study of mountain glaciers and ice caps estimated their loss at 402 gigatonnes a year on average, with a year-over-year acceleration rate three times smaller than that of the ice sheets.
“That ice sheets will dominate future sea level rise is not surprising — they hold a lot more ice mass than mountain glaciers,” said lead author Eric Rignot, jointly of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Irvine. “What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise.”
Rignot’s team combined nearly two decades (1992-2009) of monthly satellite measurements with advanced regional atmospheric climate model data to examine changes in ice sheet mass and trends in acceleration of ice loss.
The study compared two independent measurement techniques. The first characterized the difference between two sets of data: interferometric synthetic aperture radar data from European, Canadian and Japanese satellites and radio echo soundings, which were used to measure ice exiting the ice sheets; and regional atmospheric climate model data from Utrecht University, The Netherlands, used to quantify ice being added to the ice sheets. The other technique used eight years of data from the NASA/German Aerospace Center’s Gravity Recovery and Climate Experiment (Grace) satellites, which track minute changes in Earth’s gravity field due to changes in Earth’s mass distribution, including ice movement.
The team reconciled the differences between techniques and found them to be in agreement, both for total amount and rate of mass loss, over their data sets’ eight-year overlapping period. This validated the data sets, establishing a consistent record of ice mass changes since 1992.
The team found that for each year over the 18-year study, the Greenland ice sheet lost mass faster than it did the year before, by an average of 21.9 gigatonnes a year. In Antarctica, the year-over-year speedup in ice mass lost averaged 14.5 gigatonnes.
“These are two totally independent techniques, so it is a major achievement that the results agree so well,” said co-author Isabella Velicogna, also jointly with JPL and UC Irvine. “It demonstrates the tremendous progress that’s being made in estimating how much ice the ice sheets are gaining and losing, and in analyzing Grace’s time-variable gravity data.”
The authors conclude that, if current ice sheet melting rates continue for the next four decades, their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050. When this is added to the predicted sea level contribution of 8 centimeters (3.1 inches) from glacial ice caps and 9 centimeters (3.5 inches) from ocean thermal expansion, total sea level rise could reach 32 centimeters (12.6 inches). While this provides one indication of the potential contribution ice sheets could make to sea level in the coming century, the authors caution that considerable uncertainties remain in estimating future ice loss acceleration.
Study results are published this month in Geophysical Research Letters. Other participating institutions include the Institute for Marine and Atmospheric Research, Utrecht University, The Netherlands; and the National Center for Atmospheric Research, Boulder, Colo.
JPL developed Grace and manages the mission for NASA. The University of Texas Center for Space Research in Austin has overall mission responsibility. GeoForschungsZentrum Potsdam (GFZ), Potsdam, Germany, is responsible for German mission elements.
More on Grace is online at http://www.csr.utexas.edu/grace/ and http://grace.jpl.nasa.gov/ .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
===========================================================
Here’s the paper abstract at GRL:
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L05503, 5 PP., 2011
doi:10.1029/2011GL046583
Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise
E. Rignot
Earth System Science, University of California, Irvine, California, USA
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
I. Velicogna
Earth System Science, University of California, Irvine, California, USA
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
M. R. van den Broeke
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
A. Monaghan
National Center for Atmospheric Research, Boulder, Colorado, USA
J. Lenaerts
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time-variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.
Received 4 January 2011; accepted 2 February 2011; published 4 March 2011.
Citation: Rignot, E., I. Velicogna, M. R. van den Broeke, A. Monaghan, and J. Lenaerts (2011), Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise, Geophys. Res. Lett., 38, L05503, doi:10.1029/2011GL046583.
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From R. Gates on March 10, 2011 at 4:54 pm:
Thus you’re 75% “warmist”, and 25% scientifically-minded?
That would explain so much…
My son has reviewed his high school class on “the impact of climate change”. His teacher asserts that the seas will rise twenty feet or so and that the Arctic ice will disappear by 2050.
Theo Goodwin says:
March 10, 2011 at 5:43 pm
R. Gates says:
March 10, 2011 at 4:54 pm
I see your problem. Your time periods are way too short for the purposes of science.
_____
Hardly. But you also make the inaccurate assumption that science is only concerned with some specific time period…which is of course absurd. From nanoseconds to billions of years, science is concerned with it all and so there is no specific time period that is ‘way too short” for the purposes of science.
Now then, in regards to climate, once more, we see that science is concerned with all sorts of time scales…from the very short time period that LW radiation is absorbed and then re-emitted by the CO2 molecule, to the hundreds of millions of years that it takes our solar system to make a complete revolution about the core of the Milky Way…these vastly different time scales can have different effects on our climate. Zeroing in on the anthropogenic effects of CO2…one might imagine that science might want to look back at the history of CO2 in our atmosphere…especially when they can see exactly what it was, such as found in ice cores, but especially just prior to the rapid increase in CO2 beginning with the industrial revolution. Since that time, CO2 has increased some 40%, and so, science might want to study very closely what the expected natural variations the climate would be in that time frame up to the present…so over a few centuries down to a few decades. Especially significant would be the changes in climate over the past century or so as anthropogenic CO2 has really taken off.
So to suggest that climate science, or any science for that matter, should be concerned with some particular time scale is really quite silly…it just depends on what kind of effects you’re interested in studying…i.e. over what time scale are they likely to be seen.
I’ve said time and time again that if you want to consider sea-level rises then the key is to look at the impact. Where is the land that the globe is losing to these rapidly rising sea levels? Take a small island like the UK – how can we see how much land has been lost to the sea? Well for the last 50years or so we have accurate photographs taken for map purposes that would show exactly how much land we have lost to the sea over that period. Going further back we have accurate maps of the coast from the Navy that can be used to determine where the coastline is relative to certain unmoving landmarks such as lighthouses. Most of the UK is nowhere near the coast, so in percentage terms such measurements would give us land lost to the sea in those small areas at the coast to extraordinary precision.
Having done this already for Bangladesh in a simple way, the simple truth is that this low-lying nation has actually got bigger over the last 50 years and not smaller as TeamAGW would have us believe.
Ice breakup occurs at the edge of every ice sheet and glacier. It is normal because ice needs support from all sides and when the ice gets to the end of its travel is is not supported so it breaks up. But it is replaced by snow falling upslope/inland. This has to happen or the sheet or glacier would be very short lived. Kilimanjaro has lost ice cover because of lack of precipitation not rising temperatures. Temperatures there have remained doggedly below zero.
So does this new study take into account ice replacement by precipitation? I suspect not since this is a difficult if not impossible task. Without this vital information any ice loss data is meaningless and open to alarmist claims.
[snip – over the top – anthony]
As for the AGW/CAGW believers, apparently by disagreeing
1) you can’t show them the data is bad,
2) the interpretations are biased or inappropriate, and
3) the models on which their projections are inadequate.
By agreeing, apparently you can’t
4) show that their projections must have huge footprints right now, and
5) there is no evidence for the extreme things that must be happening right now.
We are in the same position as thoe at the latter end of the witch trials of the 13th through 17th century: the learned and self-thinking could not stop witch-mania, or even witch-hunting. For a while they succeeded in stopping the persecution by stopping the funding of witch-hunters, judges, cities, church and state by the sale of assets held by the “witches”. (Contrary to popular understanding, a great many rich and noble families were destroyed as witches.) It didn’t work all that well, as the political powers worked out a mutually beneficial way to split the profits and so get back into business.
Ultimately all those opposed to the witchcraft hysteria could do was, at great personal peril, stop specific “witches” from being burnt or hanged by appeal to the local jury. Over time the locals came to see that not just distant strangers but everyone was coming under suspicion – personal friends and families known by them to be innocent. And that their trial was surely coming. That was when the persecutions stopped: the absurdity of the state’s obsession with witchcraft had become a personal threat.
For climate change/whatever, we’ve gone through arguing against and with. De-funding is upon us. The final stage will be when”green” taxes and regulations stretch to make everything everyone enjoys unattainable. Bluntly put, what will really end the current mania is a carbon-tax of $3 on a bottle of beer, as beer has (or generates) CO2. Then this foolishness will stop. Let’s ask a congressman from Utah to help.
R. Gates, you state in regard to natural variables:
“Those other explanation include:
1) Unknown solar effects
2) Unknown ocean cycles
3) Unknown astronomical effects”
What is your opinion on the role of land use changes as documented by Pielke Snr. and others?
http://pielkeclimatesci.files.wordpress.com/2009/10/r-198.pdf
Also, by stating – in regards to what evidence would make you more ardent in your belief of AGW -that:
“in fact [I] look for continued glacier, ice cap, and sea ice decline…”
you appear to be exhibiting a confirmatory bias toward AGW which will probably render any objective reading of alternate possibilities unlikely. I mention this from personal experience. In the not so distant past I was not 75 percent but 110!
best wishes, ian
Anthony Watts says:
Well sure, it could be, but as this recent surprise study from GISS’s neighbors at Columbia illustrates, even though we’ve had the GRACE (Gravity Recovery And Climate Experiment) satellite looking at Antarctica, and concluding there’s been ice mass loss there, we have this new study that shows ice being added from underneath due to meltwater refreeze, concluding the models to be wrong.
You are creating a false dichotomy here.
The meltwater refreeze doesn’t contradict the GRACE data on mass balance. Whether we are looking at ice mass or ice volume, the numbers will be the same if there is meltwater underneath portions of the ice sheet on land or whether this is refrozen. If it is under the ice cap, it is counted as ice volume or mass.
There is no ice being added there. It is just changing its location from the top to the bottom of the ice sheet.
John Marshall says:
March 11, 2011 at 2:30 am
Ice breakup occurs at the edge of every ice sheet and glacier. It is normal because ice needs support from all sides and when the ice gets to the end of its travel is is not supported so it breaks up. But it is replaced by snow falling upslope/inland. This has to happen or the sheet or glacier would be very short lived. Kilimanjaro has lost ice cover because of lack of precipitation not rising temperatures. Temperatures there have remained doggedly below zero.
Kilimanjaro is not a typical mountain glacier. Don’t use it as a prototype example.
The ice on Kilimanjaro is disappearing because of sublimation, rather than melting.
So does this new study take into account ice replacement by precipitation? I suspect not since this is a difficult if not impossible task. Without this vital information any ice loss data is meaningless and open to alarmist claims.
Your suspicion is wrong. All you have to do is read to find this out.
The new study as described uses two methods of measurement. One looks at ice losses and gains, and the other looks at change in mass, which is the result of gain minus loss.
The study compared two independent measurement techniques. The first characterized the difference between two sets of data: interferometric synthetic aperture radar data from European, Canadian and Japanese satellites and radio echo soundings, which were used to measure ice exiting the ice sheets; and regional atmospheric climate model data from Utrecht University, The Netherlands, used to quantify ice being added to the ice sheets. The other technique used eight years of data from the NASA/German Aerospace Center’s Gravity Recovery and Climate Experiment (Grace) satellites, which track minute changes in Earth’s gravity field due to changes in Earth’s mass distribution, including ice movement.
ian says:
March 11, 2011 at 7:19 pm
R. Gates, you state in regard to natural variables:
“Those other explanation include:
1) Unknown solar effects
2) Unknown ocean cycles
3) Unknown astronomical effects”
What is your opinion on the role of land use changes as documented by Pielke Snr. and others?
http://pielkeclimatesci.files.wordpress.com/2009/10/r-198.pdf
Also, by stating – in regards to what evidence would make you more ardent in your belief of AGW -that:
“in fact [I] look for continued glacier, ice cap, and sea ice decline…”
you appear to be exhibiting a confirmatory bias toward AGW which will probably render any objective reading of alternate possibilities unlikely. I mention this from personal experience. In the not so distant past I was not 75 percent but 110!
best wishes, ian
_______
First, land use changes certainly play a role in the overall anthropogenic influence on climate. The Pielke Sr. et. al. study was really looking a regional climate influences from local land uses, and then, to a lessor extent, comparing these effects to the influence from the general global increase in CO2.
This study is interesting and really not at all surprising in its findings. Land use changes ought to cause regional climate changes, and one might expect these to be stronger (over some specified period) than the year-to-year increase in CO2 since the 1700’s. When looking at CO2, one must not look at the short-term year to year, or even decade to decade changes, but one must look at the CUMULATIVE change brought about by a 40% increase in CO2 since the 1700’s. From a geological and historical perspective, this 40% increase over a few hundred years represents a sudden spike in CO2, and nothing like this has happened in at least 800,000 years. I’ve likened this event to a human caused CO2 volcano that continues to erupt (i.e. we are 40% higher in CO2 and RISING).
Now, unlike many on this blog, I happen to have a great amount of respect for the sophistication and complexity of GCM’s and though I fully recognize that they are far from perfect, and will never get the exact details correct, I think they are very good at telling us trends. Their prediction, for example, of the first signs of global warming being seen in the Arctic, is right on target. Skeptics will poo-poo this and claim it is just natural variation, all happened before, etc., but I believe these skeptics don’t, won’t, or can’t fully appreciate how well the GCM’s agree on this, why they agree, and why the Arctic is generally responding as forecast (though perhaps even faster).
Aside from my belief that GCM’s generally have the trends correct (though the chaotic nature of the climate system will prevent them from every getting the details or even tipping points correct), everyday it seems new confirmatory research comes out that further validates the general tenets of AGW theory. For example, this study:
http://www.physorg.com/news/2011-03-earth-core-climate-insights.html
This is powerful confirmatory evidence that the GCM’s are generally right in the causes and trends they use in their scenarios.
I’ve stated many times what it would take for me to move my position from 75/25 warmist/skeptic. So far, I’ve seen very little evidence to move me more toward the skeptics camp, and more that would tend to move me more toward the warmist. I agree though, that there is a danger in having a jaded eye when reviewing alternative thought, but that’s a danger we all face from whatever position we have on any issue.
This summer’s Arctic sea ice looks to be falling very close to what we saw in 2007. If this happens- to what will the AGW skeptics attribute it? Their much beloved hero Joe Bastardi is expecting a higher summer low much higher than last year based on long term ocean cycles. If this doesn’t happen as Joe forecasts, but in fact we see a summer low hitting closer to 2007 or even lower, what new hypothesis will the AGW skeptics cling to? On the other hand, if the summer Arctic sea ice does indeed begin to rebound over the next few decades, then that single piece of evidence will be contrary in trend to every GCM forecast and would cause me to doubt the AGW theory greatly.
showing
RG;
Warming is not AGW. If the Arctic is ice-free for the next 10 Julys, it means nothing about CO2.
And it will/would be great for shipping.
But we’re into the cool half of the 60-yr cycle now, and there’s no hope of that.
@Tom Konerman
The data is available at CSIRO from Dec. 30th 1992 up to Dec. 30th 2010. It’s been there for quite some time now. I’ve seen that comment post many time of multiple blogs, but the data is there. I don’t know why people are saying the data isn’t there. Is it the data or some other product reprenting the data ?