New study last week threw a curve into our understanding of Antactic ice loss. Good discussion ongoing over at Stefan Rahmstorf’s facebook page. Stefan leads off with :
Interesting new study – if this holds up, then Antarctica is still gaining mass since the end of the last Ice Age due to increased snowfall. And modern global warming has caused ice loss, but not yet enough to tip the overall balance. If the latter turns out to be true, we have a problem of understanding the contributions to the observed modern sea-level rise. If less (or none) is coming from Antarctica, more must be coming from other sources.
Complicated issue, sure to be distorted by deniers. Let’s keep it simple.
What no one is arguing about is that sea level is rising, and that water is coming from somewhere.
So, as Dr. Rahmstorf mentions, the argument here is a bit of an ongoing shell game of trying to figure out exactly where this new water is coming from – whether from Greenland, Antarctica, or ongoing thermal expansion of oceans. This entails teasing some fairly faint signals out of complex data.
But wait, there’s more:
A new NASA study found that Antarctica has been adding more ice than it’s been losing, challenging other research, including that of the UN’s Intergovernmental Panel on Climate Change, that concludes that Earth’s southern continent is losing land ice overall.
In a paper published in the Journal of Glaciology on Friday, researchers from NASA’s Goddard Space Flight Center, the University of Maryland in College Park, and the engineering firm Sigma Space Corporation offer a new analysis of satellite data that show a net gain of 112 billion tons of ice a year from 1992 to 2001 in the Antarctic ice sheet.
That gain slowed to 82 billion tons of ice per year between 2003 and 2008.
Zwally and his colleagues used data on the changing height of the ice-sheet surface from the European Space Agency’s European Remote Sensing radar satellite between 1992 and 2001, and from NASA’s ICESat laser-ranging satellite between 2003 and 2008.
A question that arises is, how does this square with more recent, satellite based studies that have indicated Antarctica as a whole is losing mass?
During the past decade, Antarctica’s massive ice sheet lost twice the amount of ice in its western portion compared with what it accumulated in the east, according to Princeton University researchers who came to one overall conclusion — the southern continent’s ice cap is melting ever faster.
The researchers “weighed” Antarctica’s ice sheet using gravitational satellite data and found that from 2003 to 2014, the ice sheet lost 92 billion tons of ice per year, the researchers report in the journal Earth and Planetary Science Letters. If stacked on the island of Manhattan, that amount of ice would be more than a mile high — more than five times the height of the Empire State Building.
The vast majority of that loss was from West Antarctica, which is the smaller of the continent’s two main regions and abuts the Antarctic Peninsula that winds up toward South America. Since 2008, ice loss from West Antarctica’s unstable glaciers doubled from an average annual loss of 121 billion tons of ice to twice that by 2014, the researchers found. The ice sheet on East Antarctica, the continent’s much larger and overall more stable region, thickened during that same time, but only accumulated half the amount of ice lost from the west, the researchers reported.
“We have a solution that is very solid, very detailed and unambiguous,” said co-author Frederik Simons, a Princeton associate professor of geosciences. “A decade of gravity analysis alone cannot force you to take a position on this ice loss being due to anthropogenic global warming. All we have done is take the balance of the ice on Antarctica and found that it is melting — there is no doubt. But with the rapidly accelerating rates at which the ice is melting, and in the light of all the other, well-publicized lines of evidence, most scientists would be hard pressed to find mechanisms that do not include human-made climate change.”
My take is that there’s less here than this week’s headlines suggest. My first interview with Eric Rignot, in 2012, comes to mind, as he did a pretty good job of listing the various ambiguities in determining what’s going on in an area so large, and poorly observed, as Antarctica. You’ll hear him mention “IMBIE” (Ice Sheet Mass Balance Comparison Exercise) near the beginning – which is a cooperative effort among global researchers looking at ice melt, and has been the gold standard thus far insofar as credibility on this issue.
The results of the IMBIE 2012 experiments showed that the agreement between mass balance estimates from radar and laser altimetry, gravimetry and the input-output method is good in all ice sheet regions.
In combining the datasets we generated a 19 year time series of ice sheet mass balance from 1992 to 2011. Over this period, we found that the Greenland and Antarctic Ice Sheets together lost mass that equated to a global rise in sea level of 11.1 +/- 3.8 millimetres.
Examining the ice sheet regions individually we show that the Greenland, West Antarctic and Antarctic ice sheets have all lost mass over the past two decades, whilst the East Antarctic ice sheet has undergone a slight snowfall-driven growth. The Greenland ice sheet has lost the largest mass and accounts for about two-thirds of the combined ice sheet loss over the study period. In Antarctica, the largest mass losses have occurred in the West Antarctic Ice Sheet. However, despite occupying just 4% of the total ice sheet area, the Antarctic Peninsula has accounted for around 25% of the Antarctic mass losses
I thought the numbers were actually worse than these. The old numbers were 2 mm per year for the previous century which amounts to 20 cm or 8 in. The new numbers are an average 1.7 mm from 1870 to 2004. However, the averages for the past decade from satellite measurements is 3.3 mm which is double for all intents and purposes. This recent doubling is proof that the problem is recent while only getting worse.
https://en.wikipedia.org/wiki/Sea_level_rise
More from the IMBIE report—–“Overall our time series of mass change show that the combined losses from Greenland and Antarctica have increased over time and the ice sheets are now losing almost three times as much ice as they were in the early 1990’s”. And what, pray tell, is the correlation-causation there?
IMO, extrapolations, interpolations, and projections from satellite data from 1992-2001 don’t cut it when compared to the more recent GRACE data. I smell a bit of cherry picking and even “there has been no temperature rise (ice loss) for 18 years” type BS. Yes, the deniers will try to make something of this, and we will lose more time while we contemplate our navels. Too bad.
I’m not sure I get this. Are we losing “old” ice from the ice sheet while gaining it from snowfall?
That’s what this appears to say—-“Since 2008, ice loss from West Antarctica’s unstable glaciers doubled from an average annual loss of 121 billion tons of ice to twice that by 2014, the researchers found. The ice sheet on East Antarctica, the continent’s much larger and overall more stable region, thickened during that same time, but only accumulated half the amount of ice lost from the west, the researchers reported”.
And the key part is that the total amount that was gained in East Antarctica from snowfall was HALF the amount lost in West Antarctica and the Antarctic Peninsula (which is one of the places that is warming most rapidly on the entire planet).
The CU Sea Level Research Group sea-level time-series plot shown in this article is dated 10/16/2015.
Compare that plot with the 5/5/2015 version, shown here: http://sealevel.colorado.edu/content/2015rel1-global-mean-sea-level-time-series-seasonal-signals-removed
that’s quite a spike. what lesson do we draw from that?
That SLR is continuing to rise and even accelerating a bit in 2015?
That the 3.3mm per year rate may have to be revised upward if the new rate of increase holds?
That we will continue to dither and debate about “ambiguities” until large areas of coastline go under?
That we will then argue about why no one saw it coming and point fingers?