Guest “geological perspective” by David Middleton
CRYOSPHERE RESEARCH UPDATE
Unprecedented ice loss is predicted for Greenland Ice Sheet
30 Sep 2020
Over the next eighty years global warming is set to melt enough ice from the Greenland Ice Sheet to reverse 4000 years of cumulative ice growth – with rates of ice-loss more than quadruple even the fastest melt rates during the past 12,000 years. These stark conclusions come from new simulations which, for the first time, put current and projected future rates of ice-loss into context; comparing them directly with historical rates of ice-loss. These latest results are consistent with previous research that shows that if we continue our current high trajectory of greenhouse gas emissions we can expect Greenland to become ice-free in as little as 1000 years.
But as their simulation ventured into the future they discovered that the rate of ice-loss is likely to dwarf anything seen in the past. Under a high-emissions “business as usual” scenario Briner and his colleagues show that ice loss could reach an eye-watering 35,900 billion tonnes per century by 2100, whilst under a low-emissions scenario it is likely to rise to around 8800 billion tonnes per century. “It was a shocking to me to see that even with low emissions the pace of ice loss is going to be faster than it was during the warmest period in the past,” says Briner, whose findings are published in Nature.
A read-only copy of the paper is available for viewing… Nature.
Basically, RCP8.5 melts all of Greenland’s ice within 1,000 years.
Is anyone else picking up a “been there, done that” vibe?
This section adapted from The Insignificance of Greenland’s Ice Mass Loss in Five Easy Charts…
I downloaded the Kobashi et al., 2017 climate reconstruction from NOAA and plotted it to evaluate the context of recent climate change in central Greenland.
The inescapable conclusion is that if there ever was a climate “crisis,” it was during the Little Ice Age… It was FRACKING cold back then!
How does the recent melting compare to the rest of the Holocene? Short answer: “Same as it ever was”. Vinther et al., 2009 reconstructed the elevations of four ice core sites over the Holocene. There has been very little change in elevation of the two interior ice core sites (NGRIP and GRIP), while the two outboard sites (Camp Century and DYE3) have lost 546 and 342 m of ice respectively.
Vinther’s elevation reconstruction runs from 11,700 to 40 years before the year 2000. So the most recent year is 1960.
Based on the mass balance estimates from Mouginot, there was very little net change from 1960 to 1995, the starting year for Polar Portal’s elevation change maps. I enlarged the elevation change maps and posted the ice core locations on them.
The scale is in meters per year. Note that there has been very little change in ice elevation at these locations. Using my Mark I eyeball, I estimated the annual changes in elevation from 1995-2017.
Using the 2009 elevations provided by Vinther, I calculated the elevations of the four locations from 11,700 years ago up to 2017.
But, but, the Greenland ice sheet is still shrinking! When it all melts, sea level will rise by 7 meters!!!
We petroleum geologists are obsessed with calculating volumes of oil and gas reservoirs and we spend a lot of time making things called “isopach maps” and running “volumetrics“. Fortunately for me, Eric Gaba – Wikimedia Commons user: Sting made an isopach map of the Greenland ice sheet.
Almost all of the recent thinning is in the outboard areas of the ice sheet (“Same as it ever was”). I downloaded a high-resolution copy of the isopach map and digitized the contours using NeuraMap volumetric analysis software. The area and volume of the isopach map were inline with estimates in USGS Professional Paper 1386–A, Table 2, page A77.
- Area: 1,736,095 km2
- Volume: 2,600,000 km3
I used the 10 m contour as the 0 contour. The area of the 0 m contour was very close to the USGS area.
The volume was a little higher than the USGS estimate; but well within the range of other recent estimates. The USGS cites a 1954 reference for this number and also cites Bamber et al., 2011, which puts the volume at 2,900,000 km3. Bamber has subsequently upped his estimate to 2,960,000 km3.
As can be seen, estimates for the volume of the Greenland ice sheet vary widely and the methods of volumetric calculation yield a pretty wide range of results… Yet modern climate “scientists” can detect 0.015% annual changes in its mass… Go figure!
This is what happens if I drop the 1,000 m contour by 10 m:
|Method||Lose 10 m|
99.93% of the Greenland ice sheet doesn’t melt and/or calve into the ocean. The USGS paper states that if the entire ice sheet were to melt, sea level would rise by 6.5 meters. In the highly unlikely scenario above, sea level would rise by a whopping 4.8 mm.
- 6.5 m * 0.07% = 0.00478 m
What happens if I drop the 1,000 m contour by 100 m?
|Method||Lose 100 m|
- 6.5 m * 0.82% = 0.0531m
That’s just over 2 inches of sea level rise.
RCP8.5: Junk Science on steroids
If you review their paper in Nature, you’ll see that the nightmare scenarios are all ginned up with the RCP8.5 model scenario, the one where Doctor Evil melts the icecaps with a space “laser.”
This section adapted from: U.S. Climate Resilience Tool Kit: Greenland Stays Frozen in 2100… Even Under RCP8.5
I stumbled across something very useful yesterday on Climate-Dot-Gov’s U.S. Climate Resilience Tool Kit page.
The widget generates CMIP5 or PMIP3 model outputs for specific countries and a temperature change map of the world. You can also spit out plots of each model. And these outputs display the actual temperature ranges rather than anomalies.
Since Greenland is such a great climatic playground, I started playing around with it.
Greenland Stays Frozen in an RCP8.5 Bad Science Fiction Nightmare
The first thing I did was to hit Greenland with RCP8.5.
While the histogram indicates a 5.1 °C rise in the average annual surface temperature. It’s thought that the Sangamonian (Eeemian) interglacial was at least 5 °C warmer than today and Greenland retained much of its ice. However, most of that 5.1 °C rise appears to be in winter and the average July temperature is projected to still be below freezing, only 2-3 °C warmer than the 1980-2004 mean.
Andy May’s brilliant analysis of NCA4 featured this image:
Andy noted the following:
INM-CN4 is labeled and it, alone, is tracking the observations with enough accuracy, yet it does not predict dangerous temperatures in the future or any significant human influence on climate.
This drew some standard ad hominem and/or unsupported dismissals of Dr. Christy’s work and derision of INM-CM4. So I downloaded UAH 6.0 and HadCRUT4 and plotted 5-yr running means at the same scale as Dr. Christy’s 2016 plot.
UAH 6.0 generally plots within 0.1 °C of the average of 3 satellite datasets, closest to INM-CM4. HadCRUT4 plots well-below the model-mean closest to the only model that runs hotter than INM-CM4. Note that there’s not a lot of difference between HadCRUT4 and UAH 6.0. (0.1-0.2 °C is not a lot of difference).
Here are the RCP8.5 and RCP 4.5 outputs for INM-CM4 in Greenland:
Both models indicate that Greenland won’t be significantly warmer in 2100 than it was in 1850. Almost all of the warming comes from an increase in the minimum temperatures.
1850 was very cold by Holocene standards.
Where is Inigo Montoya when you need him?
Tipping Points: “You keep using that [phrase], I do not think it means what you think it means”
The Physics World article closes with this…
Previous research has suggested that we have already passed the point of no return for the Greenland Ice Sheet, with no hope of preventing a complete meltdown, but Briner and his colleagues are not convinced that this tipping point has passed. “It is clear that we are now committed to a lot of ice loss through this century, but our simulation shows that if we follow a low-emissions pathway the rate of ice-loss may slow as we approach 2100. It is possible to leave future generations with a healthy Greenland Ice Sheet,” he says. Lenton concurs and thinks there is still time to act. “Even if tipping points have been passed, because the ice sheet dynamics are relatively slow, it is possible to ‘overshoot’ an ice sheet tipping point temporarily and still recover the situation. That of course requires bringing greenhouse gas levels down, which is going to require deliberate greenhouse gas removal on top of stopping greenhouse gas emissions.”Physics World
There you have it… The bear will always remain just out of sight in the woods.
A couple of weeks ago a massive chunk of ice – equivalent in size to the Caribbean island of Montserrat – broke away from north-east Greenland.Physics World
Montserrat ~ 2 Mahattans
Manhattan-sized Icebergs are insignificant relative to Greenland-sized ice sheets.
- Manhattan: 34 square miles.
- Greenland ice sheet: 660,235 square miles.
Manhattan = 0.005% of Greenland ice sheet. 99.995% of the Greenland ice sheet did not participate in this event.
If one Manhattan-sized chunk of ice calved into the ocean every year and there was no snow accumulation in Greenland for 1,000 years, Greenland would lose 5% of its ice sheet. A little perspective on Manhattan-sized chunks of ice…