Sunday, March 16, 2014

Media claims that "Greenland's ice loss has tripled in a decade" are CAGW propaganda

The CAGW alarmist media is awash today with claims based on a paper published in Nature Climate Change that "Greenland's ice loss has nearly tripled in a decade" and "the Greenland ice sheet has lost it's last grip." As usual, the paper has been hyped by the media to portray impending doom, while examination of the actual scientific paper reveals very little of concern.

Figure 1a shows the tiny region of Greenland that the paper studied, with a blowup of this region in figure 2 below. The authors find an increase in the natural glacier calving process in this regional, relatively tiny portion of the Greenland ice sheet. According to the authors, this is due to regional warming found at the site "HKH" marked by an "X" in fig. 2a below. The key word here is regional, which indicates these processes are localized and not characteristic of global warming. In fact, the authors also looked at another nearby site "DH" marked by an "X" in fig. 2a below and found that this site cooled over the past decade.

Examination of Figure 2 below reveals that over the past 34 years 1978-2012:

Annual sea surface temperature anomaly has cooled at both sites DH and HKH
June-August summer temperatures sswarmed at site HGH but cooled at site DH, and are only about 2C above the freezing point
Annual air temperatures at both sites increased, but are about 10 degrees cooler than the freezing point

These localized, regional changes were not predicted by climate models and are not supportive of the CAGW meme, and in fact suggest that other processes are responsible. For example, geothermal sources have recently been discovered under the Greenland ice sheet, which create lakes under the ice sheet and lubricate the natural slide to calving in the ocean. In addition, storm activity and winds largely control Arctic sea ice, which can act as an impediment to glacier calving.

Figure 2:

A few of the alarmist articles published on this paper today:

Greenland’s Ice Loss Triples and Raises Global Warming Awareness

Fears of faster rising global sea levels as 'stable' Greenland ice sheet starts to melt

Greenland's ice loss nearly tripled in a decade USA TODAY A formerly stable part of Greenland's ice sheet in the northeast has been losing ice at an accelerating rate.

Regional warming triggers sustained mass loss in Northeast Greenland ice sheet

Greenland Ice Sheet Loses Its Last Grip

Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming

Nature Climate Change (2014) doi:10.1038/nclimate2161

Abstract

The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr⁻¹ of a total of 3.2 mm yr⁻¹. A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbræ) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future.

Introduction

Mass loss from the Greenland ice sheet (GrIS) is regionally distributed between sectors manifesting quite different sensitivities to external forcings^1, 2, 3. Enhanced surface melting and dynamic thinning associated with the speed-up of glacier flow¹ is mainly concentrated in the southest, west and northwest parts of the GrIS (refs 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14), where most of the ice margin is in contact with the ocean. In southwest Greenland, where the ice sheet margin is typically located up to 100 km inland, there are few marine-terminating glaciers and mass loss is dominated by atmospheric forcing¹. In contrast, major marine-terminating outlet glaciers characterize the northeast sector of Greenland, but these glaciers are surrounded by year-round sea ice, which suppresses calving front retreat¹⁵.

Many of the glaciers in southeast, west and northwest Greenland that experienced dynamic thinning in 2003 and 2005, respectively, have somewhat slowed down in recent years^7, 8, 16. However, the two glaciers with the largest contributions to GrIS mass loss—Jakobshavn Isbræ (JI) and Kangerdlugssuaq Glacier (KG)—have maintained their high rate of mass loss throughout the past decade¹¹ (Fig. 1a–c and Table 1). Both glaciers possess a negative bed slope^17, 18 (a bed that deepens inland) that lies below sea level, the key conditions for satisfying the marine ice sheet instability hypothesis associated with parts of west Antarctica^19, 20, 21. However, a far more substantive (by area) marine-based sector (Fig. 1) lies at the mouth of the >600-km-long northeast Greenland ice stream^22, 23, 24 (NEGIS), with its three main outlets, the Nioghalvfjerdsfjorden Glacier (NG) also called 79 North, the Zachariae Isstrøm (ZI) and Storstrømmen Glacier (SG) (Fig. 2a). NG is characterized by its almost 80-km-long and 20-km-wide floating tongue, widening to about 30 km at the calving front^{22, 23, 24, 25, 26}. ZI has an almost 30-km-long calving front and is grounded at present. Both glaciers are located at the northeastern corner of the GrIS near Fram Strait and the Nordic Sea and are exposed to ocean variability²². They both have fast (>1 km yr⁻¹) near-terminus velocities. SG is located about 200 km south of ZI and has a 20-km-wide calving front. However, SG diverges into two lobes, one which calves directly into the ocean, whereas the other merges with Bistrup Glacier (BG). Both lobes have slow (~100 m yr⁻¹) near-terminus velocities.

Figure 1: Changes in surface elevations obtained using ICESat, ATM, LVIS and ENVISAT data (Supplementary Section 1.0).

Table 1: Ice mass loss rates.

Full table

Figure 2: Surface speed, mass loss rates and climate data.

Here we use repeat measurements of surface elevation over the entire GrIS to estimate dynamic thinning at marine margins (Fig. 1a–c and Supplementary Section 1.0). Our results show that the NEGIS was relatively stable for at least a quarter of a century, followed by rapid dynamic thinning starting some time between 2003 and 2006. To investigate possible forcing mechanisms capable of triggering such instability, we analyse surface and subsurface water temperature, near-surface air temperature variations and sea ice concentrations

We map elevation changes from April 2003 to April 2012 using altimeter surveys from the National Aeronautics and Space Administration’s airborne topographic mapper (ATM) flights from 2003 to 2012 (ref. 27) supplemented with ice, cloud and land elevation satellite (ICESat) laser altimeter data from 2003 to 2009 (ref. 28), land, vegetation and ice sensor (LVIS) data from 2007 to 2012 (ref. 29) and European Space Agency Environmental Satellite (ENVISAT) data from April 2009 to March 2012 (ref. 30). To assess thinning before 2003, we produced a 25 × 25 m gridded digital elevation model using aerial photographs³¹ from 1978 that cover the coastal portion of the northeast sector of Greenland (Fig. 2a and Supplementary Section 3.1).

Ice-sheet-wide mass loss

Mass loss rates calculated for the entire GrIS reveal a dramatic increase in loss caused by surface mass balance (SMB) between April 2003 and April 2012, and a complex contribution from dynamic mass loss (Table 1).

The average ice-sheet-wide mass loss increased from 172.4 ± 21.7 Gt yr⁻¹ during April 2003–April 2006 to 359.8 ± 28.9 during April 2009–April 2012. The increase is due to a combination of increased dynamic mass loss and SMB-inferred mass loss. To estimate mass loss due to changes in ice dynamics, we subtract the SMB-inferred mass loss (obtained using the regional climate model RACMO2; ref. 32) from the observed mass loss rate. Dynamically driven mass loss rates increased from 129.7 ± 22.7 Gt yr⁻¹ during April 2003–April 2006, to 156.3 ± 40.9 Gt yr⁻¹ during April 2009–April 2012. This increase is mainly due to the acceleration of several outlet glaciers experiencing speed-up^4, 5, 8. However, cases of glacier slowdown are reported¹¹, for example, at Helheim Glacier (HG) where dynamically driven mass loss decreased from 7.0 ± 1.0 Gt yr⁻¹ during April 2003–April 2006, to −1.2 ± 1.2 Gt yr⁻¹ during April 2009–April 2012. The other two main outlet glaciers in south Greenland, JI and KG, have kept their high rate of dynamically driven mass loss (>10 Gt yr⁻¹) throughout the past decade. In north Greenland, the NEGIS basin has increased its contribution to dynamically driven mass loss to more than 10 Gt yr⁻¹ during April 2006–April 2012, a mass loss rate similar to JI after its speed-up in the late 1990s (ref. 33; Table 1). Estimation of ice flux rate for NG and ZI suggest an increase of ice flux by 9.8 ± 3.0 Gt yr⁻¹ during February–April 2011 relative to winter 2000–2001. The flux rate for ZI increased further in 2012 (Supplementary Table 4).

Thinning of the northeast Greenland ice sheet since 1978

The average ice surface elevation change rates for coastal portions of the NEGIS between 1978 and 2003 are displayed in Fig. 3a. The 1978 digital elevation model, based on aerial photographs, is limited to areas below the snow line (within roughly 100 km of the ice margin), because the low contrast over snow prevents data sampling. To estimate elevation change rates between 1978 and 2003, we use aerial photography from 1978 and ICESat data from 2003. Fig. 3a shows only minor elevation change rates during 1978–2003, suggesting this sector of the GrIS had been relatively stable for at least 25 years preceding 2003 (Table 1). This conclusion is further supported by sparse ATM data between 1995 and 1999 (Supplementary Section 3.1.2). Fig. 3b shows that this stable period was followed by relatively localized fluctuations in elevation change rates during April 2003–April 2006. However, more pervasive and pronounced thinning rates are observed from April 2006 to April 2009 (Fig. 3c) and continue uninterrupted throughout April 2009–April 2012 (Fig. 3d). Thinning rates of more than 1 m yr⁻¹ cover an area of 840 km² by April 2003–April 2006, 5,946 km² by April 2006–April 2009 and 7,747 km² by April 2009–April 2012. Fig. 3e, f shows SMB-induced thinning rates for the same periods as in Fig. 3a–d. The thickening from 2003 to 2012 on SG and BG (two dome-like features located 60–100 km upstream from the main glacier flow line) is probably due to the buildup of mass in their reservoir area following the surges of the two glaciers during 1978–1984 (refs 34, 35).

Figure 3: Surface elevation change rates in northeast Greenland using aerial photographs, ICESat, ATM, LVIS and ENVISAT data.

Accelerated mass loss associated with the NEGIS is further documented by continuous global positioning system (GPS) receivers established on bedrock to measure vertical surface displacement driven by the changes in ice loads³⁶. All stations in the northeast sector of the Greenland GPS Network³⁷ are uplifting owing to some combination of the Earth’s instantaneous elastic response to contemporary changes in ice mass and its delayed viscoelastic response to past changes in ice mass. However, accelerations in uplift can be attributed only to contemporary accelerations in ice mass losses. GPS data from 2008 to 2013 record accelerating uplift (Fig. 2a) caused by increasing mass loss centered at the front of ZI. Combined with the elevation data this strongly supports the conclusion that ZI mass loss has been accelerating since at least 2003 and was ongoing through 2013.

Acceleration and retreat

Fig. 4a, b shows positions of calving fronts at various times between 1978 and 2012. The 1978 calving front is obtained from aerial photos, whereas the 1999–2012 fronts are based on Land Remote-Sensing Satellite System images from http://glovis.usgs.gov andhttp://earthexplorer.usgs.gov. All images were recorded in July or August. The front of NG retreated by 5–7 km during 1978 and 2003, but was at more or less the same position between 2003 and 2009 (ref. 38). During 2009–2012 the southern tip and the mid-section retreated by 2–3 km. The retreat took place at the floating tip of the glacier. The frontal portion of ZI broke off during 2002. The break-off did not result in thinning, probably owing to low lateral resistance¹⁵. The ZI retreated in 2002 and caused minor thinning near the front. However, once the portion of the glacier that is in deeper water (Fig. 4c) started to retreat in 2005–2006 (Fig. 4b), the thinning rate increased. The glacier continued retreating, thinning and speeding up with an accelerating rate through 2012.

Figure 4: Calving front positions, bed and velocity profiles along the main flow line of NG and ZI.

To assess the dynamically induced thinning in northeast Greenland, we examine ice speeds during 2000–2012 along transect 1 and 2 (displayed as black lines in Fig. 4c). We use winter velocity maps for Greenland, derived using interferometric synthetic aperture radar (InSAR) data from the RADARSAT-1 satellite and the TerraSAR-X satellites, provided by the National Snow and Ice Data Center³⁹. Changes in ice speeds during winter 2005–2006, winter 2006–2007, winter 2007–2008, winter 2008–2009, February–April 2011 and March 2012, relative to winter 2000–2001, are displayed in Fig. 4d, e. Bed and ice surface elevation above sea level¹⁷ along transects 1 and 2 (displayed as black lines in Fig. 4c) are also shown in Fig. 4d, e. The two transects represent the main ice flow lines where the changes in ice speed are largest.

The floating tongue of NG increased its ice speed by 10–50 m yr⁻¹ during 2005–2009 relative to the winter 2000–2001 ice speed (Fig. 4d) and by more than 100 m yr⁻¹ in 2011 relative to winter 2000–2001. The calving front positions of NG and ZI in summer 2009 are located at a distance of 0 km for each transect plotted in Fig. 4d, e. Increased flow speeds of ZI started to migrate inland in winter 2008–2009 (Fig. 4e and Supplementary Fig. 14). During 2005–2006, 2006–2007 and 2008–2009 the winter speeds at distances above 70 km along the transect from Z1 to Z2 are more or less the same as that of winter 2000–2001. However, during winter 2008–2009 the speed at distances up to 150 km is larger than that of winter 2000–2001 (Supplementary Fig. 14). Velocities at the frontal portion of ZI resumed increase during February–April 2011 and suggest an increasing trend in velocity. However, it should be noted that we compare winter velocities. Summer velocities are likely to be larger.

Regional warming

Sea ice concentration for the month of September (typically the annual minimum) is displayed in Fig. 5 for 1979–2011. The data are derived using measurements from the Scanning Multichannel Microwave Radiometer on the Nimbus-7 satellite and from the Special Sensor Microwave/Imager sensors on the Defense Meteorological Satellite Program’s -F8, -F11 and -F13 satellites⁴⁰. The lowest monthly sea ice concentration in the fjord system located outside NG and ZI is observed in 2003, which probably caused the minor fluctuations in elevation change rates during April 2003–April 2006.

Annual mean sea surface temperature anomalies (Fig. 2d and Supplementary Information) show an increase in 2003, which coincides with the record low sea ice concentration in that year. Fig. 2e, fshows the five-year running mean annual and summer (June–August) near-surface air temperature at Henrik Krøyer Holme (HKH) and Danmarkshavn. Both weather stations are located at the coast close to sea level⁴¹. Summer temperatures increased by about 2 °C in 2003 (Fig. 2e) compared with 1978. The high summer temperatures probably helped to reduce the sea ice extent, causing a retreat of about 10 km of the ZI calving front around 2002–2003 (Fig. 4e), which reduced the back stress acting on the floating fronts of the glacier. The absence of sea ice was accompanied by changes in glacier elevation rates near the margin (Fig. 2b).

During 1978–2003, annual mean subsurface water temperature anomalies (Supplementary Section 4.1) were 0.0–0.3 °C higher than the 1961–1990 average (Fig. 2c). Inflow of large volumes of warmer water (0.5–0.8 °C) occurred about 2006–2007 (refs 42, 43), which probably enhanced the sea ice retreat and glacier thinning rate (Fig. 2).

Conclusions

Our analysis suggests that increased air temperature (spike in Fig. 2e) triggered the dynamically induced mass loss around 2003. The warm summer temperatures probably reduced sea ice concentration in 2002–2004 (Fig. 5) causing both glacier fronts to calve heavily and retreat around 2002–2004 (Fig. 4a, b). This reduced the back stress acting on the lower glaciers and caused acceleration that propagated upstream (Fig. 4d, e). A combination of the reduced longitudinal stress and the reduced effective pressure due to thinning increased the driving stress as the glacier surface steepened. Retreat back into deeper water along the initially reverse-sloping bed allowed the calving rate to increase as a positive feedback. Entry of warm subsurface ocean water enhanced submarine melting and contributed further instability near the grounding line. Fig. 1 andTable 1 suggest that mass loss from the NEGIS has continued at a rate of >10 Gt yr⁻¹ even after a recovery in sea ice concentration and the intrusion of colder subsurface water from the east Greenland current into the fjord systems. This implies continued mass loss and frontal retreat until the NEGIS can reach a new equilibrium force balance (possibly until 25 km upstream from the 2012 calving front location where the bed slope reverses). The most recent predictions of mass loss from Greenland show no or only minor dynamically driven mass loss in the NEGIS basin, the largest in Greenland^44, 45, 46. As recent model projections suggest, ocean warming around Greenland may reach almost double the global mean by 2100⁴⁷ and the recent assessment report of snow, water, ice and permafrost in the Arctic⁴⁸ projects the largest and most pronounced air temperature increase over northeast Greenland⁴⁸, increasing the risk of continued mass loss from this sector of Greenland.

Figure 5: Sea ice concentration along the northeast Greenland coast.

4 comments:

Doug CottonMarch 17, 2014 at 3:00 AM
Whatever's happening with the ice, it's not CO2 causing it.

Neil King from the Skeptical Science team has been unable to fault the physics in my derivation and proof of the existence of the gravito-thermal effect. I presume no one else from the SkS team can do so, even though about 1 in 6 of them have qualifications in physics, including John Cook.

So I think that just about wraps it up as cogent proof, because no one from Judith Curry, Jo Nova, The Air Vent, WUWT, DrRoySpencer, Australian Climate Madness, Clive Best, Bishop Hill, Stoat-Connelly, Open Mind, The Lukewarmer's Way or any other climate blog has been able to prove wrong the answer to the trillion dollar question, namely that the Loschmidt gravito-thermal effect is a reality..

Hence the greenhouse conjecture is debunked once and for all.

Are there any last minute challenges?
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AnonymousMarch 17, 2014 at 5:07 PM
http://stevengoddard.wordpress.com/2014/03/17/new-greenland-paper-demonstrates-again-that-climate-experts-know-nothing-about-climate/
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AnonymousMarch 18, 2014 at 9:59 AM
http://notalotofpeopleknowthat.wordpress.com/2014/03/18/greenland-glaciers-melting-faster/
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MSJune 10, 2014 at 10:29 AM
http://www.sciencedaily.com/releases/2014/06/140609153425.htm
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