Wednesday, December 23, 2015

2015 Arctic Report Card: NOAA Fails Walrus Science!

Good scientists fully understand that complex issues with high uncertainties require two or more working hypotheses. NOAA failed to communicate the great uncertainties and alternatives. Instead NOAA’s report card made claims that hinge on the unproven hypothesis that a reduction in sea ice is detrimental by denying walruses access to foraging habitat. In the Pacific the number of calves per cow increased as has calf survival, both indicators of a growing population, contradicting NOAA’s claim,. As detailed in Hijacking Successful Walrus Conservation, historical records for the Pacific walrus (Fay 1982, 1989) observed an overall increase in the use of land haulouts coinciding with increasing populations of recovering walrus. In the Barents Sea’s Svalbard archipelago, despite the greatest decline of sea ice, recent research has also observed an increased use of land haulouts coinciding with an exponential population growth, a 48% increase in abundance between 2006 and 20012 (Kovacs 2014). Yet despite all the positive indicators, NOAA downplays growing populations and makes the empty assertion, “the overall carrying capacity of the region for walruses is almost certainly declining because of sea ice declines.”

The full weight of evidence suggests an alternative hypothesis is more likely. Less sea ice allows more access to larger areas of bountiful foraging habitat that had been previously covered by heavy ice. The carrying capacity of walrus habitat - its ability to nourish and sustain a population - will only decline if the following are true but perusal of the evidence suggests the carrying capacity has increased.

1) Carrying capacity will decline if the population becomes so abundant it reduces the prey base and
competition for dwindling food creates nutritional stress

2) Carrying capacity will decline if there is a general decline in marine productivity

3) Carrying capacity will decline if the areal extent of potential foraging habitat is reduced, and/or

4) Carrying capacity will decline if access to foraging habitat is reduced.

1. Food Competition, Density-dependent Regulation, and Healthy Vital Rates

Populations are naturally regulated by “density-dependent” factors. As a growing population adds more individuals to a given area, the density increases. As the density approaches the carrying capacity of that habitat, competition for a limited food supply increases nutritional stress. Marine mammals such as polar bears, ringed seals and walruses respond to nutritional stress by reducing their reproductive output, which ultimately reduces population growth. The ratio of calves to cows decreases because pregnancy rates decline, young cows defer their first year of pregnancy to an older age, and calf survival rates decrease. Conversely when the food supply is abundant, walruses’ pregnancy rates increase, cows give birth at an earlier age, and calf survival rates increase. When those critical factors raise the ratio of calves to cows the population increases.

Based on 20th century surveys, researchers believed the Pacific walrus had rebounded from an overhunted population reduced to ~ 50,000 in the 1950s which then grew to ~250,000 to 300,000 walrus by 1980 (Fay 1989). Consistent with density-dependent theory, when the population was below the carrying capacity in the 1950s and 60s, researchers observed the highest ratios of calves per cows. As the population grew subsistence hunters reported increasing numbers of leaner individuals and a steady decline in the ratio of calves to females suggesting walruses were reaching or exceeding the region’s carrying capacity. The resulting decline in reproductive output caused the population growth rate to stop and the population peaked around 1980. Researchers then calculated a brief population decline during 1980s exacerbated by an uptick in Russian walrus harvests (Fay 1997). But the calves:cows ratio then began to increase throughout the 1990s and some researchers believed population growth had resumed. The calves:cows ratio is now as high as it was in the 1960s when the recovering population was rapidly growing (McCracken 2014). Presently calf survival rates have nearly doubled (Taylor 2015) and cow’s age of first pregnancy has been increasingly younger (Garlich-Miller 2006). All those vital signs usually suggest a well fed, growing population, supporting early research but contradicting NOAA’s current argument that the carrying capacity is “certainly declining”.

2. Marine Productivity is Improving

The shallow shelves of the Bering and Chukchi seas prevent nutrients from sinking to a dark abyss far from the reach of photosynthesizing plankton. Shallow seas more readily upwell nutrients enabling high rates of productivity. Furthermore ocean currents bathe large sections of those shallow shelves with nutrient rich subtropical waters further enhancing productivity. And because surface productivity more rapidly reaches the floor of those shallow shelves, bottom dwelling organisms collectively called the “benthos,” receive over 70% of the energy sequestered at the surface. As a result the Bering and Chukchi seas sustain some of the earth’s richest bounty of bottom dwelling prey sought by walrus, gray whales and bearded seals (Sirenko 2007). Contrary to earlier suggestions that global warming may possibly decrease productivity (Grebmeier 2006), satellite observations have determined marine productivity has increased by 30% since the 1990s (Arrigo 2015). The reason for this increase is elementary. Less sea ice allows more photosynthesis. Grebmeier 2015 has now reported that the Bering and Chukchi Sea “hotspots” she has studied have sustained high levels of biomass over the past 4 decades.

From a marine productivity perspective, the evidence does not support NOAA’s claim of a declining carrying capacity; just the opposite. Increased productivity has increased the  carrying capacity.

3. Areal Extent of Foraging Habitat Has Increased

Depth Ppofiles of Bering and Chukchi Seas. Walrus prefer depths less than 60 meters

The key variable that determines walrus foraging habitat is depth. Telemetry studies found walrus spent nearly 98% of their time foraging in shallow water no deeper than 60 meters (Jay 2005) and other observations suggest foraging at depths deeper than 80 meters is unlikely. As seen in Figure 1, much of the Arctic is not suitable for walruses. The darkest blue regions represent inaccessible regions of great depth. The 3 lightest shades of blue-gray outline the only depths with potential walrus foraging habitat.

The white mass in the upper right of Figure 1 represents the summer minimum of the 2007 ice pack. The average historic summer minimum (the yellow line in Fig.1) indicates large portions of the Chukchi Sea’s foraging habitat have been covered with summer ice concentrations of 50% and greater for much of the 20th century. Because walrus avoid ice-covered waters where sea ice concentration is 80% or greater, any heavy ice concentrations reduce the areal extent of walrus foraging habitat.

Notice that along the northern coast of Alaska in the Beaufort Sea, sea ice historically retreated over deep waters every year. Thus the most recent retreat of sea ice further northward did not impact the areal extent of foraging habitat in that region. Likewise once the Chukchi summer sea ice retreated over the deep Arctic Ocean, any additional retreat had little consequence. In contrast, the initial reduction in summer sea ice over the western Chukchi Sea opened vast regions of potential foraging habitat.

It is believed that 70 to 80% of the total Pacific walrus population exploits the western Chukchi habitat especially during the autumn when reduced sea ice exposes the most habitat. Russian researchers surveying the western Chukchi in September of 1980, estimated approximately 150,000 walrus had hauled out in roughly equal numbers on sea ice and on land. A repeat of that survey in October as freezing conditions increased, revealed the number of walrus hauled out on ice had been greatly reduced but walrus on land remained unchanged (Fedoseev 1981). Clearly 75,000 walrus were not forced onto the Russian coast due to the lack of ice. Although the lack of sea ice in 2007 very likely increased the numbers of walrus hauling out on land, media hyperbole that sensationalized terrestrial haulouts are solely due to global warming, inexcusably ignores all historical observations of natural land haulouts. Based on observations that roughly 50% of the walruses use land haulouts despite plentiful potential resting platforms of sea ice, any occupation of land haulouts serves as an indicator of where walrus accessed Chukchi habitat as sea ice cover waxed and waned.

In Figure 3 below (from Garlich-Miller 2011) the numbers locate known land haulouts. The red arrow I added points to Cape Serdse-Kamen (#50) that has always been occupied in September and October during past surveys. The numbers to the west of Cape Serdse-Kamen and to the north around Wrangel Island represent traditional haulouts that are used only in years of light sea ice but unoccupied in years of heavy ice (Fay 1984). For example despite the shallow foraging habitat north of Wrangel Island, walruses were not observed there in the 1980s (Fedoseev 1981). When sub-freezing winds removed much of the thick Arctic ice from this region in the 1990s when Arctic Oscillation shifted, walrus rapidly exploited the region’s resources and over 120,000 walruses hauled around Wrangel Island. Such observations support the hypothesis that reduced ice increases available foraging habitat and consequently the western Arctic’s carrying capacity.

Location of Known Walrus Land Haulouts. From Garlich-Miller 2010

Due to heavy sea ice cover, access to rich foraging habitat on shallow shelves naturally fluctuates between seasons, years, decades and millennia. The heavy ice of the last Ice Age must have been the nadir for walrus populations. Not only was there maximum sea ice coverage, but also the drop in sea level left the shallow shelves of the Arctic Seas high and dry. Although this allowed humans to enter North America, it relegated walrus populations to narrower shelf waters as far south as central California. Eventually Holocene warmth raised sea level and reduced sea ice allowing walrus populations to once again flourish in the Arctic. Flexible migratory patterns are likely an adaptation to the constant changes in sea ice even during the warm Holocene. Proxy data covering the past 9000 years from Point Barrow revealed annual sea ice covering the eastern Chukchi Sea varied from only 5.5 to 9 months, and summer sea surface temperatures ranged from 3 to 7.5 °C, much higher than today (McKay 2008).

Seasonally winter ice forces walrus to abandon the Chukchi. They re-enter after the warmth of spring reduces sea ice cover. Whether caused by CO2-driven global warming, observed natural changes in atmospheric circulation due to the Arctic Oscillation, or changes in the volume of intruding waters associated with the Pacific Decadal Oscillation, the extent of summer sea ice summer has fluctuated greatly over decades as seen in Figure 5 (from Jay 2012.)  

Decadal Changs in Monthly Sea Ice Extent

4. Accessing Foraging Habitat

NOAA began their report card by arguing, “Sea ice deterioration due to global climate change is thought to be the most pervasive threat to ice-associated marine mammals in the Arctic, including walruses.” But that threat has yet to be substantiated. The perceived threat to walruses is solely based on a hypothesis that walruses “require” sea ice as a platform from which they dive to suction clams, worms, etc. from the ocean floor. Based on that belief, some researchers argue that declining sea ice denies access to habitat and forces them to forage closer to their land haulouts. Expanding on that assumption NOAA argues Arctic’s carrying capacity “must be in decline.”

But several lines of evidence clearly demonstrate walruses do not “require” sea ice as a resting platform in order to hunt. A resting platform of sea ice is likely an opportunistic and beneficial convenience - not a requirement. For example after breeding a large proportion of male walruses abandon the sea ice and migrate south to dwell in land haul outs in ice free waters along the Russian and Alaskan coast (represented by red dots in Figure 3). From those traditional land haulouts they embark on foraging trips that last for 4 to 10 days and range as much as 130 kilometers away (Jay 2005). In addition satellite radiotelemetry determined walruses throughout the Bering and Chukchi spend over 80% of their time swimming, and the amount of time in the water was the same whether walrus used sea ice or land for a resting platform. Swimming at a relaxed speed of 10 km/hour, a walrus easily range over 200 km while foraging along the way (Jay 2010, Udevitz 2009).

Some researchers suggest that the lack of resting platforms of sea-ice will restrict walrus to hunting only along the coast and hypothesizing they will more quickly deplete more limited accessible resources. However the opposite scenario is more likely. Heavy sea ice restricts hunting grounds and the most extreme example would occur if heavy ice remained all summer in the Chukchi forcing herds to remain in the Bering Sea throughout the year. Certainly the Bering Sea’s prey base would be rapidly depleted. The migratory behavior of females and their calves into the shallow waters of the Chukchi each summer is most likely a behavior that evolved to reduce resource competition and exploit temporary access to rich foraging habitat.  With a greater reduction of Chukchi summer ice, migrating herds can spread out and reduce localized foraging pressure.

NOAA Expert Opinion Claims Pacific Walrus have declined by 50%. Seriously?

Finally NOAA’s report card suggested that “expert opinion” calculated a 50% decline in Pacific Walrus populations between 1980 and 2000. The experts did agree the population had decreased during the early 1980s due to density-dependent effects when population abundance increased and exceeded the region’s carrying capacity. But the expert consensus ended there. Fay 1986 suggested after a relatively brief decline in the 80s, population growth subsequently resumed. A growing population would be in agreement with recent observations of increased marine productivity, greater access to habitat due to decreased heavy ice, higher calves:cows ratios and higher survival rates.

Estimating walrus abundance is extremely difficult and all experts agree that abundance estimates have extremely wide error bars and are totally unreliable. Russian and American biologists jointly surveyed walrus populations in the autumn every 5 years between 1975 and 1990, but survey efforts were suspended because experts could not agree on how to interpret limited data and the tremendous resulting uncertainty (Speckman 2010). The major problem revolves around estimating how many walrus are in the water and escape detection. Furthermore due walrus movements, it was impossible to replicate survey transects and constrain error estimates. A repeated transect just one week later often resulted in observed numbers differing by 2 or 3 orders of magnitude.

To circumvent survey uncertainties there have been attempts to model abundance based on observed age structure of the population (Taylor 2015), and those model results disagree with earlier calculations of a growing population. They suggested populations continued to decline from 1980 to 2000, but admit their results after 2003 were equivocal. They also acknowledged that information provided by age structure data cannot mitigate uncertainties in the population size, admitting the absolute size of the Pacific walrus population will “continue to be speculative until accurate empirical estimation of the population size becomes feasible

Thus experts would likely agree that NOAA’s claim of a 50% reduction due to “expert opinion” is likewise speculative and rather meaningless. NOAA failed to express that extreme uncertainty and failed to report the tremendous wide range in abundance estimates. For example in the most recent survey (Speckman 2010) of wintering walrus in the Bering Sea, researchers used heat detectors calibrated by high-resolution photographic evidence to estimate abundance. Unfortunately swimming walruses were undetectable. For the region surveyed, they estimated 129,000 walrus that would support a estimated 50% decline. However their 95% confidence ranged from 55,000 to 507,000 walrus. Furthermore due to time and weather constraints, the survey covered less than 50% of the Bering Sea habitat known to contain walrus. A complete survey may well have increased the estimate to well over 200,000 individuals. A midrange estimate would be similar to peak estimates of the 1980s, and high-end estimates would support hypotheses of a growing population in the Pacific; a growth that  parallels observed growth in the Atlantic walrus.

Curiouser and curiouser, NOAA cited McCracken 2014 who used Speckman’s knowingly biased underestimate of 129,000 to suggest the increasing ratio of calves per cow supported a declining walrus population. Biologically such an assertion contradicts density-dependent mechanisms. Increased reproduction increases a population, unless survival rates drastically declined, but rates had increased.

McCracken 2014 Hypothesized Correlation between Calves:Cows ratio and Population Abundance

McCracken 2014 argued that calves:cows ratios are inversely correlated with population abundance as illustrated in Figure 4.  However that correlation is partly speculative and unsupported and depends on using Speckman’s unrealistic estimate of half the population. No one disagrees that overhunting reduced the population in the 1950s so that more food became available for the survivors stimulating walruses to increase reproductive output as evidenced by high calves:cows ratios; a high ratio that approached the theoretical maximum. Density increased as walruses recovered from overhunting (and increasing sea ice was coincidentally recovering from its minimal in the late 1930s) so that the carrying capacity declined and walrus responded with declining calves:cows ratios that bottomed out in the 1980s. But the consensus on any population trends stops in the 1980s.

McCracken 2014 acknowledged that the validity of their inverse correlation is totally dependent upon the assumption that 300,000 walrus was the maximum population that could be sustained by the region. However they did not explore the possibility that the carrying capacity could possibly increase due to less sea ice and higher marine productivity. So they assumed that any observations of higher calves:cows ratios that would normally indicate a growing population, were only possible if the population had declined by such an extent that more food again became available.

The only dynamic that could have possibly offset increased ocean productivity and cause a population decline in an era of regulated hunting, and conservation efforts that are now protecting haulouts, was a strictly hypothetical dynamic that less sea ice prevents access to foraging habitat and was reducing the Arctic’s carrying capacity. But all reported evidence discussed above contradicts that hypothesis and McCracken’s suggestion the population had declined by 50% is untenable.

NOAAs claim that  the “carrying capacity is almost certainly declining because of sea ice declines” is advocated by USGS and US Fish and Wildlife researchers who believe that CO2 warming and declining sea ice must be bad. That belief is advocated in the opening paragraphs of nearly every publication. Wedded to that belief their interpretations ignore robust evidence suggesting less has been beneficial. So one must wonder how politicized those agencies have become and if political pressure has biased their publications. Researchers in those agencies likewise ignored their own observations that it was cycles of thick springtime ice in the Beaufort Sea that caused declines in ringed seals and polar bear body condition. Instead without evidence, they only advocated that reduced summer ice, consistent with CO2 warming, has negatively impacted polar bear populations and walrus Such unsupported biased interpretations are most likely the result of the politicization of science, and I fear this decade will be viewed as the darkest days of environmental science.

Thursday, December 3, 2015

Is Antarctica’s Climate Change Natural or CO2 Driven? There Is Absolutely No Consensus

The record growth of Antarctic sea ice has long been a troubling contradiction for global warming theory. But those who embrace CO2 as the driver of climate change typically countered that global warming was still melting the continental glaciers and raising sea levels. However on October 29, 2015 a team of NASA researchers led by Jay Zwally published the paper “Mass gains of the Antarctic ice sheet exceed losses”. If the new NASA research proves correct - and there is good evidence to suggest it is - continental ice is increasing and lowering sea level. That would highlight another major failure for both CO2 driven models and models of sea level change. The reaction of Dr. Theodore Scambos, senior research scientist at the National Snow & Ice Data Center, was all too reminiscent of the “hide the decline” mentality evidenced by advocacy scientists in the climategate scandal. In an Al Jazeera interview Scambos asked, “Please don’t publicize this study.”  Others pushed back by simply listing any research that disagreed with Zwally, but rarely did they list the research supporting Zwally’s results. Nor did they delve into why there is no Antarctica consensus, as I will do here.

Some researchers did acknowledge the great climate uncertainties. Robin Bell, a research professor at Columbia University's Lamont-Doherty Earth Observatory admitted, "To me this points out that we still don't understand everything about how snow turns into ice and how the ice sheets are changing." Even more revealing were comments posted by Dr. Eric Steig at Michael Mann’s RealClimate website, comments that reveal a total lack of consensus and suggest greater support for natural climate change. Dr Steig has published extensively on Antarctica and has been a regular contributor to the RealClimate website. So he is not someone who can be dismissed as a “denier”.  Steig wrote,

I think the evidence that the current retreat of Antarctic glaciers is owing to anthropogenic global warming is weak. The literature is mixed on this, about 50% of experts agree with me on this.”

On the other side of the issue RealClimate’s Gavin Schmidt downplayed Zwally’s results as we would expect telling interviewers, "I would pin more weight to the GRACE data than to this latest paper." But it is not a matter of putting more weight on satellite data that measures gravity change (GRACE) or satellite data that measures changes in elevation (Zwally et al).  Both methods are victimized by faulty Glacial Isostatic Adjustment models (GIA). All measurements of increased ice elevation or gravity changes are adjusted according to the assumptions of their GIA model of choice. Most GIA models assume Antarctica has been rebounding upwards since deglaciation removed the weight of glacial ice. The degree of estimated rebound depends on the region and more importantly 1) uncertain estimates of the mantle’s viscosity below the bedrock and 2) assumptions about the glacial history of Antarctica.

It is not clear if Schmidt’s advocacy for the GRACE estimates was guided by his persistent protection of the global warming meme, or if his interviewers omitted any honest discussion of papers demonstrating the upward bias in most GIA estimates. Similarly other Zwally detractors pointed to papers such as Harig 2015 that claimed Antarctica was losing ice, but Harig 2015 used GIA models that were well known to over‑estimate glacial rebound.

To remove bias in GIA models, our best method requires comparing Global Positioning System data (GPS) that measures the current bedrock uplift with GIA modeled predictions. This requires placing GPS instruments on solid bedrock, which is relatively rare throughout most of ice covered Antarctica. However along the coast wherever GPS measurements have been possible, research revealed GIA models had biased the  uplift upwards by 4.9 to 5.0 mm/years relative to GPS observations. Zwally argues that current GIA models should be lowered by just 1.6 mm/ year and that small adjustment would bring the estimates based on GRACE data into agreement with Zwally’s elevation data.

There is more evidence to support Zwallys critique of GIA models. In recent years researchers have been lowering their estimates of mass gained during the last Ice Age and lost ice mass during the recent deglaciation. Previous models estimated Antarctica deglaciation contributed 24-37 meters of sea level rise, but  that contribution has now been reduced to just 6-14 meters. This meant early GIA models had grossly overestimated the weight of past glaciers and the subsequent rebound. By adjusting the de‑glaciation history, Whitehouse 2012 revised their GIA model so that the upward bias was reduced to 1.2 mm/year with error estimates of 2.3 mm/year. Less ice also meant previous models that budgeted sources of sea level rise were wrong. Zwally’s estimate that Antarctica has been gaining ice and thus reducing sea level has created more angst that current models of sea level rise are still in need of further adjustments.

Furthermore, Zwally referenced evidence from Siegert 2003 showing parts of east Antarctica had been gaining mass for the past 10,000 years (Figure 2 below). Counter‑intuitively during the last Glacial Maximum ice accumulation dropped to a minimum. In contrast during warmer interglacials greater incursions of moisture entered the interior of Antarctica and ice accumulation peaked. Because east Antarctic is so cold (South Pole’s average summer temperature is -28C), ice ablation is minimal, so it is more likely east Antarctica is still subsiding under that weight, not uplifting. Zwally’s inference that GIA models should decrease their estimates of bedrock uplift by just 1.6 mm/year again is well supported.

Zwally questioned if snow accumulation could continue to offset the ice lost from glacier thinning elsewhere. But recent evidence suggests it will. Zwally’s study did not extended past 2008 but he estimated that during the period studied, net accumulation had reduced sea level rise 0.23 mm/year ( a 6 to 10% reduction). More recent GRACE evidence has suggested even larger accumulation events since then. A 2012 study determined east Antarctica gained 350 Gigatons of snow between 2009 and 2011, enough to decrease sea level rise by 0.32 mm/year. A 2015 study using regional ice core data reveals no unusual temperature changes but an exceptional 30% increase in snow accumulation during the twentieth century, supporting Zwally’s analysis of mass gain in interior west Antarctica.

East Antarctic Ice Accumulation between glacial and interglacial periods

Similarly Greenland’s snowfall accumulation is at all time highs and recent GRACE results show that after several years of accelerated ice loss due to glacier thinning, the net loss from Greenland in 2013-2014 was insignificant. As discussed here, relative to the years of greater ice loss in Greenland, the rate of sea level rise should have dropped by an additional 1.3 mm/year in 2014. Combining Zwally’s calculations with recent evidence from Greenland, sea level models driven by global warming should reveal a decreasing rate of sea level rise. It appears that global warming fears have been misdirecting research concerned with coastal flooding. Research shows groundwater extraction is not only contributing significantly to recent sea level rise, but land is sinking at a faster rate due to that extraction. Regretfully President Obama has highlighted coastal flooding to further politicize climate change, but never mentions the more critical issue of ground water extraction that desperately needs attention.

Zwally’s analysis also noted that previous estimates of Antarctica’s ice mass assumed that increases in elevation were due to snowfall. But when ice accumulation is greater than ice discharge, drainage basins undergo dynamic thickening, and dynamic thickening can occur in response to accumulation events that happened thousands of years ago. Because the density of ice is about 3 times the density of snow, if researchers incorrectly assume increased elevations are only due to snowfall and not dynamic thickening, estimates of ice mass will be greatly underestimated. This points out the need to see climate change within a framework of thousands of years, not just the past few decades, and Zwally’s interpretation of dynamic thickening can be readily tested by additional ice cores.

In the face of Zwally’s analysis, defenders of the CO2 warming meme retreated to stressing uncontested observations of lost ice due to dynamic glacier thinning or uncritically accepting speculative models  catastrophic deglaciation. Although Zwally calculated the net “mass gains from snow accumulation exceeded losses from ice discharge by about 112 and 82 Gt/year respectively during the 1992-2001 and 2003-08 measurement periods”, he also reported that the rate of ice loss along the west Antarctic coast and the peninsula had increased from 64 GT/year to 135 GT/year during those same periods. Alarmists seize upon this short‑term acceleration to suggest rising CO2 will cause the rate of dynamic thinning to increase. But research shows dynamic thinning has been more cyclical, intermittent and episodic with no correlation with CO2 concentrations. For example a large 1987 calving event removed 100 years of ice accumulation from the Ross Ice Shelf in just one day, an amount second only to the loss of the Larsen Ice Shelf. Such episodic events can easily be misinterpreted as an “acceleration” of ice loss. However due to the heavier snow accumulation since that time, the ice shelf has expanded further northward exceeding it previous extent in just over a decade (Keys 1998). Antarctica undergoes rapid ice loss followed by periods of slower recuperation depending on regional rates of snow accumulation. So a much broader timescale of climate change must be embraced.

Research has determined these episodic calving events are most often driven by periodic upwelling of warm Circumpolar Deep Water (CDW) that melts glaciers from below (basal melting). The extremely cold Antarctic climate maintains a 200 to 300 meter  surface layer of near freezing Winter Water that insulates warmer CDW below. All grounding points below 300 meters have been susceptible to basal melting from upwelled CDW for millennia, and a pattern has emerged that glaciers with deeper grounding points incur greater basal melting. Thus the topography of the coastal shelves and depth of submerged glacier grounding points determines the impact of upwelled CDW and limits extreme basal melting to a relatively few locations as illustrated by the red and orange areas in the figure below (from Depoorter 2013)..

Glacial Thinning and Basal Melting Hot Spots

Reports of increased basal melting due to “warmer” water is often misinterpreted to mean CDW water had been warmed by rising CO2. But CDW is a tremendous reservoir of heat that only experiences temperature changes on long‑term scales of centuries and millennia. Upwelled CDW water can be cooled when modified by winter water, or remain warm when it directly accesses a glacier grounding point. Reading recent research carefully reveals no change in the temperature CDW source waters. It is periodic increases in the volume and velocity of intruding CDW that accelerates basal melt. Coastal shelves that allow the  greatest intrusions of relatively warm CDW experience that greatest basal melt such as Pine Island and Thwaites glaciers, which account for the overwhelming majority of Antarctica’s dynamic thinning. Antarctica’s glacial thinning is a very localized phenomenon, and not evidence of global warming.

In addition to conducive topography, intrusions of warm CDW are driven by periodic changes in  the winds which in turn are controlled primarily by the Amundsen Sea Low (ASL), a quasi-permanent low pressure system. The ASL shifts poleward and equatorward, as well as eastward and westward with the seasons. It also shifts in response to inter‑annual and decadal changes in sea surface temperatures in the tropical Pacific. The shifting center of the ASL causes varying wind intensities that also alternate direction between easterlies and westerlies. As illustrated below the direction of the wind over the shelf break determines the amount of CDW that reaches the glaciers grounding points along the peninsula and Amundsen Sea. Paleo‑climate research suggests the position of the ASL also shifts between glacials and interglacials, and drove warm CDW shoreward during interglacials and accelerated glacier retreat.

Modern cycles of CDW‑driven basal melting are likewise correlated with the position of the ASL and changes in the central Pacific temperatures..  Warming of the central Pacific is associated with an El Nino variation called Modoki EL Niño (see Tisdale for further discussion). And here again there is absolutely no consensus regards the effects of CO2 on the frequency or types of El Niño, but most researchers believe El Niño is an expression of the natural climate variability.  Steig 2012 points out that a cycle warming in the central Pacific, similar to recent years, had last occurred during the 1940s. That earlier warming was associated with a large calving event of the Pine Island Glacier that likely occurred in association with an EL Nino event. Accordingly a 2013 paper reports the  “climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics.”

Wind driven upwelling of warm Circumpolar Deep Water (CDW)

Zwally deemed it necessary to acknowledge climate change fears and suggested that if the rate of dynamic thinning continues, Antarctica could begin exhibiting a net loss of ice within the next 20 years, but only if there was no compensating snowfall. Yet curiouser and curiouser neither Zwally or the researchers highlighting accelerated thinning of Amundsen Sea glaciers ever mention recent research that measured a 53% decrease in basal melting and up to a 1C drop in melt water temperatures between 2010 and 2012. Melt water temperatures that were lower under the Pine Island Glacier than 1992 temperatures. The decrease in basal melt was attributed to stronger easterly winds that encouraged downwelling along the Amundsen shelf break, which lowered the top of the thermocline (where cold winter waters meets warm CDW) and reduced the volume of upwelled  warm CDW intruding onto the shelf.  Researchers concluded that “Continuation of a deep thermocline would reverse the current ice-shelf thinning.”

Other researchers have demonstrated warming in Antarctica that followed the last glacial maximum preceded any increase in atmospheric CO2. Both warming and CO2 appear to be driven by changes in the position and strength of the westerly winds and the upwelling of warm CDW. During the past 10,000 years research at Marguerite Bay on the peninsula reveals extensive glacial melt, limited sea ice which enhanced primary productivity that lasted for over 2000 years and was consistent with evidence of increased upwelling of warm CDW. The George VI Ice Shelf collapsed about 9000 years ago but reformed 7000 years ago and that shelf still persists today. Over the last 5000 years intermittent melting and reforming of sea ice in the Marguerite Bay is consistent with enhanced sensitivity to ENSO forcing and increased upwelling of CDW; a similar sensitivity to ENSO events has been documented over the most recent decades. History strongly suggests periods of accelerated glacial thinning are natural and quite common.

A more thorough and objective  review of the peer-reviewed literature reveals an abundance of evidence supporting claims of natural climate variability that easily matches, if not outweighs, the trumpeted papers asserting CO2 driven change. It is no wonder Dr. Steig admitted ““I think the evidence that the current retreat of Antarctic glaciers is owing to anthropogenic global warming is weak. The literature is mixed on this, about 50% of experts agree with me on this.”

It will be of great interest to see how the IPCC spins this state of affairs.