Antarctica Has Not Warmed In Over A Century
Natural Variability – Not Humans – Drives Ice Melt
The most recent mass media contribution to the canon of climate alarmism referenced a study claiming that "climate change" (i.e., human-caused deep ocean warming) was responsible for the Amundsen Sea's (West Antarctica) "rapid melting" of the Thwaites Glacier.
Image Source: New York Times
A few months ago, however, scientists (Jenkins et al., 2018) reported that the Amundsen Sea sector – where Thwaites glacier is located – has been in a cooling phase since 2009-'11.
Furthermore, the ocean in this region warms and cools in accordance with decadal-scale cycles. Consequently, the authors conclude that the "accelerated mass loss from the Amundsen Sea sector of the [West Antarctic Ice Sheet, WAIS] has not resulted from progressive ocean warming or unstable ice retreat."
This would appear to contradict the claim that rapidly and linearly rising anthropogenic CO2 emissions are what lies behind the ocean warming and/or ice sheet melt for this region.
Image Source: Jenkins et al., 2018
Antarctic ice melt, temperature, sea ice…driven by natural variability
It is well documented in the scientific literature that climatic trends in and around Antarctica are predominantly controlled by natural mechanisms and internal variability, not greenhouse gas emissions.
A newly published paper (Scott, 2019), for example, identifies the forcing mechanisms behind the ice melt in the Amundsen Sea region of the WAIS during 1979-2017. Neither anthropogenic influences or greenhouse gas concentrations are mentioned anywhere in the paper as factors in Antarctic ice melt trends.
"Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multidecadal reanalysis and satellite datasets. Physical drivers of ice melt are diagnosed by comparing satellite-observed melt patterns to anomalies of reanalysis near-surface air temperature, winds, and satellite-derived cloud cover, radiative fluxes, and sea ice concentration based on an Antarctic summer synoptic climatology spanning 1979–2017. Summer warming in West Antarctica is favored by Amundsen Sea (AS) blocking activity and a negative phase of the southern annular mode (SAM), which both correlate with El Niño conditions in the tropical Pacific Ocean. Extensive melt events on the Ross–Amundsen sector of the West Antarctic Ice Sheet (WAIS) are linked to persistent, intense AS blocking anticyclones, which force intrusions of marine air over the ice sheet. Surface melting is primarily driven by enhanced downwelling longwave radiation from clouds and a warm, moist atmosphere and by turbulent mixing of sensible heat to the surface by föhn winds. Since the late 1990s, concurrent with ocean-driven WAIS mass loss, summer surface melt occurrence has increased from the Amundsen Sea Embayment to the eastern Ross Ice Shelf. We link this change to increasing anticyclonic advection of marine air into West Antarctica, amplified by increasing air–sea fluxes associated with declining sea ice concentration in the coastal Ross–Amundsen Seas." (Scott, 2019)
In a comprehensive analysis of the surface climate in and around Antarctica during 1979-2014 – including the cooling Southern Ocean – 25 scientists (Jones et al., 2016) assert that climate models predicated on anthropogenic forcing "are not compatible with the observed trends", and that "natural variability overwhelms the forced [anthropogenic] response in the observations".
Image Source: Jones et al., 2016
Scientists: Antarctica hasn't warmed in over a century
Recent climate trends for the West Antarctic Ice Sheet have not offset the long-term cooling trend. The region was actually much warmer than modern for most of the last 2000 years.
Image Source: Stenni et al., 2017
In fact, recent paleoclimate evidence suggests (Stenni et al., 2017) that "no continent scale warming of Antarctica is evident in the last century."
Image Source: Stenni et al., 2017
The Antarctic Peninsula warmed rapidly, but the rest of the continent cooled over the last century
An earlier (2008) continent-wide climate data compilation revealed that although models of anthropogenic forcing simulated a climate warming of +0.75°C, Antarctica as a whole warmed by "only 0.2°C" over the last century.
Most of the continent has cooled since the early 1900s.
The Antarctic Peninsula, which warmed by "several degrees", drove the net continental temperature trend into positive territory, compensating for the cooling throughout East Antarctica.
Image Source: Newton, 2008
The Antarctic Peninsula has rapidly (-0.47°C per decade) cooled since the late 1990s
As mentioned, the Antarctic Peninsula was the only anomalously warming sector of an otherwise-cooling Antarctic continent over the last several decades to century. It warmed by a rapid +0.32°C per decade from 1979-1997.
Then, beginning in about 1998-'99, the Peninsula began cooling even more rapidly than it had been warming. By 2014, all of the warming since 1979 had been offset, revealing an overall non-warming trend (Turner et al., 2016).
Image Source: Turner et al., 2016
The northern-most portion of the Antarctic Peninsula cooled by -1.98°C between 2008-2014.
Image Source: Fernandoy et al., 2018
The Larsen Ice Shelf station has been cooling at a rate of -1.8°C per decade since 1995.
Image Source: Mörner et al., 2018
Surface mass balance gains for Antarctic Peninsula glaciers since 2009
"Two small glaciers on James Ross Island, the north-eastern Antarctic Peninsula, experienced surface mass gain between 2009 and 2015 as revealed by field measurements. A positive cumulative surface mass balance of 0.57 ± 0.67 and 0.11 ± 0.37 m w.e. was observed during the 2009–2015 period on Whisky Glacier and Davies Dome, respectively. … Ambrožová and Láska (2016) reported a significant decrease (0.03–0.15°C a−1 [-0.3 to -1.5°C per decade]) in the temperature along the AP [Antarctic Peninsula] over the 2005–15 period with the most prominent cooling at the Bibby Hill station on JRI [James Ross Island]. … The cumulative mass gain of the glaciers around the northern AP [Antarctic Peninsula] indicates a regional change from a predominantly negative surface mass balance in the first decade of the 21st century to a positive balance over the 2009–15 period. The change in the glacier mass balance follows a significant decrease in the warming rates reported from the northern AP [Antarctic Peninsula] since the end of the 20th century. The mass gain is also consistent with the regional trend of climate cooling on the eastern side of the AP [Antarctic Peninsula]." (Engel et al., 2018)
Image Source: Engel et al., 2018
Eastern and southern Antarctica have also been cooling during the last decade(s)
Image Source: Herbacek et al., 2018
Image Source: Ramesh and Soni, 2018
The overall non-warming/cooling trend for Antarctica may extend back to the 1960s and 1970s
Image Source: Goursaud et al., 2018
Image Source: Doran et al., 2002
An alternative mechanism underlying the Thwaite Glacier's recent retreat
It is widely accepted that geothermal heat flux (volcanic activity) beneath the West Antarctic ice sheet – and Thwaites Glacier – is a "critical factor" in the active melting for the region.
Image Source: Schroeder et al., 2014
Image Source: Dziadek et al., 2019
An attribution reassessment is needed
Considering widespread modeling failures with trend simulation for Antarctica, perhaps there should be a reassessment of the factors and mechanisms underpinning the continent's variable climate and ice sheet melt.
The assumption that humans are driving the changes in Antarctica is not compatible with observations.
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