Recent Antarctic ‘Meltdown’ Is Natural Variability

The accelerated warming in West Antarctica (WA) and the Antarctic Peninsula (AP) is due to a natural mode of climate change according to a very recently released paper in AAAS. It’s been known for some time that the pronounced warming in WA compared to East Antarctica (EA) was very likely due to a mode of […]

Recent Antarctic ‘Meltdown’ Is Natural Variability — Iowa Climate Science Education

The accelerated warming in West Antarctica (WA) and the Antarctic Peninsula (AP) is due to a natural mode of climate change according to a very recently released paper in AAAS. It’s been known for some time that the pronounced warming in WA compared to East Antarctica (EA) was very likely due to a mode of natural variability and I’ve highlighted this myself on this blog on numerous occasions in comments and on posts. However, as global warming dogma is largely immune to facts and data which do not support the ‘reality’ of climate change, the myth has persisted that the Antarctic is melting down dangerously because of climate change and we’re all going to drown from catastrophic sea level rise as a result.

I was alerted to the paper by the GWPF:

West Antarctica has always been looked on by alarmists as being the southern example of polar temperature amplification – a phenomenon predicted by most climate change models. The Arctic temperature amplification is very apparent so there must be an Antarctic equivalent, and there it is.

But while scientists have been well aware that Antarctica is warming asymmetrically, with West Antarctica experiencing more than East Antarctica and frequently attributed to climate change, the underlying causes of this phenomenon have been poorly understood, and the suggestion that West Antarctica may be experiencing natural warming has been suggested before though not taken up very enthusiastically, if at all.

Poor understanding in climate science is usually the cue to attribute any unexplained phenomenon to demon CO2. That’s how it works. Climatologists in the pay of Big Green can’t explain something apparently extraordinary about the natural world, so therefore it must be climate change. But that is now not the case with warming in WA if this latest paper is taken in conjunction with many other studies suggesting a dominant natural mode of variability is responsible for recent pronounced warming in Antarctica.

This new paper, “The internal origin of the west-east asymmetry of Antarctic climate change”, expresses the dilemma well. In explaining the asymmetry, it suggests factors such as atmosphere-ocean feedbacks along the coast of West Antarctica and the shape of the Antarctic terrain combine to create a pattern of upper troposphere circulation over the West Antarctic subcontinent that flows opposite to the Earth’s rotation.

The GWPF also point out that the release of the paper is being sidelined by the media because its conclusions don’t fit the global warming narrative, which is no doubt true:

The embargoed information from Science journal is normally released four days before the embargo is lifted on Thursday evening UK time. Thousands of journalists around the world see it as Science along with Nature are the world’s leading science journals. So why is it that no mainstream news media covered this important story? It’s not as though there were any other pressing environment stories to eclipse it.

What it demonstrates is the asymmetry in environment and science reporting. If the story confirms the dire news that anthropogenic climate change affects everything and is visible anywhere it’s much more likely to be trumpeted by the mainstream media than if it explains some of the climatic changes we see is due to mother nature.

So anyway, I thought I would give the paper a closer look and it actually gets even more interesting once you start to read it. This is what the Abstract says:

Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although this asymmetric feature is well recognized, its origin remains poorly understood. Here, by analyzing observation data and multimodel results, we show that a west-east asymmetric internal mode amplified in austral winter originates from the harmony of the atmosphere-ocean coupled feedback off West Antarctica and the Antarctic terrain. The warmer ocean temperature over the West Antarctic sector has positive feedback, with an anomalous upper-tropospheric anticyclonic circulation response centered over West Antarctica, in which the strength of the feedback is controlled by the Antarctic topographic layout and the annual cycle. The current west-east asymmetry of Antarctic surface climate change is undoubtedly of natural origin because no external factors (e.g., orbital or anthropogenic factors) contribute to the asymmetric mode.

The authors examine reconstructed surface air temperature over the Antarctic continent from 1958-2012. The identify a clear asymmetric pattern of warming, with most of it occurring over WA. They analyse the data thus to identify two modes of Antarctic climate variability:

Thus, we apply the empirical orthogonal function (EOF) analysis to annual-mean SATs over Antarctica, which yields the first EOF mode (EOF1) representing single-signed variability over the entire continent (Fig. 1B) and the second EOF mode (EOF2) representing a seesaw pattern with its node along the Transantarctic Mountains

EOF2 is the natural multidecadal mode of climate variability which has been responsible for accelerated warming in WA, where the Thwaites and Pine Island glaciers are located, which have both receded considerably, leading to many scare stories in the media about global warming melting Antarctic ice sheets and causing sea level to rise.

In the concurrent positive phase of the two modes, West Antarctica experiences substantial warming by the reinforcement of the two modes, while over East Antarctica, opposite-signed variabilities in the two modes lead to weak warming.

The authors identify the peculiar topography of the Antarctic continent as being the main factor behind the EOF2 mode of climatic variability:

The fact that the second mode consistently shows no relationship with external global-scale forcing changes in the diverse datasets suggests that this variability could be manifested by climate factors in the Antarctic and adjacent regions. The Antarctic topographical distinction between the WAIS and EAIS, divided by the TAM, could be a major factor because it differentiates any influence on Antarctica between the two ice sheets. Thus, we perform sensitivity experiments on changing Antarctic terrains using a coupled atmosphere-ocean model to demonstrate whether the topographical distinction is a key factor behind the asymmetric climate mode. With the current Antarctic terrain, the coupled atmosphere-ocean model produces an asymmetric mode similar to that observed in terms of the spatial pattern (Fig. 5A). The experiment with the flattened EAIS shows that the asymmetric mode becomes stronger with the expansion of the West Antarctic warm region farther toward East Antarctica (Fig. 5B). In contrast, the elevated WAIS experiment produces a weak asymmetry with the negligible West Antarctic warming (Fig. 5C).

After explaining in detail the possible meteorological mechanisms behind the accelerated warming in WA, the authors identify internally generated multidecadal variability as the probable driving force:

. . . . . . the enhanced asymmetric trend between West and East Antarctica during recent decades could be a manifestation of multidecadal variability.

But what about the other mode of Antarctic climate variability, EOF1? For this, we need to wheel in the all-singing, all-dancing, multimillion pound mainframe number-crunching, amazing technicolour climate models! CMIP5 to be exact:

Modern instrumental records over Antarctica are too short to illustrate the potential multidecadal natural variability in these climate modes. Furthermore, the single observational representation limits our confidence in elucidating the nature of the variability. Therefore, climate model simulations are valuable for complementing observational deficiencies over Antarctica. Thus, we examine the widely used multimodel data from the Coupled Model Intercomparison Project phase 5 (CMIP5)

They identify two modes:

Most CMIP5 models simulate two observed modes with amplitudes of more than 0.8

So far, so good. But, long faces, they don’t simulate the observed data re. the second, multidecadal variability mode very well at all. Isn’t that unusual? Climate models fail to simulate natural variability! Oh dear, what a shame, never mind, we can always throw more taxpayers’ money at them and the mainframes which they run on to make them more realistic and thus prove that natural climate change is no big deal compared to anthropogenic climate change, which gifted far-sighted intuitive genius climate scientists have been telling us for years anyway. I’m sure CMIP6 will make a big difference . . . . .

However, the second mode shows a weak negative trend in multimodel mean values in contrast to the increasing trend in the observations. Discrepancies in the second mode might be one of the reasons why the CMIP5 models could not capture recent Antarctic asymmetric trends

All is not lost however. It turns out that the first mode of climatic variability (EOF1) is linked to global warming, which is quite amazing considering that climate models are not biased at all to find the fingerprint of man-made global warming in temperature data.

The first mode robustly shows an increasing trend in the CMIP5 models, as it does in the observations (see the red circles in Fig. 2C). The strengthening of the first mode under global warming in NB2014 and the CMIP5 historical simulations suggests that this mode might be closely linked to a global temperature rise. This can also be inferred from the substantial across-model correlation between the simulated global mean temperature trend and the amplitude of the first mode in the CMIP5 models (r = 0.61).

The authors then go on to investigate the two climatic modes of variability using longer proxy datasets and NCAR’s Community Earth System Model (CESM1):

To find robust evidence for the characteristics of the two modes in the longer period, we further analyze multiple datasets of long-term Antarctic surface temperatures, including proxy-based reconstruction data and climate modeling results: surface temperature reconstruction for the last 2000 years (PAGES Antarctica2k) (34), two long-term modeling results from the mid-Holocene [LOVECLIM and TraCE-21K (35)], and four simulations for the 20th and 21st centuries by CESM1

Now here’s where it gets interesting, because LOVECLIM and indeed all the datasets reveal a consistent cooling trend since the mid-Holocene. But PAGES 2k Antarctica reveals an abrupt hockey-stick warming beginning about 1900, as does (of course) CESM1, accelerating (of course) into the 21st century.

In addition, the first PCs from all datasets reflect the long-term variation in radiatively forced global-scale climate change: a gradual cooling from the mid-Holocene to the present (LOVECLIM); an abrupt warming after a long-term cooling trend, shaped similarly to a hockey stick, during the last two millennia (PAGES Antarctica2k); and a sustained warming in the historical and future simulations under greenhouse gas (GHG) influences by CESM1-CAM5

Note PAGES2k shows an even stronger cooling of Antarctica over the last two thousand years than even LOVECLIM.

There’s RCP8.5 again also, melting down the Antarctic ice sheets and drowning us all in the process. You know it’s going to happen. Greta says so. Million year old meltwater is going to make life hell by 2100 unless we start living like carbon neutral eco-peasants right now.

The authors make it plain:

he climatic modes in this study suggest an important implication for future climate change in East Antarctica under global warming. The two future climate change experiments suggest that the explained variance in the first mode is much higher in the 21st century, while the second mode diminishes. The characteristics of the two modes strongly suggest that if global warming continues, a substantial temperature increase over East Antarctica may occur in addition to ongoing West Antarctic warming. The asymmetric mode will persist at its own pace in the future, even under global warming, but its role may not be as great as it is now. The intensified global warming over all of Antarctica in the future can induce massive melting of the ice shelves, even in East Antarctica. This explains why we have to keep an eye on Antarctica as global warming continues, despite the recent mitigation of warming in the eastern part of the region, due to the asymmetric nature of climate change.

OMG, we’ve been lucky so far because natural variability, which has been the main cause of scary glacial melting in WA (wrongly attributed to AGW) is going to take a break in the 21st century and global warming is going to accelerate massive melting of the huge ice sheets in EA!

The ‘evidence’ for this is the modelled first mode of Antarctic climate variability (EOF1), linked to man-made global warming, the PAGES2k hockeystick reconstruction and the historical and future projections of climate change simulated by CESM1 under RCP4.5 and RCP8.5, no doubt with the empahsis firmly on RCP8.5.

There’s a fly in the ointment though – well, several actually, but the biggest is PAGES2k. According to Steve McIntyre, this is what PAGES2k Antarctica looked like in 2013. Spot the hockey stick? No, me neither.

As Steve explains:

Here is a plot of the PAGES2K Antarctic temperature reconstruction. It showed a long decline from mid-first millennium, with nearly all 19th and 20th century values and even early 21st century below the long-term mean.

This series was used in IPCC AR4 (see below). Though its most recent portion is rather muddy in the IPCC diagram, the lack of any 20th century blade is clear.

It all changed in 2017 when Stenni et al produced a revised Antarctic long term PAGES record which included some decidedly very dodgy borehole records, criticised in detail by McIntyre at Climate Audit. Guess what? Our current paper on Antarctic climatic variability uses Stenni et al PAGES2k, 2017. That’s why they get the hockey stick abrupt warming, which was not evident in the 2013 data.

Conclusion: recent (1958-2012) Antarctic warming in the West and the Peninsula is almost certainly due to a natural multidecadal mode of variability. The only evidence that continent wide Antarctic warming will become a menace to the world in the 21st century is climate models and a very dodgy revised PAGES2k dataset which conjured up a hockey stick where none existed previously.

via Climate Scepticism

June 18, 2020 at 06:10PM