By Kenneth Richard on 23. April 2018
Where’s Anthropogenic Signal?
Since 2000s, An Arctic Warming & Sea Ice Pause …
Cooling In Antarctica … Undermine AGW Claims
It was 3 years ago when scientists first began documenting the pause in Arctic sea ice decline that began in 2007.
While detailing the potential for “cherry-picking” such a short span of years to arrive at “misleading” conclusions, Swart et al. (2015) pointed out that there was a “near-zero” trend in sea ice extent during the brief 2007-2013 period.
“Arctic sea-ice extent was lost at a considerably higher rate from 2001–2007 than in the preceding decades (Fig. 1), which caught the attention of scientists and the public alike. In contrast, from 2007–2013 there was a near-zero trend in observed Arctic September sea-ice extent, in large part due to a strong uptick of the ice-pack in 2013, which has continued into 2014. By deliberately cherry-picking these periods we will demonstrate how using short-term trends can be misleading about longer-term changes, when such trends show either rapid or slow ice loss.”
That “cherry-picked” 6-year pause in Arctic sea ice decline has now been extended another 4 years. As illustrated below, there has been no detectable trend in September Arctic sea ice for the 10 years between 2007-2017.
Image Source (top): NSIDC
While Swart and colleagues correctly assess that “using short-term trends can be misleading about longer-term changes”, they apparently only consider the 1979-2013 Arctic September sea ice trend as “longer-term”. And yet this 34-year period could easily be considered of “cherry-picked” length too because it is also a very short record relative to what is available.
Reconstructions of Arctic (and regional Arctic) sea ice extent reveal that modern values aren’t unusual relative to the longer-term context of the last 100+ years.
12 New Papers Affirm A 21st Century Arctic Warming
Pause As Well As A Rapid Cooling Across Antarctica
1. Since 2005, There Has Been A ‘Warming Hiatus’ In The Arctic
“[W]e find that there was a warming hiatus/slowdown since 2005 at Ny-Ålesund. Additionally, the variation of air temperature lags by 8–9 years, which implies that the warming hiatus probably exists in the Arctic but lags behind, globally. This phenomenon is not an isolated instance, An et al.  reported that the warming rate above 4000 m of the Tibetan Plateau has been slowing since the mid-2000s. In the Antarctic Peninsula, the slowdown of the increasing temperature trend was also found after 1998/1999, however, the reason is attributed to local phenomena, such as the deepening of Amundsen Sea Low and not due to the global hiatus [Turner et al., 2016]. … From the correlation analysis, we found Ny-Ålesund could represent most Arctic areas, especially the Atlantic-Arctic sector. … Especially air temperature, the record of Ny-Ålesund can capture the variation of surface temperature over most of [the] Arctic. … The oscillations of atmospheric dynamic systems, the methods of energy transport from low to high latitudes, and feedback mechanisms of the Arctic on climate change may contribute to the warming hiatus. … [C]limate changes in polar areas remain difficult to predict, which indicates that the underlying mechanisms of polar amplification remain uncertain and debatable.”
2. ‘Marked Cooling’ In Siberia Since 2000
Suvorov and Kitov, 2018 (Eastern Sayan, Siberia)
“The authors examined the variability of activity of modern glaciation and variation of natural conditions of the periglacial zone on climate and on dendrochronological data. Results of larch and Siberian stone pine growth data were revealed at the higher border of forest communities. … It is believed that the temperature could be 3.5 °C warmer at the Holocene optimum than at the present time (Vaganov and Shiyatov 2005). … Since 2000, there has been growth of trees instability associated with a decrease in average monthly summer temperatures. … Since the beginning of 2000, decrease in summer temperatures was marked.”
3. ‘A Cooling Is Observed’ During 2001-2015 In Greenland
“Here we quantify trends in satellite-derived land surface temperatures and modelled air temperatures, validated against observations, across the entire ice-free Greenland. … Warming trends observed from 1986–2016 across the ice-free Greenland is mainly related to warming in the 1990’s. The most recent and detailed trends based on MODIS (2001–2015) shows contrasting trends across Greenland, and if any general trend it is mostly a cooling. The MODIS dataset provides a unique detailed picture of spatiotemporally distributed changes during the last 15 years. … Figure 3 shows that on an annual basis, less than 36% of the ice-free Greenland has experienced a significant trend and, if any, a cooling is observed during the last 15 years (<0.15 °C change per year).”
4. Slight Cooling During 2005-2015 In Greenland
“For the most recent 10 years (2005 to 2015), apart from the anomalously warm year of 2010, mean annual temperatures at the [Greenland] Summit exhibit a slightly decreasing trend in accordance with northern North Atlantic-wide cooling. The Summit temperatures are well correlated with southwest coastal records (Ilulissat, Kangerlussuaq, Nuuk, and Qaqortoq).”
5. A Cooling Observed between 1997-2016 In Arctic Canada
“From 1988 to 1996, the summer intensity of the AO was largely in the positive phase, with a mean value of 0.207 (± 0.135 SE), and this was a period of population stability or growth for each of the three herds that we examined here. In contrast, from 1997 to 2016 the summer AO has remained largely in the negative phase [cooling], with a mean value of − 0.154 (± 0.077 SE), and over this period the Bathurst, Beverly, and Qamanirjuaq herds declined in abundance.”
21st Century Cooling Across Antarctica
6. 2006-’15 Antarctic Peninsula Cooling – A Thinning Ice Sheet Linked To Cooling?
“Active layer monitoring in Antarctica: an overview of results from 2006 to 2015 … Air temperatures showed significant regional differences within the study areas. In the western Antarctic Peninsula region, Vestfold Hills and northern Victoria Land, a slight air temperature cooling was detected, while at other sites in Victoria Land and East Antarctica the air temperature was more irregular, showing no strong overall trend of warming or cooling during the study period (Figure 2). The Antarctic Peninsula region has been reported as the most rapidly warming part of Antarctica (e.g. Turner et al., 2005, 2014), but cooling has been reported since 2000 (Turner et al., 2016). Relatively stable air temperature conditions during the past 20 years were reported in Victoria Land (Guglielmin & Cannone, 2012).”
“Significantly, thicker thaw depths were observed in the colder regions of the eastern Antarctic Peninsula and the coastal zone of East Antarctica. The general pattern suggests that factors other than regional climate should be considered when examining the ground thermal regime (e.g. Hrbáček, 2016). Between 2009 and 2014, substantial active layer thinning was observed at all sites in the western Antarctic Peninsula. The thinning was attributed to climate cooling in the region (Oliva, Navarro, et al., 2017; Turner et al., 2016) and changes in snow cover accumulation, as well as snow persistence during the summer, reducing active layer thaw (de Pablo et al., 2017). In contrast, pronounced active layer thickening between 2010 and 2013 was recorded at Novolazarevskaya in coastal East Antarctica.”
7. The Northern Antarctic Peninsula Cooled By -1.98°C between 2008 and 2014
“As shown by firn core analysis, the near-surface temperature in the northern-most portion of the Antarctic Peninsula shows a decreasing trend (−0.33°C year−1) between 2008 and 2014 [-1.98°C].”
8. Antarctic Peninsula and East Antarctica Cooling Since 1998
Vignon et al., 2018
“The near‐surface Antarctic atmosphere experienced significant changes during the last decades (Steig et al., 2009; Turner et al., 2006). In particular, the near‐surface air over the Western part of Antarctica exhibits one of the major warming over the globe (Bromwich et al., 2013a), with heating rates larger than 0.5 K per decade at some places. Despite a significant warming in the end of the 20th century, the Antarctic Peninsula has been slightly cooling since 1998, reflecting the high natural variability of the climate in this region (Turner et al., 2016). East Antarctica has experienced a slight cooling trend (Nicolas & Bromwich, 2014; Smith & Polvani, 2017) particularly marked during autumn. … General circulation models (GCMs) are very powerful tools for investigating the mechanisms responsible for global or regional changes in the Earth climate. However, we can wonder to what extent they are able to correctly represent the near‐surface temperature field over Antarctica. Although the models involved in the fifth Coupled Models Intercomparison Experiment (CMIP) have a realistic climatology and interannual variability in Antarctica, they fail in reproducing the near‐surface temperature trends in the period 1979–2005 (Smith & Polvani, 2017) and particularly the contrast between west and east Antarctica.”
9. Most Of East Antarctica Has Been Cooling Since 1990s, ‘Significant Cooling’ In Antarctic Peninsula
“The present paper reviews the progress of India’s scientific research in polar meteorology. The analysis of 25 years meteorological data collected at Maitri station for the period 1991–2015 is presented in the paper. The observed trend in the temperature data of 19 Antarctic stations obtained from READER project for the period 1991–2015 has also been examined. The 25 years long term temperature record shows cooling over Maitri station. The Maitri station showed cooling of 0.054 °C per year between 1991 and 2015, with similar pronounced seasonal trends. The nearby Russian station Novolazarevskaya also showed a cooling trend of 0.032 °C per year. … The temperature trend in average temperature of 19 Antarctica stations is also examined to ascertain the extent of cooling or warming trend (Supplementary Table_S1). The majority of stations in East Antarctica close to the coast show cooling or no significant trend. … Turner et al. (2016) using stacked temperature record found a significant cooling trend for the Antarctic Peninsula for the period 1999–2014. Their study suggests that the warming on the Antarctic Peninsula during 1979–1997 and subsequent cooling during 1999–2014 are both within the limits of the decadal time scale natural climate variability of the region. Smith and Polvani (2017) examined the relationship between the SAM and Antarctic surface air temperature trends, in both models and reanalyses. They also found convincing evidence that natural climate variability is the major contributor to the warming of West Antarctica and Antarctic Peninsula. … The Antarctic Sea-ice extent has been showing increasing trend in the recent past few decades. The rate of change in Antarctic sea-ice extent exhibit strong regional differences with increase in some regions and decrease in other. The mean Antarctic sea-ice extent increased at a rate of 1.2–1.8% per decade between 1979 and 2012 (IPCC, 2013). Gagné et al. (2015) attributed increase in Antarctic sea-ice extent to internal variability.”
10. Models Fail To Simulate The Southern Ocean Cooling And Circumpolar Increase In Sea Ice
“Observed Southern Ocean changes over recent decades include a surface freshening (Durack and Wijffels 2010; Durack et al. 2012; de Lavergne et al. 2014), surface cooling (Fan et al. 2014; Marshall et al. 2014; Armour et al. 2016; Purich et al. 2016a) and circumpolar increase in Antarctic sea ice (Cavalieri and Parkinson 2008; Comiso and Nishio 2008; Parkinson and Cavalieri 2012). … [A]s high-latitude surface freshening is associated with surface cooling and a sea ice increase, this may be another factor contributing to the CMIP5 models excessive Southern Ocean surface warming contrasting the observed surface cooling (Marshall et al. 2014; Purich et al. 2016a), and sea ice decline contrasting the observed increases (Mahlstein et al. 2013; Polvani and Smith 2013; Swart and Fyfe 2013; Turner et al. 2013; Zunz et al. 2013; Gagne et al. 2015) over recent decades. … Our results suggest that recent multi-decadal trends in large-scale surface salinity over the Southern Ocean have played a role in the observed surface cooling seen in this region. … The majority of CMIP5 models do not simulate a surface cooling and increase in sea ice (Fig. 8b), as seen in observations.”
11. Temperature (Non) Trend Across Antarctica (90°S To 60°S)
“The study of Antarctic precipitation has attracted a lot of attention recently. The reliability of climate models in simulating Antarctic precipitation, however, is still debatable. This work assess the precipitation and surface air temperature (SAT) of Antarctica (90°S to 60°S) using 49 Coupled Model Intercomparison Project phase 5 (CMIP5) global climate models”
12. ‘Ubiquitous’ Cooling Across East Antarctica Since The 1970s
“Over the past 60 years, the climate of East Antarctica cooled while portions of West Antarctica were among the most rapidly warming regions on the planet. The East Antarctic cooling is attributed to a positive trend in the Southern Annular Mode (SAM) and a strengthening of the westerlies, while West Antarctic warming is tied to zonally asymmetric circulation changes forced by the tropics. This study finds recent (post-1979) surface cooling of East Antarctica during austral autumn to also be tied to tropical forcing, namely, an increase in La Niña events. … The South Atlantic anticyclone is associated with cold air advection, weakened northerlies, and increased sea ice concentrations across the western East Antarctic coast, which has increased the rate of cooling at Novolazarevskaya and Syowa stations after 1979. This enhanced cooling over western East Antarctica is tied more broadly to a zonally asymmetric temperature trend pattern across East Antarctica during autumn that is consistent with a tropically forced Rossby wave rather than a SAM pattern; the positive SAM pattern is associated with ubiquitous cooling across East Antarctica.
April 23, 2018 at 08:14AM
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