Anthropogenic Influence On Arctic Climate
‘Too Small To Be Detected’
Source: Haine, 2016
The evidence compiled in scientific papers continues to rapidly accumulate.
An anthropogenic signal in the regional Arctic climate is still too small to be detected.
Temperature, glacier melt, and sea ice changes are all well within the range of natural variation for the Arctic region. The changes that do occur have identifiable origins that are unrelated to atmospheric CO2 concentrations or human emissions.
Below is a brief summary of some of the latest research that underscores the lack of connection between anthropogenic influences and climate-related changes in the Arctic.
Arctic Temperature And Ice Retreat Mechanisms
1. Arctic Warming Since 1990s ‘Dominated By Natural Variability’ (NAO)
Orsi et al., 2017
The recent warming trend in North Greenland … We find that δ 18O [temperature/climate proxy] has been increasing over the past 30 years, and that the decade 1996-2005 is the second highest decade in the 287-year record (Figure 4). The highest δ 18O values were found in 1928, which is also an extreme year in GISP2 and NGRIP ice cores, and in a coastal South Greenland composite [Vinther et al., 2006; Masson-Delmotte et al., 2015], but the decadal average (1926-1935) is not statistically different from the decade (2002-2011).
The surface warming trend has been principally attributed to sea ice retreat and associated heat fluxes from the ocean [Serreze et al., 2009; Screen and Simmonds, 2010a, b], to a negative trend in the North Atlantic Oscillation (NAO) since 1990, increasing warm air advection on the West Coast of Greenland and Eastern Canada [Hanna et al., 2012; Fettweis et al., 2013; Ding et al., 2014], and to an increase in the Greenland Blocking Index [Hanna et al., 2013]. These latter mechanisms could be dominated by natural variability rather than forced response to the anthropogenic increase in greenhouse gases [Fettweis et al., 2013; Screen et al., 2014].
2. Arctic Ice Melt Since 1995 Due To Natural Cloud Cover Decrease, NAO
Hofer et al., 2017
Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet … The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. … We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud coverenhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation. … Th[e] strong correlation between summertime NAO index and the MAR-based cloud cover could be used to forecast whether the observed reduction in cloud cover during summer, and the associated increase in GrIS melt, is likely to continue.
3. Geothermal Heat Flux From ‘All Over’ Greenland The ‘Primary Process’ Behind Temperature Changes
Rysgaard et al., 2018
The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers. … Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth’s interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature and salinity time series (2005–2015) in the deep stagnant basin water are used to quantify a GHF of 93 ± 21 mW m−2 which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream. … Geothermal springs with source water temperatures above 0 °C have been found all over Greenland, especially around Disko Island in West Greenland, where several thousands of such springs have been identified. … Therefore, we assume that vertical turbulent mixing andGHF [geothermal heat flux] are the primary processes behind the observed salinity and temperature change.
4. Recent Winter Arctic Warming Driven By Planetary Scale Waves
Baggett and Lee, 2017
The dynamical mechanisms that lead to wintertime Arctic warming during the planetary-scale wave (PSW) and synoptic-scale wave (SSW) life cycles are identified by performing a composite analysis of ERA-Interim reanalysis data. The PSW life cycle is preceded by localized tropical convection over the Western Pacific. Upon reaching the mid-latitudes, the PSWs amplify as they undergo baroclinic conversion and constructively interfere with the climatological stationary waves. The PSWs [planetary scale waves] flux large quantities of sensible and latent heat into the Arctic which produces a regionally enhanced greenhouse effect that increases downward IR and warms the Arctic two-meter temperature. The SSW life cycle is also capable of increasing downward IR and warming the Arctic two-meter temperature, but the greatest warming is accomplished in the subset of SSW events with the most amplified PSWs. Consequently, during both the PSW and SSW life cycles, wintertime Arctic warming arises from the amplification of the PSWs [planetary scale waves].
5. Recent Canadian Arctic Warming (1988-1996) And Cooling (1997-2016) Driven By The AO
Mallory et al., 2018
The AO [Arctic Oscillation] has positive and negative phases that infuence broad weather patterns across the northern hemisphere (Thompson et al. 2000). For example, during the positive phase of the AO, atmospheric pressure over the Arctic is lower than average, which tends to result in warmer and wetter winters in northern regions as warmer air is able to move further north (Thompson et al. 2000; Aanes et al. 2002). … 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. … We found that positive intensities of the Arctic Oscillation (AO) in the summer were associated with warmer temperatures, improved growing conditions for vegetation, and better body condition of caribou.
6. Greenland Glacier Retreat, Growth Linked To The NAO
Bjørk et al., 2017
Changes in Greenland’s peripheral glaciers linked to the North Atlantic Oscillation … [W]e map glacier length fluctuations of approximately 350 peripheral glaciers and ice caps in East and West Greenland since 1890. Peripheral glaciers are found to have recently undergone a widespread and significant retreat at rates of 12.2 m per year and 16.6 m per year in East and West Greenland, respectively; these changes are exceeded in severity only by the early twentieth century post-Little-Ice-Age retreat. Regional changes in ice volume, as reflected by glacier length, are further shown to be related to changes in precipitation associated with the North Atlantic Oscillation (NAO), with a distinct east–west asymmetry; positive phases of the NAO increase accumulation, and thereby glacier growth, in the eastern periphery, whereas opposite effects are observed in the western periphery. Thus, with projected trends towards positive NAO in the future, eastern peripheral glaciers may remain relatively stable, while western peripheral glaciers will continue to diminish.
7. Arctic’s Polar Vortex Changes ‘Primarily A Result Of Natural Internally-Generated Climate Variability’
Weakening and shift of the Arctic stratospheric polar vortex: Internal variability or forced response? … By comparing large ensembles of historical simulations with pre-industrial control simulations for two coupled climate models, the ensemble mean response of the vortex is found to be small relative to internal variability. There is also no relationship between sea-ice decline and trends in either vortex location or strength. Despite this, individual ensemble members are found to have vortex trends similar to those observed, indicating that these trends may be primarily a result of natural internally-generated climate variability.
Arctic Temperature Changes In Recent Decades
8. No Net Warming Since 1940s/1950s In Alaska, Subarctic North Atlantic, Siberia…Climate Trends Consistent With 50-90 Year AMO
Nicolle et al., 2018
Persistent multidecadal variability with a period of 50– 90 years is consistent between the subarctic North Atlantic mean record and the AMO over the last 2 centuries (AD 1856–2000). … In the North Atlantic sector, instrumental sea surface temperature (SST) variations since AD 1860 highlight low-frequency oscillations known as the AMO (Kerr, 2000). … The LIA is, however, characterized by an important spatial and temporal variability, particularly visible on a more regional scale (e.g., PAGES 2k Consortium, 2013). It has been attributed to a combination of natural external forcings (solar activity and large volcanic eruptions) and internal sea ice and ocean feedback, which fostered long-standing effects of short-lived volcanic events (Miller et al., 2012).
9. Greenland Has Been Cooling Since 2001
Westergaard-Nielsen et al., 2018
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).
10. Greenland Has Been Cooling Since 2005
Kobashi et al., 2017
For the most recent 10 years (2005 to 2015), apart from the anomalously warm year of 2010, mean annual temperatures at the 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).
11. No Net Warming In Greenland For The Last 90 Years
Kobashi et al., 2017
Arctic Sea Ice Changes
12. Arctic Sea Ice Expanding Since 1988 (Bohai Sea), AO & NAO ‘Primary’ Climate Factors
Yan et al., 2017
Afforded by continuous satellite imagery, evolution of sea ice cover over nearly three decades from 1988 to 2015 in the Bohai Sea [North China] as a peculiar mid-latitude frozen sea area is reported for the first time. An anomalous trend of slight overall increase of 1.38 ± 1.00% yr–1 (R = 1.38, i.e. at a statistical significance of 80%) in Bohai Sea ice extent was observed over the 28 year period. … Correlation with decreasing Arctic Oscillation (AO) index (r = –0.60, p < 0.01) and North Atlantic Oscillation (NAO) index (r = –0.69, p < 0.01) over the study period suggested AO and NAO as the primary large-scale climate factors for Bohai Sea ice.
13. Arctic Sea Ice Oscillates…Not Significantly Lower Now Than In The 1940s
Connolly et al., 2017
According to this new dataset, the recent period of Arctic sea ice retreat since the 1970s followed a period of sea ice growth after the mid 1940s, which in turn followed a period of sea ice retreat after the 1910s. Our reconstructions agree with previous studies that have noted a general decrease in Arctic sea ice extent (for all four seasons) since the start of the satellite era (1979). However, the timing of the start of the satellite era is unfortunate in that it coincided with the end of several decades during which Arctic sea ice extent was generally increasing. This late-1970s reversal in sea ice trends was not captured by the hindcasts of the recent CMIP5 climate models used for the latest IPCC reports, which suggests that current climate models are still quite poor at modelling past sea ice trends.
14. Arctic Sea Ice Extent Only Slightly Lower Now Than During Little Ice Age, Much Higher Now Than Most Of Last 7,000 Years
Perner et al., 2018
[W]e find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the ‘2800 years BP cooling event’, the ‘Dark Ages’ and the ‘Little Ice Age’, whereas the ‘Roman Warm Period’ and the ‘Medieval Climate Anomaly’ parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late Holocene, suggesting ENSO as a potential mediator.
15. Solar Forcing Drives Arctic Sea Ice Trends, Sea Ice Higher Now Than Nearly All Of The Last 8,000 Years
Yamamoto et al., 2017
Millennial to multi-centennial variability in the quartz / feldspar ratio (the BG [Beaufort Gyre] circulation) is consistent with fluctuations in solar irradiance, suggesting that solar activity affected the BG [Beaufort Gyre] strength on these timescales. … Multi-century to millennial fluctuations, presumably controlled by solar activity, were also identified in a proxy-based BSI [Bering Strait in-flow] record characterized by the highest age resolution. … Proxy records consistent with solar forcing were reported from a number of paleoclimatic archives, such as Chinese stalagmites (Hu et al., 2008), Yukon lake sediments (Anderson et al., 2005), and ice cores (Fisher et al., 2008), as well as marine sediments in the northwestern Pacific (Sagawa et al., 2014) and the Chukchi Sea (Stein et al., 2017).
16. Southwest Greenland: Sea Ice Increasing Since 1930s, No Net Change In Temperature Since 1600
Kryk et al., 2017
Our study aims to investigate the oceanographic changes in SW Greenland over the past four centuries (1600-2010) based on high-resolution diatom record using both, qualitative and quantitative methods. July SST during last 400 years varied only slightly from a minimum of 2.9 to a maximum of 4.7 °C and total average of 4°C. 4°C is a typical surface water temperature in SW Greenland during summer.
The average April SIC [sea ice concentration] was low (c. 13%) [during the 20th century], however a strong peak of 56.5% was recorded at 1965. This peak was accompanied by a clear drop in salinity (33.2 PSU).
17. Arctic Sea Ice Trends Linked To The AMO, NAO, Sea Ice Lower Than Today During Medieval Climate Anomaly
Kolling et al., 2017
[O]ur reconstructions reveal several oscillations with increasing/decreasing sea ice concentrations that are linked to the known late Holocene climate cold/warm phases, i.e. the Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly and Little Ice Age. The observed changes seem to be connected to general ocean atmosphere circulation changes, possibly related to North Atlantic Oscillation and Atlantic Multidecadal Oscillation regimes. Furthermore, we identify a cyclicity of 73–74 years in sea ice algae and phytoplankton productivity over the last 1.2 kyr, which may indicate a connection to Atlantic Multidecadal Oscillation mechanisms.
18. Arctic Amplification, Sea Ice Loss Not Explained By CO2 Forcing
Kim et al., 2017
Understanding the Mechanism of Arctic Amplification and Sea Ice Loss
Sea ice reduction is accelerating in the Barents and Kara Seas. Several mechanisms are proposed to explain the accelerated loss of polar sea ice, which remains an open question. … [T]he role of upward and downward longwave radiations in Arctic amplification is vague and not fully understood.
[CO2 is not mentioned in the paper as a mechanism responsible for Arctic amplification or sea ice loss.]
Long Term Changes In Arctic Region Temperatures
19. Greenland 1°C to 3°C Warmer Than Now For Most Of The Last 8,000 Years
Kobashi et al., 2017
After the 8.2 ka event, Greenland temperature reached the Holocene thermal maximum with the warmest decades occurring during the Holocene (2.9 ± 1.4 °C warmer than the recent decades) at 7960 ± 30 years B.P.
20. Arctic-Wide Temperatures Warmer Than Now During The Medieval Warm Period
Werner et al., 2017
[S]tatistical testing could not provide conclusive support of the contemporary warming to supersede the peak of the MCA [Medieval Climate Anomaly] in terms of the pan-Arctic mean summer temperatures.
21. Northern Alaska Warmer During Medieval Times
Hanna et al., 2018
Here, we utilize one such sediment archive from Simpson Lagoon, Alaska, located adjacent to the Colville River Delta to reconstruct temperature variability and fluctuations in sediment sourcing over the past 1700 years. Quantitative reconstructions of summer air temperature […] reveal temperature departures correlative with noted climate events (i.e. ‘Little Ice Age’, ‘Medieval Climate Anomaly’). … Reconstructed temperatures are generally coolest between 300 and 800 CE (Tavg = 2.24 ± 0.98°C), displaying three temperature minima centered at 410 CE (1.34 ± 0.72°C), 545 CE (1.91 ± 0.69°C), and 705 CE (1.49 ± 0.69°C). Temperatures then rapidly increased, reaching the warmest interval (800–1000 CE) in the approximately 1700-year record. During this interval, average temperatures were 3.31 ± 0.65°C, with a maximum temperature of 3.98°C.