Natural Forcing Of Arctic Climate
Increasingly Affirmed By Scientists
Three years ago a cogent paper was published in the prestigious scientific journal Nature that was surprisingly candid in its rejection of the position that the substantial warming and sea ice reduction in the Arctic occurring since the late 1970s should be predominantly attributed to anthropogenic forcing.
Dr. Quinhua Ding and 6 co-authors indicated in their paper that internal processes — natural variability associated with planetary waves and the North Atlantic Oscillation — are drivers of the recent Arctic warming and sea ice reduction, concluding that “a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.”
“Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change. The Arctic warming exceeds the global average warming because of feedbacks that include sea-ice reduction and other dynamical and radiative feedbacks. We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland. In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the North Atlantic Oscillation.”
“Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation, which is a response to anomalous Rossby wave-train activity [planetary waves related to the Earth’s rotation] originating in the tropical Pacific. Atmospheric model experiments forced by prescribed tropical sea surface temperatures simulate the observed circulation changes and associated tropospheric and surface warming over northeastern Canada and Greenland. Experiments from the Coupled Model Intercomparison Project Phase 5 models with prescribed anthropogenic forcing show no similar circulation changes related to the North Atlantic Oscillation or associated tropospheric warming. This suggests that a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.”
Since 2014, there have been several more scientific papers that have been published documenting the significance of natural forcing processes in the Arctic and how they may override a clear detection of an anthropogenic influence.
But 2017 already seems to be an exception. Papers that document the dominance of natural forcing — or that don’t even mention anthropogenic forcing as a factor in the Arctic climate processes — keep on rolling in.
As a case example, in a paper discussing the mechanisms involved in “Arctic amplification” and sea ice loss, Kim et al. (2017) never once mention anthropogenic forcing, or carbon dioxide, as mechanisms affecting the Arctic climate. In fact, in citing several other authors, they acknowledge that the physical processes involved in the forcing of Arctic climate are “subject to debate” and remain “an open question.” In other words, not only is the position that humans exert a dominant influence on the Arctic climate not “settled science”, the anthropogenic influence may be so muted a factor that it is not even worth mentioning in a paper discussing forcing mechanisms.
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. … Previous studies have proposed the physical mechanisms of Arctic amplification, which involve the effect of atmospheric heat transport (Graversen et al., 2008), oceanic heat transport (Årthun et al., 2012; Chylek et al., 2009; 10 Spielhagen et al., 2011; Onarheim et al., 2015), cloud and water vapor changes (Francis and Hunter, 2007; Schweiger et al., 2008; Park et al., 2015a; Park et al., 2015b), and/or diminishing sea ice cover (Serreze et al., 2009; Screen and Simonds, 2010a; Kim et al., 2016). The accurate physical process of the Arctic amplification, however, is subject to debate.”
“Despite the general consensus that heat transfer between the ocean and atmosphere is a crucial element in the physical mechanism of Arctic amplification and sea ice reduction, a quantitative understanding of individual contributions of heat flux components is still controversial. Further, the role of upward and downward longwave radiations in Arctic amplification is vague and not fully understood. Accurately quantifying the contribution of these different mechanisms, therefore, is required for a complete understanding of the Arctic amplification.”
[CO2 is not mentioned as a mechanism responsible for Arctic amplification or sea ice loss.]
Two months ago, Dr. Ding delivered another Nature paper — this time with 10 co-authors — that once again emphasized the Arctic’s natural variability, specifically the internal processes involved in the substantial reduction in Arctic sea ice since 1979. The scientists concluded that as much as 50% of the Arctic sea ice decline in the satellite era has been natural, and that anthropogenic forcing may play a much smaller role than has previously been assumed in climate models.
Many other newly-published papers advance the position that natural, non-anthropogenic processes are significant or even dominant factors in shaping the Arctic climate. A total of 15 are cited here categorically.
A ‘Substantial Chunk’ Of Sea Ice Loss/Warming Due To Internal/Natural Variability
“The Arctic has seen rapid sea-ice decline in the past three decades, whilst warming at about twice the global average rate. … Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30–50% of the overall decline in September sea ice since 1979. … [A] substantial chunk of summer sea ice loss in recent decades was due to natural variability in the atmosphere over the Arctic Ocean.”
“The wintertime Arctic temperature decreased from 1979 to 1997 and increased rapidly from 1998 to 2012, in contrast to the global mean surface air temperature [which] increased between 1979 and 1997, followed by a hiatus… A recent study suggests a possible role of the Pacific Ocean decadal oscillation in regulating wintertime climate in the Arctic (Screen and Francis 2016).”
“The ‘greenhouse effect’ of water vapor and clouds [CO2 not mentioned as contributing to the GHE] may amplify the effect of winds on Arctic winter climate.”
“The objectives of this study are to assess how much natural–internal variability has contributed to climate changes in these [Arctic] regions from 1979 to 2012 … In summary, the correlation analyses presented in this paper shows a natural mode of Arctic winter variability resulting from the Nordic–Siberian seesaw of meridional winds […] is associated with two-thirds of the interannual variance [cooling-warming] of winter-mean Arctic temperature between 1979 and 2012, and possibly contributed a substantial fraction of the observed Arctic amplification [1998-2012 warming] in this period.”
“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.”
Natural Planetary Waves Forcing
“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].”
“During the past three decades, the most rapid warming at the surface has occurred during the Arctic winter. By analyzing daily ERA-Interim data, we found that the majority of the winter warming trend north of 70°N can be explained by the trend in the downward infrared radiation (IR). This downward IR trend can be attributed to an enhanced poleward flux of moisture and sensible heat into the Arctic by poleward propagating Rossby waves, which increases the total column water and temperature within this region. This enhanced moisture flux is mostly due to changes in the planetary-scale atmospheric circulation rather than an increase in moisture in lower latitudes.”
Solar Forcing Of Arctic Climate, Sea Ice Trends
“Correlations between paleotemperature records from the North Atlantic and solar activity suggest that changes in solar output may cause significant shifts in the climate of the North Atlantic region. To test the role of solar activity on summer SST at our study site in West Greenland, we conducted a cross-correlation analysis between our reconstructed summer SST record and a total solar irradiance (TSI) series. The results indicate that the maximum correlation coefficient (0.284) of summer SST [sea surface temperatures] and TSI [total solar irradiance] records is obtained at nearly zero time-lag (-6 time-lag), which means that variations in solar activity affected the summer SST variability in the study area. … A significant positive relationship between summer SSTs on the North Icelandic shelf and solar irradiance reconstructed from 10Be and 14C records during the Holocene was also demonstrated by Jiang et al. … Spectral analyses indicate that significant centennial-scale variations are superimposed on the long-term orbital trend. The dominant periodicities are 529, 410, and 191 years, which may be linked to the well-known 512- and 206-year solar cycles. Cross-correlation analyses between the summer SSTs and total solar irradiance through the last 5000 years indicate that the records are in phase, providing evidence that variations in solar activity impacted regional summer SST variability. Overall, the strong linkage between solar variability and summer SSTs is not only of regional significance, but is also consistent over the entire North Atlantic region.”
“The causes that are controlling the decrease in sea ice are still under discussion. In several studies changes in extent, thickness and drift of Arctic sea ice are related to changes in the overall atmospheric circulation patterns as reflected in the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). The NAO and AO are influencing changes of the relative position and strength of the two major surface-current systems of the Arctic Ocean. … The increase in sea ice extent during the late Holocene seems to be a circum-Arctic phenomenon, coinciding with major glacier advances on Franz Josef Land, Spitsbergen and Scandinavia. The increase in sea ice may have resulted from the continuing cooling trend due to decreased solar insolation and reduced heat flow from the Pacific. … The increase in sea ice extent during the late Holocene seems to be a circum-Arctic phenomenon as PIP25-based sea ice records from the Fram Strait, Laptev Sea, East Siberian Sea and Chukchi Sea display a generally quite similar evolution, all coinciding with the decrease in solar radiation … The main factors controlling the millennial variability in sea ice and surface-water productivity are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation, whereas short-term centennial variability observed in the high-resolution middle Holocene record was possibly triggered by solar forcing.”
“The reconstruction indicates warm conditions with reduced sea-ice cover, associated with the Holocene Thermal Maximum, from ca. 6700 to 5000 cal. yr BP. … A distinct increase in sea-ice cover began at 1750 cal. yr BP, with absolute maximum values during the last millennium. … In order to assess the contribution of different potential forcing factors to sea-ice conditions off West Greenland, we evaluated the relationship between our sea-ice reconstruction and solar activity, as well as with the strength of ocean circulation. The observed agreement between the sea-ice record and solar activity suggests that solar forcing may have been an important trigger for sea-ice variability off West Greenland during the last 5000 yr.”
Pacific Decadal Oscillation (PDO) Forcing
“This paper investigates an annually-laminated (varved) record from the western Canadian Arctic and finds that the varves are negatively correlated with both the instrumental Pacific Decadal Oscillation (PDO) during the past century and also with reconstructed PDO over the past 700 years, suggesting drier Arctic conditions during high-PDO phases, and vice versa. These results are in agreement with known regional teleconnections, whereby the PDO is negatively and positively correlated with summer precipitation and mean sea level pressure respectively. This pattern is also evident during the positive phase of the North Pacific Index (NPI) in autumn. Reduced sea-ice cover during summer–autumn is observed in the region during PDO− (NPI+) and is associated with low-level southerly winds that originate from the northernmost Pacific across the Bering Strait and can reach as far as the western Canadian Arctic. These climate anomalies are associated with the PDO− (NPI+) phase and are key factors in enhancing evaporation and subsequent precipitation in this region of the Arctic.”
Cloud Radiative Forcing
“A number of feedbacks are found that damp the warming effect of the clouds. Thin mixed-phase clouds increase the downward longwave fluxes by 100 W m−2, but upward daytime surface longwave fluxes increase by 20 W m−2 (60 W m−2 at night) and net shortwave fluxes decrease by 40 W m−2 (partially due to a 0.05 increase in surface albedo), leaving only 40 W m−2 available for melt. This 40 W m−2 is distributed between the turbulent and conductive ground fluxes, so it is only at times of weak turbulent fluxes (i.e., at night or during melt) that this energy goes into the conductive ground flux, providing energy for melt. From these results it is concluded that it is the integrated impact of the clouds over the diurnal cycle (the preconditioning of the snowpack by the clouds at night) that made melt possible during this 3-day period. These findings are extended to understand the pattern of melt observed over the GIS. … Mixed-phase clouds are common at Summit (Shupe et al. 2013) and play a critical role in the Arctic surface energy balance (Shupe and Intrieri 2004), radiatively warming the highly reflective surface at Summit year-round (Miller et al. 2015).”
Most Of The Arctic’s Net Warming Occurred Before 1950
The instrumental record (HadCRUT) for Arctic temperatures indicates that there has been no significant net warming in the Arctic during the last ~80 years. Newly published papers also affirm that much of the warming of the Arctic occurred before 1950, or before humans began emitting CO2 in large quantities.
“During the MCA [Medieval Climate Anomaly], the contrast between reconstructed summer temperatures over mid- and high-latitudes in Europe and the European/North Atlantic sector of the Arctic shows a very dynamic expression of the Arctic amplification, with leads and lags between continental and more marine and extreme latitude settings. While our analysis shows that the peak MCA [Medieval Climate Anomaly] summer temperatures were as high as in the late 20th and early 21st century, the spatial coherence of extreme years over the last decades seems unprecedented at least back until 750 CE. However, statistical testing could not provide conclusive support of the contemporary warming to supersede the peak of the MCA in terms of the pan-Arctic mean summer temperatures.”
“The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts.”
“The trend in Western Tungnahryggsjökull during the first half of the 20th century was a more rapid retreat, showing the highest average rates of the whole period (19.5 m yr−1). By 1946, this glacier had retreated almost 90% of the total recorded between the LIA maximum (1868) and 2005.”