Scientists have increasingly determined that today’s Arctic sea ice concentrations are still much higher than they have been most of the last several thousand years, undermining claims that modern era Arctic sea ice changes are remarkable, unusual, or unprecedented.
In the graphical illustration of Late Holocene West Greenland sea ice changes shown above, Kolling and colleagues (2018) indicate that both present-day and Little Ice Age era (~1300s to 1800s AD) sea ice does not melt until May, or late spring (Fig. 6a).
During most of the last 2,200 years — especially during the Medieval Warm Period (MWP) and Roman Warm Period (RWP) — spring sea ice melted in March, two months earlier than today (Fig. 6b).
The authors attribute the lower-than-today sea ice concentrations and warmer temperatures during the MWP and RWP to a “self-amplifiying system” involving variations in solar activity and the AMO. Atmospheric CO2 concentrations are not mentioned in the paper as a factor influencing sea ice changes.
“The period between 2.2 and 1.2 kyr BP, with lower than modern sea ice conditions in Disko Bugt (Fig. 6b), coincides with generally warm conditions over the Greenland Ice Sheet.”
“A self-amplifying system may have caused the environmental changes observed in Disko Bugt area as follows: solar triggered Arctic sea ice melt [Ruzmaikin et al., 2004] increases freshwater supply towards the North Atlantic causing a reduction in sub-polar gyre activity and AMO [Holland et al., 2001, Schmith et al., 2003] as described by Sha et al. [2016].”
Consistent with other reconstructions for the region (Kryk et al., 2017; Durantou et al., 2012; Yamamoto et al., 2017; Perner et al., 2018), proxy evidence shows that current sea ice conditions are perhaps only modestly changed from the indicated conditions during the past few centuries.
The lack of any unusual or remarkable change in sea ice conditions during the modern era relative to the past suggests there is a lack of conspicuous connection between rising anthropogenic CO2 emissions and the Arctic climate.
New insights into sea ice changes over the
past 2.2 kyr in Disko Bugt, West Greenland
“Our biomarker record indicates that Disko Bugt [West Greenland] experienced a gradual expansion of seasonal sea ice during the last 2.2 kyr. Maximum sea ice extent was reached during the Little Ice Age around 0.2 kyr BP. Superimposed on this longer term trend, we find short-term oscillations in open water primary production and terrigenous input, which may be related to the Atlantic Multidecadal Oscillation and solar activity changes as potential climatic trigger mechanisms.
“The period between 2.2 and 1.2 kyr BP, with lower than modern sea ice conditions in Disko Bugt (Fig. 6b), coincides with generally warm conditions over the Greenland Ice Sheet.”
“Overall, IP25 concentrations remained relatively low and constant until 1.2 kyr BP, followed by a gradual increase (Fig. 3e). The lowest [sea ice] concentrations, around 0.06 µg/gTOC, are observed in the lowermost core section from 2.2 to 1.5 kyr BP (Fig. 3e).”
“During the last 0.1 kyr, all biomarker concentrations showed an increase, brassicasterol and HBI III reach maximum values in the uppermost sample(80 µg/gTOC and 1.8 µg/gTOC, respectively; Fig. 3b, d).”
“[During the Little Ice Age (0.7–0.2 kyr BP)] our biomarker record supports harsher sea ice conditions, possibly similar to conditions as observed today (Fig. 6b), indicated by strong increased in IP25 concentration and the PDIP25 index (Fig. 4c, d).”
“AMO variability has been linked to solar activity changes [Knudsen et al., 2011]. Changes in incoming radiation may influence sea ice extent and the Greenland Ice Sheet behaviour [Ruzmaikin et al., 2004] and consequently affect the freshwater discharge/inflow [Schmith et al., 2003] and nutrient availability to the area. A self-amplifying system may have caused the environmental changes observed in Disko Bugt area as follows: solar triggered Arctic sea ice melt [Ruzmaikin et al., 2004]increases freshwater supply towards the North Atlantic causing a reduction in sub-polar gyre activity and AMO [Holland et al., 2001, Schmith et al., 2003] as described by Sha et al. [2016]. This may in turn cause distinct changes in WGC composition and meltwater supply from the Greenland Ice Sheet that affects phytoplankton blooms in West Greenland.”
“We find that the Disko Bugt area was influenced by seasonal sea ice over the last 2.2 kyr BP. The overall sea ice trend indicates a development from a reduced sea ice cover during early spring, with sea ice algae productivity hampered by light availability to a gradual extend of the sea ice season from 1.2 kyr BP onwards. This change in sea ice extend is parallel to decreasing Northern Hemisphere atmospheric temperatures and culminates in the Little Ice Age around 0.2 kyr. We assume that modern conditions, with sea ice present until late spring and the presence of a stable ice edge at Disko Bugt, established around that time [~200 years ago].”