CL4.6

Poleward ocean heat transport is a key process in the earth system. Here we detail the changing northward Atlantic Water (AW) flow in the Nordic Seas and the associated Arctic Ocean heat transport and heat loss to the atmosphere since 1900, in relation to the sea ice cover. Our synthesis is largely based on a sea ice-ocean model forced by a reanalysis atmosphere (1900-2018) corroborated by a comprehensive hydrographic database (1950-), measurements of AW inflow (1996-), and other key long-term regional time series. Since the 1970s, ocean temperatures have increased in the Nordic, Barents and Polar Seas, in particular on the shelves. The AW loses heat to the atmosphere as it travels poleward, mostly in  the Nordic Seas, where ~60% of the Arctic Ocean total heat loss resides. Nordic Seas heat loss variability is large, but the long-term positive trend is small. The Barents Sea heat loss is ~30% of the total, but has larger consistently positive trends, related to AW heat transport and sea ice loss. The Arctic seas farther north see only ~10% of the  total heat loss, but show a consistently large increase in heat loss as well as decrease in sea ice since 1900. The AW inflow, the cooling of this water mass as it travels poleward, and the dense outflow have thus all increased since 1900, and they are consistently related through theoretical scaling. Some of the increased AW inflow is wind-driven, and much of the heat loss variability is linked to Cold Air Outbreaks and cyclones in the Nordic and Barents Seas. The oceanic warming is congruent with increased ocean heat transport and a loss of sea ice, and has contributed to the retreat of marine terminating glaciers on Greenland. After 2000, the warming has accelerated, creating a “new normal” that appears to also affect deep water volumes and temperature. The 20th century average Nordic, Barents and Polar Seas CO2 uptake constitutes ~8% of the global ocean, and is almost entirely driven by heat loss to the atmosphere as the AW transforms from inflow to overflow water. The total Arctic Ocean CO2 uptake has increased by ~30% since 1900, which is closely linked to the loss of sea ice in the Barents and Polar Seas.

How to cite: Smedsrud, L. H., Muilwijk, M., Brakstad, A., and Madonna, E. and the Nordic Seas Synthesis Team: Nordic Seas Heat Loss, Atlantic Inflow, and Arctic Sea Ice cover over the last century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9223, https://doi.org/10.5194/egusphere-egu21-9223, 2021.

Previous climate model studies have shown that Arctic sea ice decline can solely affect weather and climate at lower latitudes during the cold season. However, the mechanisms beneath this linkage are poorly understood. Whether sea ice loss have had an influence on the lower latitudes climate over the past decades is also uncertain (Barnes and Screen 2015). The goal of this work is to better understand the relative contributions of dyncamical and thermodynamical changes in the atmospheric response to Arctic sea ice loss, which have been suggested to oppose each other (Screen 2017). We conducted two sets of sensitivity transient experiments that allow to isolate the effect of Arctic sea ice decline on the mid-latitudes from other climate forcings, using the climate model CNRM-CM6 (Voldoire et al. 2019) in a coupled configuration or with an atmosphere-only. The first set of experiments, that is part of the European H2020 PRIMAVERA project, consists of a 100-member ensemble in which sea ice albedo is reduced to the ocean value (PERT) in the fully coupled CNRM-CM6, and which is compared to a 1950 control run (CTL) (Haarsma et al. 2016). This yields idealised ice-free conditions in summer and a more moderate sea ice reduction during the following months. The second set of experiments, that is part of the CMIP6 Polar Amplification Model Intercomparison Project (PAMIP, Smith et al. 2019), consists of a 300-member ensemble in which the atmospheric component of CNRM-CM6 is forced by sea ice anomalies associated with a future 2°C warming (FUT) and present day sea surface temperatures (SSTs). These are compared to experiments in which the atmosphere is forced by present-day sea ice conditions (PD) and the same SSTs. To extract the dynamical component of the response in the two sets of experiments, we use a dynamical adjustment method (Deser et al. 2016) based on a regional reconstruction of circulation analogs. We focus on three mid-latitudes regions in which a significant near-surface temperature response has been identified, namely North America, Europe and central Asia. We show that the cooling occurring over central Asia in both sets of experiments is dynamically-induced through an intensification of the Siberian High, and that opposed temperature responses over North America between the two sets of experiments could be explained by opposed dynamical components occurring in response to the imposed Arctic sea ice decline. Finally, we discuss whether different dynamical and thermodynamical contributions in the PAMIP multi-model experiments could explain the multi-model differences in the atmospheric response to sea ice loss.

How to cite: Chripko, S., Msadek, R., Sanchez-Gomez, E., Terray, L., Bessières, L., and Moine, M.-P.: Dynamical and thermodynamical contributions to the mid-latitude atmospheric response to Arctic sea ice decline, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15660, https://doi.org/10.5194/egusphere-egu21-15660, 2021.

Quantitative estimates of the relationship between the interannual variability of Antarctic and Arctic sea ice and changes in the surface temperature in the Northern and Southern Hemispheres using satellitedata, observational data and reanalysis data for the last four decades (1980-2019) are obtained. The previously noted general increase in the Antarctic sea ice extent (up to 2016) (according to satellite data available only since the late 1970s), happening simultaneously with global warming and rapid decrease in the Arctic sea ice extent, is associated with the regional manifestation of natural climate fluctuations with periods of up to several decades. The results of correlation and crosswavelet analysis indicate significant coherence and negative correlation of hemispheric surface temperature with not only Arctic,but also Antarctic sea ice extent in recent decades.

Seasonal and regional peculiarities of snow cover sensitivity to temperature regime changes in the Northern Hemisphere are noted with an assessment of changes in recent decades. Peculiarities of snow cover variability in Eurasia and North America are presented. In particular, the peculiarities of changes in snow cover during the autumn seasons are noted.

How to cite: Parfenova, M. and Mokhov, I. I.: Features of changes in the sea ice and snow cover extents associated with temperature changes in the Northern and Southern Hemispheres in recent decades., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6564, https://doi.org/10.5194/egusphere-egu21-6564, 2021.

The impact of Arctic sea ice decline on the weather and climate in mid-latitudes is still much debated, with observation suggesting a strong and models a much weaker link. In this study, we use the atmospheric model OpenIFS, in a set of model experiments following the protocol outlined in the Polar Amplification Model Intercomparison Project (PAMIP), to investigate whether the simulated atmospheric response to future changes in Arctic sea ice fundamentally depends on model resolution. More specifically, we increase the horizontal resolution of the model from 125km to 39km with 91 vertical levels; in a second step resolution is further increased to 16km with 137 levels in the vertical. We find that neither the mean atmospheric response nor the ensemble convergence toward the mean are strongly impacted by the model resolutions considered here.

How to cite: Streffing, J., Semmler, T., Zampieri, L., and Jung, T.: Response of Northern Hemisphere weather and climate to Arctic sea ice decline: The role of resolution in Polar Amplification Model Intercomparison Project (PAMIP) simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14735, https://doi.org/10.5194/egusphere-egu21-14735, 2021.

Over the last decades the Arctic climate change has been observed with a much faster warming of the Arctic compared to the global average (Arctic amplification) and related sea-ice retreat. These changes in sea ice can affect the large-scale atmospheric circulation over the mid-latitudes, in particular atmospheric blocking, and thus the frequency and severity of extreme events. As a step towards a better understanding of changes in weather and climate extremes over Central Europe associated with Arctic climate change, we first analyze the linkage between recent Arctic sea ice loss and blocking variability using logistic regression models. ERA5 reanalysis data are used on a monthly and seasonal time scale, and specific regional sea ice variabilities are explored. First results indicate an increased occurrence-probability in terms of blocking frequency over Greenland in summer as well as over Scandinavia/Ural in winter during low sea ice conditions. 

How to cite: Richling, A., Ulbrich, U., Rust, H., Riebold, J., and Handorf, D.: Linkage between Arctic Sea Ice Area and Atmospheric Blocking Probability over Europe using Logistic Regression Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14736, https://doi.org/10.5194/egusphere-egu21-14736, 2021.