skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 5:00 PM ET until 11:00 PM ET on Friday, June 21 due to maintenance. We apologize for the inconvenience.

Title: Arctic Sea Ice Response to Flooding of the Snow Layer in Future Warming Scenarios

The projected decline in Arctic sea ice extent as the Earth warms in response to increased greenhouse gas concentrations will occur in conjunction with increased precipitation in the Arctic, and more of that precipitation is projected to fall as rain, especially in autumn and early winter. A recently proposed method of offsetting the decline in Arctic sea ice extent would pump seawater on the sea ice surface. Either way, we envision the liquid water first infiltrating the overlying snow layer creating slush. Winter conditions would then freeze the slush to directly thicken the ice. The net reduction in insulation would increase basal growth, adding an indirect thickening effect. Simulating the response to augmented snow layer flooding gives insights that are relevant in the future Arctic with or without the implementation of geoengineering. We use a hierarchy of models to show that flooding snow on sea ice is most effective at thickening Arctic sea ice when flooding begins early in the sea ice growth season. For the geoengineering scheme to be most effective, the pumps must be deployed almost immediately, while there is still a sufficient area of sea ice over which to flood, and must continue for decades. Sea ice loss would be best mitigated if flooding is combined with reducing greenhouse gas emissions. Furthermore, the increase in rainfall over the Arctic in the 21st century is unlikely to offset a substantial portion of the loss due to warming.

more » « less
Author(s) / Creator(s):
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Earth's Future
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. This model‐based study assesses the response of the lower atmosphere and near‐surface permafrost on the North Slope of Alaska to projections in sea ice decline. The Weather Research and Forecast model, with polar optimization (polar WRF), was configured for the North Slope of Alaska and the adjacent Arctic Ocean and run for two decade‐long control periods, the 1970s and the 2040s. Community Earth System Model output was used to drive the polar WRF model. By swapping the sea ice coverage in the control cases, two polar WRF sensitivity experiments were designed to quantify the changes in the low atmosphere and near‐surface permafrost in response to projected declines in sea ice extent. The strongest impacts of sea ice decline occur primarily during the late fall and early winter. These include increases in surface air temperature, surface humidity, total cloud cover, and precipitation amount. Future impacts of sea ice decline are projected to become weaker over time in the late fall and early winter while becoming more prominent in late spring and early summer. Projected sea ice decline also inhibits low‐level cloud formation in summer as a result of destabilization of the boundary layer. Sensitivity experiments by polar WRF and Geophysical Institute Permafrost Laboratory model, respectively, suggest that sea ice decline explains approximately 20% of both the atmospheric and permafrost warmings on a mean annual basis compared to the overall projected warming under the RCP4.5 scenario.

    more » « less
  2. Abstract

    The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including reduction in sea ice extent and thickness. There are also projected increases in near‐surface Arctic wind. This study addresses how the winds trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, something that has not yet been thoroughly investigated. We analyze 50 experiments from the Community Earth System Model Version 2 (CESM2) Large Ensemble and five experiments using CESM2 with an artificially decreased sea ice roughness to match that of the open ocean. We find that with a smoother surface there are higher mean wind speeds and slower mean ice speeds in the autumn, winter, and spring. The artificially reduced surface roughness also strongly impacts the wind speed trends in autumn and winter, and we find that atmospheric stability changes are also important contributors to driving wind trends in both experiments. In contrast to the clear impacts on winds, the sea ice mean state and trends are statistically indistinguishable, suggesting that near‐surface winds are not major drivers of Arctic sea ice loss. Two major results of this work are: (a) the near‐surface wind trends are driven by changes in both surface roughness and near‐surface atmospheric stability that are themselves changing from sea ice loss, and (b) the sea ice mean state and trends are driven by the overall warming trend due to increasing greenhouse gas emissions and not significantly impacted by coupled feedbacks with the surface winds.

    more » « less
  3. Abstract

    Arctic surface warming under greenhouse gas forcing peaks in winter and reaches its minimum during summer in both observations and model projections. Many mechanisms have been proposed to explain this seasonal asymmetry, but disentangling these processes remains a challenge in the interpretation of general circulation model (GCM) experiments. To isolate these mechanisms, we use an idealized single-column sea ice model (SCM) that captures the seasonal pattern of Arctic warming. SCM experiments demonstrate that as sea ice melts and exposes open ocean, the accompanying increase in effective surface heat capacity alone can produce the observed pattern of peak warming in early winter (shifting to late winter under increased forcing) by slowing the seasonal heating rate, thus delaying the phase and reducing the amplitude of the seasonal cycle of surface temperature. To investigate warming seasonality in more complex models, we perform GCM experiments that individually isolate sea ice albedo and thermodynamic effects under CO2forcing. These also show a key role for the effective heat capacity of sea ice in promoting seasonal asymmetry through suppressing summer warming, in addition to precluding summer climatological inversions and a positive summer lapse-rate feedback. Peak winter warming in GCM experiments is further supported by a positive winter lapse-rate feedback, due to cold initial surface temperatures and strong surface-trapped warming that are enabled by the albedo effects of sea ice alone. While many factors contribute to the seasonal pattern of Arctic warming, these results highlight changes in effective surface heat capacity as a central mechanism supporting this seasonality.

    Significance Statement

    Under increasing concentrations of atmospheric greenhouse gases, the strongest Arctic warming has occurred during early winter, but the reasons for this seasonal pattern of warming are not well understood. We use experiments in both simple and complex models with certain sea ice processes turned on and off to disentangle potential drivers of seasonality in Arctic warming. When sea ice melts and open ocean is exposed, surface temperatures are slower to reach the warm-season maximum and slower to cool back down below freezing in early winter. We find that this process alone can produce the observed pattern of maximum Arctic warming in early winter, highlighting a fundamental mechanism for the seasonality of Arctic warming.

    more » « less
  4. Abstract

    Much is still unknown about the growth and physiological responses of trees to global change at the northern treeline. We combined tree‐ring width data with century‐long stable carbon and oxygen isotope records to investigate growth and physiological responses of white spruce at two treeline sites in the Canadian Arctic to concurrent increases in temperature, atmospheric CO2concentration (ca), and decline in sea ice extent over the past century. The tree‐ring records were assessed during three periods with contrasting climatic conditions: (a) the early 20th century warming, (b) the 1940–1970 cooling period, and (c) the anthropogenic late 20th century warming period. We found opposing growth trends between the two sites, but similar carbon isotope discrimination (Δ13C) and intrinsic water‐use efficiency (iWUE) trajectories. While tree growth (defined as basal area increment) increased at the site nearer to the Arctic Ocean during the 20th century following the rise in temperature and sea ice loss, growth declined after 1950 at the more interior site. At both sites, Δ13C slightly increased over these periods. However, trees showed a nonlinear response to increasedca, shifting after 1970 from a passive stomatal response (i.e., no changes iniWUE) to an active response (i.e., a moderate ∼12% increase iniWUE). Further, our isotope‐based findings do not support the idea that temperature‐induced drought stress caused the divergent growth trends at our treeline sites. This study thus highlights nonlinear and complex physiological and growth adjustments to concomitant changes in temperature, sea ice extent, andcaover the last century at the northern treeline.

    more » « less
  5. Abstract

    Over the coming century, both Arctic and Antarctic sea ice cover are projected to substantially decline. While many studies have documented the potential impacts of projected Arctic sea ice loss on the climate of the mid-latitudes and the tropics, little attention has been paid to the impacts of Antarctic sea ice loss. Here, using comprehensive climate model simulations, we show that the effects of end-of-the-century projected Antarctic sea ice loss extend much further than the tropics, and are able to produce considerable impacts on Arctic climate. Specifically, our model indicates that the Arctic surface will warm by 1 °C and Arctic sea ice extent will decline by 0.5 × 106km2in response to future Antarctic sea ice loss. Furthermore, with the aid of additional atmosphere-only simulations, we show that this pole-to-pole effect is mediated by the response of the tropical SSTs to Antarctic sea ice loss: these simulations reveal that Rossby waves originating in the tropical Pacific cause the Aleutian Low to deepen in the boreal winter, bringing warm air into the Arctic, and leading to sea ice loss in the Bering Sea. This pole-to-pole signal highlights the importance of understanding the climate impacts of the projected sea ice loss in the Antarctic, which could be as important as those associated with projected sea ice loss in the Arctic.

    more » « less