Polar Environmental Change

Polar Environmental Change

Polar Environmental Change group includes the Centre for Polar Observation and Modeling (CPOM), and uses satellite-based observation including Cryosat-2 to monitor and understand the effects of climate change at high latitude (Giles†, Laxon†, Sammonds, Stroeve).  This group has been devastated by the untimely deaths of two outstanding researchers (Seymour Laxon and Katharine Giles) whose careers were recently honored at a session of the Living Planet Conference in Edinburgh.  

Academic Members: Prof Chris Rapley, Prof Peter Sammonds, Prof Julienne Stroeve, Dr Michel Tsamados, Dr Samantha Buzzard, Dr Harry Hoerten

Research Groups

  • Shrinking the Arctic Sea Ice

    Analysis of satellite data produced the now iconic documentation of shrinking Arctic sea ice cover (Stroeve et al., GRL 2007Stroeve et al., GRL, 2012), while radar altimetry measured circumpolar thinning of Arctic sea ice (Giles et al., GRL, 2008), and determined the contribution to sea level rise (Laxon Nature 2003,Shepherd et al., GRL, 2010).

    • Modelling the Sea Ice

      cpontest Figure 1: Observed (black line) and modeled September sea ice extent (gray and solid color lines and shading) under various emission scenarios, defined as representative concentration pathways (RCPs) in CMIP5. The numbers in parenthesis represent the number of models used in deriving the multi-model ensemble mean and the shading represents + one standard deviation.
    • Ice Conditions & Timescale

      Over the modern satellite record that begins in late 1978 to the present, Arctic ice extent exhibits downward linear trends for all months, weakest in winter and strongest for September, the end of the melt season. The downward September trend has accelerated over the past decade. Through 2001, the linear trend in September ice extent over the satellite record stood at -7.0% per decade. Through 2013, it is more than twice as large at -14.0% per decade. The seven lowest September extents in the satellite record have all occurred in the past seven years. Decreased summer ice extent has been accompanied by large reductions in winter ice thicknesses that are primarily explained by changes in the ocean’s coverage of multiyear ice (MYI). Whereas in the mid-1980s, MYI accounted for 70% of total winter ice extent, by the end of 2012 it had dropped to less than 20%. At the same time the proportion of ice older than 5 years declined from 50% of the MYI pack to less than 8%. As seasonal ice has replaced MYI as the dominant ice type, the Arctic Ocean has become more vulnerable to a “kick” from natural climate variability, initiating feedbacks that have the potential to promote a rapid transition towards a seasonally ice-free Artic state.

      There is a growing need for improved prediction of ice conditions on seasonal and longer timescales. While milder ice conditions have made the Arctic more accessible for marine shipping and resource extraction, seasonal ice conditions will still be highly variable over coming decades. The Arctic may eventually become a viable seasonal shipping route between the Atlantic and Pacific and there is value in narrowing uncertainty as to when this may occur. Finally, evolution of the sea ice cover bears directly on the evolution of surface energy fluxes and the Arctic heat budget, which can influence weather conditions both within and beyond the Arctic.

      Improved predictive capability requires improved knowledge of the spatial and temporal distribution of ice thickness. Because areas of thin ice are prone to melting out during summer, a key to seasonal prediction of regional ice severity is knowledge of the thickness in spring. Looking at longer timescales, while models participating in the latest Coupled Model Intercomparison Project (CMIP5) correctly hindcast a declining Arctic sea ice cover over the period of observations [Figure 1], the trends from most models are smaller than observed, questioning the veracity of projected trends through the 21st century. There is furthermore a large spread between models as to when essentially seasonally ice-free conditions will be reached, even with the same assumed growth rates of atmospheric greenhouse gases. While a number of factors may contribute, including inadequate representation of natural climate variability, variations in model sensitivity to external forcing, inadequate ice model physics, and errors in modeled atmospheric and oceanic forcing, representation of sea ice thickness appears to be a major issue.

  • Polar Oceanography

    Satellite observations revealed the increase of Western Arctic Ocean freshwater storage by wind-driven spin-up of the Beaufort Gyre (Giles et al., Nature Geo., 2012), and the contribution of Arctic ocean warming to reduced polar ice (Polyakov et al., JPO, 2010).

    Antarctic Ice Shelf Stability

    Experimental measurements of ice rheology in UCL cold rooms and the Hamburg large-scale ice-tank facility constrained models of the stability and potential collapse of the Larsen C ice shelf (Jansen et al., J. Glaciology, 2010; Lishman et al., JGR, 2011; Luckman et al., Crysophere, 2012).