(2012) THE ARCTIC’S RAPIDLY SHRINKING SEA ICE COVER: A RESEARCH SYNTHESIS PRESENTATION Zachary Looney 2 nd Year Atmospheric Sciences

AUTHORS  J. C. Stroeve· M. C. Serreze · A. P. Barrett National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Boulder CO, USA  M. M. Holland · J. E. Kay National Center for Atmospheric Research, Boulder CO, USA  J. Malanik Colorado Center for Astrodynamics Research, University of Colorado, Boulder, Boulder CO, USA

OVERVIEW  September extent and thickness of artic sea ice reaching new minima  Thinner, first year ice is increasingly accounting for more of the amount of post winter sea ice extent  Thanks to different feedbacks, climate forcing is pushing artic sea ice extent towards an increasingly non-linear decline  Could the rate of loss of artic sea ice be accelerating towards a tipping point threshold?

WHAT IS ARTIC SEA ICE  Artic sea ice extent grows over the late fall and winter months  Sea ice extent declines with the late spring and summer months

THICK VS THIN SEA ICE  Thin first-year ice is accounting for more and more of spring sea ice extent  Has grown from 38% in the early 1980s to 72% in spring 2008, following the dramatic September sea ice minimum of 2007 (Stroeve et al)  Decreasing age of sea ice points toward less resistance to seasonal factors  Also works to confirm the overall loss of sea ice in the past 50 years

MEASUREMENTS USED AND DATA SOURCES  The National Snow and Ice Data Center provided data for daily and monthly fields of sea ice concentration with a 25km spatial resolution.  Derived from Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) brightness temperatures using the NASA Team sea ice algorithm (Cavalieri et al.1996; Meier et al. 2006)  Defining Artic sea ice age also relied on a series of satellite passive microwave, visible and thermal imagery and drifting ocean buoys.  Surface air temperature, sea level pressure and absorbed solar radiation data were taken from the Japanese Meteorological Society and NASA A- Train satellites

THE OVERALL DECLINE

THE INCREASING DECLINE  According to the authors, the slope of decline for the best lines of fit for loss of sea ice extent between the period1979 to 1998 and 1999 to 2010 grew by ~0.122 million square kilometers per year.  This difference was found to be statistically significant to a confidence level of 95%

WHAT DOES THIS MEAN?  The authors claim that this accelerating declining trend is hastening the transition to a potential Artic cryosphere with only seasonal sea ice  The difference between thin and thick sea ice, seasonal factors, and external climate forcings are continuing and enhancing this trend.

THE DOWNFALLS OF FIRST YEAR ICE  Most of thin first year ice melts with the summer months  The thinner the ice the less resistance it has to abnormally warm winters of summers  Self-enhancing process

DOWNFALLS CONT’D  The growing amount of susceptible first-year ice results in more open ocean water during the summer months  Results in decreasing overall albedo  Works as a positive feedback loop, the less albedo overall the less returning sea ice observed

CUMULATIVE SUMMER ANOMALIES FOR SOLAR ENERGY ABSORPTION

WARMING TEMPERATURES  Historically positive temperature anomalies have been followed negative anomalies, helping the Artic sea ice system to recoup its loses  However, seen in this temperature data from the Japanese Meteorological Society analyzed by the authors, since 2000 warm anomalies dominate all months

EFFECTS OF DIFFERENCE IN SEA LEVEL PRESSURE AND SEASONAL ARTIC WEATHER  Weather patterns across the artic circle have an important impact on how much sea ice is formed or melted  The phase of the Artic Oscillation between negative and positive have an important effect on how far north weather systems can go and on whether cold polar air will be able to affect systems to the south  Cloud coverage is clearly an important factor for changing Artic albedo. Seasons dominated by high pressure systems will allow in more solar radiation

2007 SEPTEMBER SEA ICE MINIMUM EVENT  According to the paper, the “The dramatic September ice extent minimum of 2007 occurred after years of shrinking and thinning of the ice cover linked to natural variability and external forcing, making the ice cover increasingly vulnerable to an anomalous atmospheric event”  The factors previously described set up the minima event, which with unfavorable atmospheric patterns over the 2007 summer for sea ice retention lead to a record smashing minimum

SUMMER 2007  Recently this pattern has been termed the summer Arctic Dipole Anomaly (DA; Wu et al. 2006; Overland et al. 2008; Wang et al. 2009)  Characterized by unusually low pressure over Siberia and high pressure over the Canadian Basin, it set up in early July 2007 and persisted through the summer.  Strong southerly winds over the Siberian sea warmed the Artic and pushed ice toward the pole  The region of abnormally high pressure also saw an anomalous lack of cloud coverage over the region, allowing more solar radiation through  Results are unprecedented summer melting of Artic sea ice

ARTIC DIPOLE ANOMALY

THE QUESTIONS RAISED  With increasingly little September Artic ice coverage, the Artic cryosphere is made more susceptible to seasonal anomalies like that in Will the system be able to survive the next summer anomaly or will it be pushed pass its threshold?

CHANCE FOR RECOVERY?  The authors theorize that this combination of warming surface temperatures, decreasing albedo, and declining age of sea ice all work to hinder any chance for recovery of Artic sea ice  Now even a year with an abnormally cold winter would be able to do little on it’s own to reverse the trend

WHERE DOES THIS LEAVE THE FIELD?  The authors point out that one of the most important and not well understood factors is the transfer between the ocean and the boundary layer of thermal energy  The effects of positive or negative thermal forcing and how they will develop need more research done

POTENTIAL CONSEQUENCES  While the paper didn’t specify much in the way of potential consequences to the accelerating decline of Artic Sea Ice, some obvious ones come to mind  Disruption of the Thermohaline Circulation  Disruption of cold deep water formation

QUESTIONS?