U24B-01 INVITED
Arctic Sea Ice in 2008: Standing on the Threshold
Perhaps the most visible sign of global climate change is the Arctic's rapidly shrinking sea ice cover. Concerns are growing that we are approaching a "tipping point", beyond which there is rapid transition to ice- free Arctic Ocean in summer. Sea ice extent in September 2007 was the lowest recorded over the satellite era, and likely the lowest in at least a century. Could summer 2007 have been the tipping point? Given this possibility, eyes of the polar community focused on 2008. Would ice extent this summer set another record low, or would there be a recovery? Satellite data revealed that much of Arctic Ocean in spring 2008 was covered by fairly thin, first-year ice, vulnerable to melting out in summer. Coupled with indications of early spring melt, the stage was set for dramatic summer sea ice losses, rivaling or even exceeding those of 2007. However, by July, we had fallen well off the record pace. While there was no doubt that the summer ice minimum would be well below average, setting a new record seemed unlikely. Thinking started to change in August, when the daily rate of ice loss, instead of slowing in response to seasonal cooling of the Arctic, maintained a brisk and fairly steady value, largely due to pronounced ice melt in the Chukchi and East Siberian Seas. By late August, and with several weeks still left in the melt season, ice extent had fallen to the second lowest level yet recorded in the satellite era. As of this writing, in early September, we were closing in on the 2007 record.
U24B-02 INVITED
Summer 2007 and 2008 Arctic Sea Ice Loss in Context: OUTLOOK 2008
The Arctic is changing faster than the publication cycle for new information. In response, the SEARCH and
DAMOCLES Programs initiated an OUTLOOK 2008 to provide broad-based communication and assessment
within the arctic science community on the causes of rapid summer sea ice loss, synthesizing information
from Arctic observing networks and model simulations. The question for summer 2008 was whether the
previous loss of multi-year sea ice and delay in sea ice formation in autumn 2007 would still allow sufficient
winter growth of sea ice thickness to last through the summer 2008, potentially allowing for recovery from the
2007 minimum. The answer is no; summer 2008 was a second sequential year of extremely low minimum sea
ice extent. To organize OUTLOOK 2008, respondents were asked in May, June and July to provide a
rationale and semi-quantitative assessment of arctic sea ice extent anticipated for September 2008.
OUTLOOK 2008 supplemented information maintained by ice centers, universities and other data providers.
Using a range of methods, all of the approximately 20 groups responded that summer sea ice would not
return to climatological mean conditions, with a median response near the 2007 extent. The range of
responses depended on the relative weight given to "initial conditions," e.g., age and thickness of sea ice at
the end of spring, versus whether summer winds in 2008 would be as supportive for ice loss as in 2007. Initial
conditions turned out to be a primary factor for summer 2008, with implications for continued sea ice loss in
future years. OUTLOOK 2008 highlighted aspects of the observation and modeling efforts that require
further attention such as interpretation of summer microwave signatures, in situ buoy measurements, and
data assimilation in models. We appreciate the contributions from respondents and reviewers who made
OUTLOOK 2008 a success.
http://www.arcus.org/search/seaiceoutlook/index.php
U24B-03 INVITED
Short-lived Pollutants in the Arctic: Climate Impacts and Temporal Trends
Several short-lived pollutants known to impact Arctic climate may be contributing to the accelerated rates of warming observed in this region relative to the global annually averaged temperature increase. These species include methane, tropospheric ozone, and tropospheric aerosols. Model calculations show that the forcings due to black carbon, methane, and tropospheric ozone lead to a positive surface temperature response indicating the need to reduce emissions of these species within and outside the Arctic. Additional aerosol species may also lead to surface warming if the aerosol is coincident with thin, low lying clouds. Forcing mechanisms and the resulting surface temperature response for the short-lived pollutants will be described. In addition, the long range transport of pollutants to the Arctic, their temporal trends within the Arctic, and relevant results from recent IPY field campaigns will be presented.
U24B-04 INVITED
Forcing agents driving rapid Arctic climate change
Observations show a much faster warming in the Arctic than at lower latitudes during recent decades. Amplification of global warming in the Arctic is a well-known phenomenon resulting primarily from feedbacks whereby warmer temperatures reduce snow and ice cover, decreasing the Earth's reflectivity (albedo) and thus enhancing warming. While the impact of increasing abundances of well-mixed greenhouse gases dominates Arctic warming, short-lived species also appear to play an important role. Aerosols have a large effect on radiative fluxes in the Arctic, sometimes opposite to their effect at lower latitudes, and deposition of black carbon (BC) darkens snow and ice surfaces, also leading to radiative perturbations. Additionally, tropospheric ozone has been shown to play an important role in seasonal Arctic warming trends. I will discuss how short-lived pollutants are transported to the Arctic and present an overview of measurements and modeling of the effects of both long-lived and short-lived pollutants on the Arctic. In addition to comparing the impact of these various climate forcing agents, I will discuss the relative importance of local and remote radiative forcing. I will highlight the many uncertainties that remain in our understanding, especially for aerosol-cloud interactions. Finally, I will compare the observed historical surface temperature record with model results and demonstrate that greenhouse gas and natural forcings alone cannot account for the measured trends. Taking into account climate model estimates of unforced variability, these results are consistent with a substantial role for short-lived pollutants in Arctic climate trends.
U24B-05 INVITED
Fire and Ice: Surprises in a Warming Arctic Land Surface
Long term predictions based on short-term observations are a notoriously risky enterprise. In arctic tundra landscapes, as in many complex systems, long-term change is rarely a linear or monotonic process. More often than not major changes in system state occur abruptly, along trajectories that are unpredictable from knowledge of short-term process controls. Examples of such changes can be found in long-term experimental manipulations to both terrestrial and aquatic ecosystems near Toolik Lake, Alaska, and in responses to natural and anthropogenic disturbances including a recent, very large tundra wildfire. Monitoring of these manipulations and disturbances over many years invariably leads to surprises that would not have been observed in relatively stable arctic ecosystems. One specific example is the interaction between climatic warming, shrub abundance in tundras, soil nutrient turnover, and permafrost.
U24B-06
Rapid Arctic Change: Mapping the Extent of Change on Human Systems
Human system changes tied to the loss of sea ice and other arctic changes are have been observed across the entire range of human activities both in the arctic and elsewhere. The specific nature of a particular impact may be understood within a framework organizing human systems along three dimensions: time, space, and category. Three temporal scales may be recognized: short-term or "reactive" – covering immediate threats to life, mid-term or "proactive" – covering seasonal level concerns, and the planning – covering long-term threats to viability. Similarly, four spatial scales may be recognized: local, regional, national, and international. Among many others, five main categories of response are considered: individual, cultural, regulatory, food systems, political, and scientific. This framework allows us to structure discussion of changes and impacts. From the myriad we have identified three examples that provide snapshots of this spectrum: 1) The Bering Sea fisheries of Unalaska. This is a commercial/subsistence mixed culture/food system strongly impacted by national regulations on a short and mid-term time frame. 2) Impacts on food systems, infrastructure, transportation and economy from the loss of sea ice to in the Alaska Native subsistence community of Shishmaref, and 3) National and international scale changes resulting from increased scientific understanding and media coverage of a changing arctic.
U24B-07 INVITED
Lessons learned from the 2007 Arctic sea ice loss
Arctic sea ice is melting at unprecedented rates. Our work evaluates the atmospheric forcing on recent
Arctic sea ice loss using satellite, ground-based, and reanalysis datasets. Here, we will focus on the 2007
melt season and the perspective gained after one year of additional observations and research. Recent
studies have shown that the 2007 ice loss was driven both by the presence of vulnerably thin ice and the
thermodynamic and dynamic forcing associated with an unusually strong anti-cyclonic atmospheric circulation
pattern. The implications of the 2007 ice loss for future ice loss are only now becoming evident. During the
2008 melt season, relatively benign radiation and wind patterns produced tremendous ice melt, suggesting
that the ice is now in a much more vulnerable state. We present spatial-temporal fingerprinting analyses that
helps constrain the contribution of dynamic and thermodynamic forcing to the 2007 sea ice loss. We show
that early summer melt was driven primarily by thermodynamic factors, while late summer melting was driven
more by dynamic factors. We also use satellite and reanalysis data sets (NCEP, JRA) available through 2008
to address the extent to which the 2007 atmospheric forcing was anomalous. We show that the 2007
atmospheric circulation pattern was highly unusual, especially when compared to patterns that have occurred
in the recent past.
http://www.cgd.ucar.edu/cms/jenkay/
U24B-08 INVITED
Toward understanding the role of the atmosphere in pan Arctic change and sea ice loss; an update on the status of focused campaigns under POLARCAT.
Sea ice loss reached an extraordinary extent in 2007, decreasing in area more than 2.5 million square
kilometres below the 1979 extent. Sea ice loss is one of many Arctic processes resulting from a warming
climate. The dynamics of a changing Arctic system are particularly sensitive to climate change and filled with
uncertainties and complex feedback mechanisms - most being simply unknown.
During the International Polar Year (IPY) a number of international partnerships were formed to establish the
Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry,
Aerosols, and Transport (POLARCAT). Under the umbrella of POLARCAT projects cooperated with national
funding to undertake the most comprehensive assessment of air pollution impacts on the Arctic to date. In the
spring and summer of 2008 more than 20 institutes from ten nations participated in intensive aircraft, ship,
and station-based campaigns with accompanying efforts from the satellite and modelling communities to
provide near real time products for mission planning and analysis.
The campaigns provided an assessment of the role that tropospheric chemistry, aerosols, and transport play
in the Arctic. The spring campaigns focused on anthropogenic pollution, while the summer campaigns
targeted biomass burning. During the spring of 2008, over 80 flights were flown by five different aircraft as
part of the ARCTAS, ISDAC, ARCPAC, and French POLARCAT campaigns, the ICEALOT campaign
commissioned the R/V Knorr to travel over 12,000 km, and numerous specialty satellite and modelling
products were developed with near real time distribution. These same products were again used for flight
planning and forecasting in the summer when an additional 50+ flights were flown by the ARCTAS, French
POLARCAT, Siberian YAK, and GRACE campaigns. Several ground based stations and the Siberian
TROICA campaign also conducted intensive operating periods (IOPs). We present an overview of the
individual campaigns, anticipated products, and initial "quicklooks"
from these activities.
http://www.polarcat.no
U24B-09 INVITED
Rapid Arctic change and implications for sea-ice use and its management at the local and regional level: An example from Alaska
Reductions in sea-ice thickness and summer extent over the past few decades have been particularly pronounced in Alaska. This rapid environmental change coincides with significant socio-economic transformations, including increased ship traffic and offshore oil and gas development. Adaptation and response to these changes and regulation of coastal and offshore activities require environmental data and projections on seasonal to decadal timescales. Nascent Arctic observation networks are of great potential value in this context. However, in order for such observing and associated modeling activities to be useful, several criteria have to be met: (1) observations need to be relevant to stakeholders adapting or responding to a changing ice regime, (2) data products need to be accessible and interpretable by those they are meant to serve, and (3) institutions and governance strategies need to be in place to allow effective utilization of environmental data and information on changing ice conditions. We show how the concept of sea-ice system services can help guide observing programs, in particular in situations with conjoined uses of the ice cover. An example from our work in Arctic Alaska illustrates this concept for the use of sea ice as a platform by indigenous hunters, industry and marine mammals. Adaptive responses by different user groups to the substantial variability observed in local-scale ice conditions will require a significant effort in downscaling standard sea-ice data products and integrating new types of measurements. The challenge for ice-covered waters is that current approaches governing utilization of the sea-ice environment may not always be effective in addressing conjoined, potentially conflicting uses. The major transformations underway in the Arctic now provide us with an opportunity to explore and evaluate different approaches of observing, adapting and responding to change.
U24B-10 INVITED
Assessing Arctic sea ice predictability - from seasons to centuries
The Arctic is undergoing rapid environmental change and information on future sea ice conditions, from seasonal variability to secular trends, is critical for our ability to respond to these events. However, the inherent short-term predictability of Arctic sea ice may well be altered with a changing climate. Additionally, projections of sea ice differ widely across climate models suggesting questionable skill in our ability to predict long-term rates of future ice loss. Here we examine the potential predictability in Arctic sea ice across multiple temporal scales. The implications of a rapidly changing Arctic state for the skill in seasonal forecasting are analyzed, including the varying importance of a number of possible predictors and the roles of preconditioning of the sea ice versus intrinsic synoptic scale variations. The possibility of decadal predictability in the ice cover is assessed in the context of climate model simulations. Finally, reasons for the wide spread in model projections of secular arctic change are discussed and recent improvements in polar processes for the next generation Community Climate System Model are highlighted.