GC44A-01 16:00h
Arctic Change Detection: Multiple Observations and Recent Explanations
The recently released Arctic Climate Impact Assessment (ACIA) Report documents Arctic-wide changes and impacts; it provides a long-term perspective for peoples, governments and scientists in coping with these changes. Further, investigation of the last three decades of multivariate biophysical data sets(climate, land and marine ecosystems, cryosphere) and century-long weather records, show two main types of Arctic variability. These are: 1) long-term trends as represented by loss of sea-ice and tundra area and their biological response, and 2) decadal variability in atmospheric forcing and its direct impacts. Three main conclusions are possible: * Temperature anomalies in the last 15 years are unique in the Arctic instrumental record (1880-2003). Historically, there were regional/decadal warm events during winter and spring in the 1930s to 1950s, but meteorological analysis shows that these surface air temperature anomalies are the result of intrinsic variability in regional flow patterns, as contrasted with the Arctic-wide Arctic Oscillation (AO) influence of the 1990s. * These changes are primarily driven by changes in atmospheric circulation, and thus are subject to north/south gradients in hemispheric radiative forcing from volcanic aerosols, insolation cycles and CO2 increase. These north/south differences drive temperature advection in the trough-ridge structure of the AO. This conclusion is based primarily on model results and impacts from volcanos. * Change is likely to be irreversible over at least the next decade. In the previous five years, many ecosystems, such as the Bering Sea and east Greenland, are showing more year-to-year persistence, despite considerable variability in the AO and other climate indices. We hypothesize that the changes occurring in the Arctic are beginning to be significant enough to make the Arctic less sensitive to cold swings in atmospheric variability, although direct mechanisms are unclear. A next step in the post-ACIA period is a comprehensive Arctic Change Detection product which builds upon the ACIA report with regularly updated information. Credibility is based on multiple lines of evidence and cooperation of scientists. The Arctic Change Detection project provides a near-realtime suite of indicators, their potential impacts, recent events, news items, and scientific publications, in an understandable format at www.arctic.noaa.gov. This website makes information about the current status of the Arctic available to a wide audience.
http://www.arctic.noaa.gov
GC44A-02 16:15h
Multi-proxy extension of the winter temperature record from Svalbard Airport
The homogenized Svalbard Airport temperature record (1912-present) is one of only a few long-term ($>$65 yr) instrumental records from the high Arctic. The early part of the record shows a dramatic increase in temperature around 1918, the so-called early 20th century warming. We present an extended Svalbard Airport winter record obtained using newly digitised meteorological observations from thirteen winters in the interval 1872-1915, and three proxy records: ice-core oxygen isotope data from the high-resolution 1997 Lomonosovfonna ice core; the Barents Sea ice-edge record, and the Vard$\o$, Norway temperature record. Our results suggest that a gradual warming on Svalbard started in the 1800s, and that the apparent step-change in Svalbard climate is simply part of an overall warming trend, which we estimate to be somewhere between 0.015-0.025 \deg C yr$^{-1}$ for the period 1860-1995, in line with borehole estimates. Newly available daily meteorological observations at Green Harbour show that the early 20th century warming on Svalbard is associated with an decreased occurrence of clear sky conditions and resultant inversions. Increased cloud cover accounts for about 2/3 of the observed temperature increase in the early 20th century warming at Svalbard Airport.
GC44A-03 16:30h
Is Global Warming Melting the Greenland Ice Sheet?
Concerted observational and modelling programmes are underway to determine the mass balance of the Greenland Ice Sheet, and therefore help predict its response to future climatic change. We present results of meteorological modelling based on ERA-40 reanalysis data from the European Centre for Medium Range Weather Forecasts (ECMWF). Our novel surface-mass-balance history of the ice sheet for 1958-2003, is based on accumulation (snowfall minus evaporation/sublimation) modelling and a new monthly melt-water runoff model by Janssens & Huybrechts (Huybrechts 2002). These techniques combined yield valuable insights into the past and present state and variability of the Greenland ice mass and links with climate. Aspects of the validation of the new accumulation, runoff and SMB series are discussed. There was considerable interannual variability in snow accumulation, runoff and mass balance over the last 46 years. By comparing with long-term temperature, precipitation and accumulation records from the meteorological stations and ice cores, we discuss possible climatic factors forcing the ice in this period. There are distinct signals in runoff and SMB following three major volcanic eruptions. Runoff losses from the ice sheet were 280(±28) km^3 yr^-1 in 1961-90 and 391(+-39) km^3 yr^-1 in 1998-2003. Significantly rising runoff since the 1990s has been partly offset by more precipitation. However, our best estimate of overall mass balance declined from -3(±53) km^3 yr^-1 in 1961-90 to -65(±61) km^3 yr^-1 in 1998-2003. Additional dynamical factors that cause an acceleration of ice flow near the margins, and possible enhanced iceberg calving, may have led to a more negative mass balance in the past few years than suggested here. The implication is a significant and accelerating recent contribution from the ice sheet, about 0.22 mm yr^-1 over the last six years, to global sea-level rise. Runoff and thinning of the ice-sheet margins increased substantially since the 1990s. However, massive snow accumulation over south-east Greenland during winter 2002/03, well shown in our analysis, led to unprecedented thickening in recent NASA aircraft LIDAR surveys. Do these recent changes indicate more extreme weather conditions including warming over the Ice Sheet, more storminess and higher accumulation events, due to global warming?
GC44A-04 16:45h
Does the PDO Affect the Climate over Greenland and Complicate the Reconstruction of NAO Variability from Ice Core Records?
Efforts to use ice core paleoclimate histories to extend the record of North Atlantic climate variability, characterized as the North Atlantic Oscillation (NAO), have met with mixed results. An expanded data set of annually resolved, multi-century records, reveals that the relationship between NAO variability and annual accumulation over Greenland varies both spatially and temporally. Prior to 1925 when the amplitude of the NAO was large and its periodicity was more regular, its influence on accumulation was strongest in west central Greenland (r = -0.735, sig. $>$ 95%). As the NAO weakened and became less periodic (i.e., from 1925 to 1960), its influence on accumulation shifted to southeastern Greenland (r = -0.497, sig. $>$ 95%). A preliminary investigation of the relationship between the variability in the Pacific Decadal Oscillation (PDO) and ice-core derived annual $\delta$$^{18}$O and accumulation histories (1900 to 1999 A.D.) suggests that the PDO may exert a greater influence on North Atlantic climate variability than hitherto considered. The cool season (Nov. - Mar.) PDO and annual accumulation in southern Greenland were strongly correlated (r = -0.680, sig. $>$ 95%) prior to 1945. In 1945 the PDO changed from a warm to a cool phase and thereafter the relationship with accumulation weakened. Most intriguing is the strong positive relationship between the cool season PDO and annual average $\delta$$^{18}$O that characterized the region stretching from the central summit (GISP2) to the northwest (GITS) prior to 1945. After the Pacific phase change in 1945, the statistically significant relationship between $\delta$$^{18}$O and PDO shifted southeast and changed sign (negative). These observations suggest a century scale north-south seesaw in the influence of PDO on the $\delta$$^{18}$O signature in Greenland precipitation, but confirmation awaits reconstruction of a longer PDO history.
GC44A-05 17:00h
Antarctic Peninsula Climate Response to Atmospheric Circulation Variability: Evidence for Contrasting Controls in Winter and Summer
Over the past 50 years the west coast of the Antarctic Peninsula has warmed more rapidly than any other region on Earth and the Peninsula as a whole has warmed faster than other regions of Antarctica. There have been significant changes in the regional cryosphere and ecosystems associated with this warming, most notably the rapid collapse of some of the ice shelves that used to border the Peninsula. Temperature records from Antarctic Peninsula climate stations were used together with atmospheric reanalyses to test the hypothesis that the regional warming is driven by atmospheric circulation changes. Winter temperatures, particularly along the southern parts of the west coast, are strongly correlated with the strength of the Pacific South American (PSA) teleconnection pattern, itself influenced by conditions in the tropical Pacific. By contrast, summer temperatures in the northern and eastern parts of the region are closely related to an index of the Southern Hemisphere Annular Mode (SAM), which is a measure of the strength of the circumpolar westerlies. Recent studies have demonstrated that there has been a positive trend in the SAM index (strengthening westerlies) over the past few decades, which is largely attributable to increases in greenhouse gases. The summer warming of the Peninsula is thus likely to have an anthropogenic component. However, attribution of winter temperature trends in the Peninsula remains problematical as the links between anthropogenic forcing and changes in the PSA pattern have not been well established.
GC44A-06 17:15h
Glaciers in Equilibrium - Results from the McMurdo Dry Valleys, Antarctica
Since 1993 the mass balance of two glaciers in the McMurdo Dry Valleys, Antarctica ($163\deg$E $77.5\deg$S) has been measured. The magnitude of annual mass gain or loss does not exceed 10 cm water equivalent averaged over each glacier, consistent with the local climate of a polar desert. The overall trend in mass balance shows that the glaciers are in approximate balance with the current climate and no obvious trends exist in either the winter or summer balances. These are similar to a set of mass balance measurements made in another part of the dry valleys during the 1970s (Chinn, 1985). Recent analysis of the climate of the dry valleys shows this region is cooling at a rate of $0.7\deg$C per decade during this period since 1986, which is reflected in the overall lowering of lake levels, decreased primary productivity of the lakes, and declining number of invertebrates (Doran et al., 2002). Although an unusually warm period occurred in the summer of 2001-2002, annual temperatures continue to cool. This region seems to be isolated from the warming elsewhere in Antarctica and the cooling in this part of the Ross Sea region may be due to El Nino forcing (Bertler et al, 2004). The sluggish behavior of the glaciers results from a low mass exchange and an apparent climatic buffering, which supports evidence from the geologic record that these glaciers have not advanced more than a few hundred meters over the past 3 million years (Hall et al., 1993). Many of the glaciers, however, are advancing which probably results from a slow time-scale response from warming conditions in the past millennium.
GC44A-07 17:30h
Long Term Decline in River Discharge in the Canadian Middle Arctic Recorded in Laminated Lake Sediments: a Hydrological Response to Global Warming?
Detailed sedimentological and diatom investigations were used to develop an understanding of the long term hydrological behaviour in the Lord Lindsay River on the central Boothia Peninsula, Nunavut, Canada (71dN, 95dW). This location was chosen to avoid geomorphic controls that could influence long term sediment availability and limit the interpretation of the sedimentary record. Additionally, two years of sediment delivery observations in the Lord Lindsay River and two major tributaries were carried out to support analysis of the sediments. Results indicate that sediment transport occurs dominantly during short period of peak discharge during the spring snowmelt period. Our monitoring indicates a broad proportional control over total sediment delivery by integrated catchment snow water equivalence. Summer rainfall events did not result in substantial additional sediment delivery. Analysis of the long varve record from Sanagak Lake indicates declining sedimentation since the 17th century, with the lowest levels in the 20th century. The decline since c. 1850 AD is coincident with a decrease in lotic (riverine) diatoms in the sedimentary record. Both records suggest that peak and overall discharge in the Lord Lindsay River have substantially declined. Comparison with long arctic proxy temperature records suggest a linkage between increased warmth and declining discharge intensity, potentially through increased snow sublimation and melt infiltration, or, a reduction in snow pack. While the mechanisms for the observed changes remain uncertain, our data are consistent with a hydrological response rather than a geomorphic change in sediment availability. Contrary to many glacierized catchments, the large rivers in this region appear to have been affected by a shift towards shorter or less intense nival discharge peaks.
GC44A-08 17:45h
Projected Impacts of Climate and UV Change on Arctic Freshwater Ecosystems
The Arctic Climate Impact Assessment (ACIA - http://www.acia.uaf.edu/), which will be released in winter 2004, is an international project of the Arctic Council and the International Arctic Science Committee (IASC), which evaluates and synthesizes knowledge on climate variability and change, increased ultraviolet radiation, and their impacts on northern landscapes, ecosystems and communities. Future changes in climate and UV in the Arctic are predicted to have far-reaching impacts on, and in some cases fundamentally alter, the hydrology and ecology of freshwater ecosystems. Key effects include alteration and loss of habitat for northern species as river flows change, lake and river ice conditions shift, and water levels respond to changes in temperature and precipitation, threatening the abundance and diversity of arctic species. Productivity and trophic interactions within these systems will change in response to increased nutrient, sediment and carbon loadings from increasingly vegetated, permafrost-degraded catchments. Shift of the geographic range of southerly species northward as new and altered freshwater habitats develop will be detrimental to arctic species and the northern populations that depend on them. These effects of climate change will be compounded by climate interactions with contaminants, and the potential for enhanced UV exposure. Climate interactions with arctic freshwater ecosystems will be complex and may be propagated through ecosystems in ways that are difficult to predict. As such, our understanding of the structure and function of arctic freshwater systems and their interrelationships with climate and other environmental variables must advance such that the accuracy of predictions and the effectiveness of adaptation and mitigation strategies increases. Steps towards this end include establishment of an integrated network of international, long-term freshwater monitoring and hydro-ecological research sites in the Arctic.