Roger G. Barry

OBSERVATIONAL EVIDENCE OF RECENT CHANGE IN THE NORTHERN HIGH-LATITUDE ENVIRONMENT

Studies from a variety of disciplines documentrecentchange in the northern high-latitude environment.Prompted by predictions of an amplified response oftheArctic to enhanced greenhouse forcing, we present asynthesis of these observations. Pronounced winter andspring warming over northern continents since about 1970ispartly compensated by cooling over the northern NorthAtlantic. Warming is also evident over the centralArcticOcean. There is a downward tendency in sea ice extent,attended by warming and increased areal extent of theArctic Oceans Atlantic layer. Negative snow coveranomalies have dominated over both continents sincethelate 1980s and terrestrial precipitation has increasedsince 1900. Small Arctic glaciers have exhibitedgenerally negative mass balances. While permafrost haswarmed in Alaska and Russia, it has cooled in easternCanada. There is evidence of increased plant growth,attended by greater shrub abundance and northwardmigration of the tree line. Evidence also suggeststhatthe tundra has changed from a net sink to a net sourceofatmospheric carbon dioxide.Taken together, these results paint a reasonablycoherent picture of change, but their interpretationassignals of enhanced greenhouse warming is open todebate.Many of the environmental records are either short,areof uncertain quality, or provide limited spatialcoverage. The recent high-latitude warming is also nolarger than the interdecadal temperature range duringthis century. Nevertheless, the general patterns ofchange broadly agree with model predictions. Roughlyhalfof the pronounced recent rise in Northern Hemispherewinter temperatures reflects shifts in atmosphericcirculation. However, such changes are notinconsistentwith anthropogenic forcing and include generallypositive phases of the North Atlantic and ArcticOscillations and extratropical responses to theEl-NiñoSouthern Oscillation. An anthropogenic effect is alsosuggested from interpretation of the paleoclimaterecord,which indicates that the 20th century Arctic is thewarmest of the past 400 years.

Icelandic Low Cyclone Activity: Climatological Features, Linkages with the NAO, and Relationships with Recent Changes in the Northern Hemisphere Circulation

Abstract Output from a cyclone detection and tracking algorithm, applied to twice-daily sea level pressure (SLP) fields for the period 1966–93, is used to examine the characteristics of cyclone activity associated with the locus of the mean Icelandic low (IL), variability during extremes of the North Atlantic oscillation (NAO), and recent changes in relation to circulation over the Northern Hemisphere. Cyclone events within the climatological IL display a modest seasonal cycle with a winter maximum. However, winter systems are considerably deeper than their summer counterparts with much larger maximum deepening rates. During the cold season (October–March), IL cyclone intensities are typical of oceanic systems but exhibit lower maximum deepening rates. During the warm season (April–September), intensities are typical of Northern Hemisphere values with deepening characteristics similar to those for all extratropical oceans. Depending on the month, 10%–15% (13%–18%) of cyclone events in the IL region repres...

Statistics and characteristics of permafrost and ground-ice distribution in the Northern Hemisphere

Abstract The recently published digital version of the International Permafrost Association (IPA) Circum-Arctic Map of Permafrost and Ground Ice Conditions (the IPA map), together with ancillary data sets of the global land cover characteristics data base and the Global Land One-kilometer Base Elevation data base, are used to investigate the distribution of permafrost and ground ice in the Northern Hemisphere. Our study indicates that permafrost underlies approximately 22.79×106 km2 or 23.9% of the exposed land area of the Northern Hemisphere. Permafrost extends from 26°N in the Himalayas to 84°N in northern Greenland. Approximately 70% of the permafrost is distributed between 45 and 67°N. Generally, permafrost with high ice content (>20% by volume) and relatively thick overburden cover (>5 to 10 m) is found at high latitudes, representing approximately 8.57% of the total permafrost area, or 2.02% of the exposed land area of the Northern Hemisphere. Permafrost with low ice content (<10% by volume with either thick or thin overburden cover) occurs mainly in mountainous regions and high plateaus, representing approximately 66.5% of the total permafrost area or 15.8% of the exposed land area. Approximately 62% of the permafrost of the Northern Hemisphere is found below 500 m a.s.l. and about 10% occurs above 3000 m a.s.l. Based on the IPA map categories, the estimated volume of ground ice in the Northern Hemisphere is between 5.63 and 15.12×103 km3, corresponding to ∼2–4 cm sea level equivalent. Based on alternative assumptions, the volume of ground ice may be between 11.37 and 36.55×103 km3, which corresponds to 3-10 cm sea-level equivalent.

A record minimum arctic sea ice extent and area in 2002

[1] Arctic sea ice extent and area in September 2002 reached their lowest levels recorded since 1978. These conditions likely resulted from (1) anomalous warm southerly winds in spring, advecting ice poleward from the Siberian coast (2) persistent low pressure and high temperatures over the Arctic Ocean in summer, promoting ice divergence and rapid melt.

Recent decreases in Arctic summer ice cover and linkages to atmospheric circulation anomalies

Sea ice data from November 1978 through September 1995 for the Arctic Ocean and peripheral seas indicate that summer ice coverage has been below normal in recent years, with extreme minima in 1990, 1993, and 1995. The net trend in summer ice cover over the 17-year period is −0.6% per year, with the extent of the perennial ice pack reduced by 9% in 1990–1995 compared with 1979–1989. The reductions are greatest in the Siberian sector of the Arctic Ocean. Linkages are proposed between these ice anomalies and a sharp increase since 1989 in the frequency of low pressure systems over the central Arctic.

The status of research on glaciers and global glacier recession: a review

Mountain glaciers are key indicators of climate change, although the climatic variables involved differ regionally and temporally. Nevertheless, there has been substantial glacier retreat since the Little Ice Age and this has accelerated over the last two to three decades. Documenting these changes is hampered by the paucity of observational data. This review outlines the measurements that are available, new techniques that incorporate remotely sensed data, and major findings around the world. The focus is on changes in glacier area, rather than estimates of mass balance and volume changes that address the role of glacier melt in global sea-level rise. The glacier observations needed for global climate monitoring are also outlined.

Characteristics of Arctic synoptic activity, 1952–1989

SummarySynoptic activity for the Arctic is examined for the period 1952–1989 using the National Meteorological Center sea level pressure data set. Winter cyclone activity is most common near Iceland, between Svalbard and Scandinavia, the Norwegian and Kara seas, Baffin Bay and the eastern Canadian Arctic Archipelago; the strongest systems are found in the Iceland and Norwegian seas. Mean cyclone tracks, prepared for 1975–1989, confirm that winter cyclones most frequently enter the Arctic from the Norwegian and Barents seas. Winter anticyclones are most frequent and strongest over Siberia and Alaska/Yukon, with additional frequency maxima of weaker systems found over the central Arctic Ocean and Greenland.During summer, cyclonic activity remains common in the same regions as observed for winter, but increases over Siberia, the Canadian Arctic Archipelago and the Central Aretic, related to cyclogenesis over northern parts of Eurasia and North America. Eurasian cyclones tend to enter the Aretic Ocean from the Laptev Sea eastward to the Chukchi Sea, augmenting the influx of systems from the Norwegian and Barents seas. The Siberian and Alaska/Yukon anticyclone centers disappear, with anticyclone maxima forming over the Kara, Laptev, East Siberian and Beaufort seas, and southeastward across Canada. Summer cyclones and anticyclones exhibit little regional variability in mean central pressure, and are typically 5–10 mb weaker than their winter counterparts.North of 65°N, cyclone and anticyclone activity peaks curing summer, and is at a minimum during winter. Trends in cyclone and anticyclone activity north of 65°N are examined through least squares regression. Since 1952, significant positive trends are found for cyclone numbers during winter, spring and summer, and for anticyclone numbers during spring, summer and autumn.

A CLIMATOLOGICAL TRANSECT ON THE EAST SLOPE OF THE FRONT RANGE, COLORADO

Climatological data collected from 1952 to 1970 at four ridge sites on the east slope of the Front Range, west of Boulder, Colorado, at elevations between 2,195 m and 3,750 m are analyzed using the TAXIR data retrieval system. Significant results of the climatography include the demonstration of a much greater mean annual precipitation at the two upper stations than previously reported. The mean total exceeds 100 cm at 3,750 m. Solar radiation totals show little or no change with elevation between 2,590 and 3,750 m for the annual average. Extremes of minimum air temperature for October 1969 at the two lower stations lay outside the theoretically expected 100-year return period for these stations. Daily precipitation and maximum and minimum temperatures are analyzed in terms of 700-mb circulation types in mid-season months, 1952 to 1970. Precipitation data are also examined with respect to 700mb wind velocity over Denver. The paper concludes with some recommendations for -further studies.

Freeze-up and Break-up of Lakes as an Index of Temperature Changes during the Transition Seasons: A Case Study for Finland

Abstract The statistical relationships between lake freeze-up/lake ice break-up dates and air temperature means over various time periods are analyzed for 63 lakes in Finland. Mean temperatures for the individual months before the lake event dates are strongly correlated with these dates; significant correlations hold for periods up to five months in length before freeze-up. Regression coefficients depend on location, but are consistent within regions. Latitude and distance from the coast are the most important sources of variation in the regression coefficients. The regression coefficients are used to translate changes in lake freeze-up/break-up dates into estimated changes in air temperature. In southern Finland a five day change in freeze-up date would represent a 1.1°C change in November temperature of the same sign. A time series of November temperatures estimated from lake freeze-up dates is derived and compared with observations at Helsinki. The spatial pattern of temperature change over time is al...

The Arctic Sea Ice‐Climate System: Observations and modeling

Significant advances are being made in our understanding of the Arctic sea ice-climate system. The mean circulation of the Arctic sea ice cover is now well defined through analysis of data from drifting stations and buoys. Analysis of nearly 20 years of daily satellite data from optical, infrared, and passive microwave sensors has documented the regional variability in monthly ice extent, concentration, and surface albedo. Advances in modeling include better treatments of sea ice dynamics and thermodynamics, improved atmosphere-ice-ocean coupling, and the development of high resolution regional models. Diagnostic studies of monthly and interannual sea ice variability have benefited from better sea ice data and geostrophic wind analyses that incorporate drifting buoy data. Some evidence exists for a small retreat of Arctic sea ice over the last 2 decades, but there are large decadal fluctuations in regional ice extent. Antiphase relationships between ice anomalies in different sectors can be related to changes in atmospheric circulation. Evidence suggests that episodes of significant salinity reduction in the North Atlantic, associated with extensive sea ice in the Greenland Sea, may be a manifestation of a decadal oscillation in the Arctic climate system. Aspects of the Arctic system in need of further attention include the surface energy budget and its variability, particularly with respect to the roles of cloud cover and surface types in summer. Sea ice thickness distribution data remain meager, and there are many unknowns regarding the circulation and hydrologic cycle of the Arctic Ocean and its links to the world ocean. Planned measurements from a new generation of satellites, supported by field programs, will provide much needed data to address these issues.