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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 9, NUMBER 1, JANUARY 1996

PROFESSIONAL PUBLICATIONS...
TREND ANALYSIS

Item #d96jan29

"The 1990-1995 El Niño-Southern Oscillation Event: Longest on Record," K.E. Trenberth (Clim. & Global Dynamics Div., NCAR, POB 3000, Boulder CO 80307), T.J. Hoar, Geophys. Res. Lett., 23(1), 57-60, Jan. 1, 1996.

Statistical analysis of the 113-year record of tropical Pacific data shows that both the recent trend for more ENSO events since 1976 and the prolonged 1990-1995 ENSO event are unexpected. This opens the possibility that the ENSO changes may be partly caused by the observed increase in greenhouse gases.

Item #d96jan30

"Recent Climatic Change in the World's Drylands," M. Hulme (Clim. Res. Unit, Univ. E. Anglia, Norwich NR4 7TJ, UK), ibid., 61-64.

Precipitation and temperature trends in nine dryland regions are analyzed for the period 1900 to 1994. No widespread desiccation in dryland climates is found, the African Sahel being the only region to demonstrate a significant drying trend. However all dryland regions have warmed, with the majority of the warming probably being unrelated to regional dryland effects.

Item #d96jan31

"The Elastic Response of the Earth to Interannual Variations in Antarctic Precipitation," C.P. Conrad (Dept. Earth, Atmos. & Planetary Sci., Mass. Inst. Technol., Cambridge MA 02139), ibid., 22(23), 3183-3186, Dec. 1, 1995.

Performs numerical experiments which show that the accumulation of ice mass in Antarctica is a highly variable process and can cause large variations in both sea level rise and in the Earth's elastic response to mass accumulation. If climate change significantly accelerates mass changes on the large ice sheets, these long-term trends could be detected in a few years by crustal displacement measurements.

Item #d96jan32

"Twentieth-Century Variability in Snow-Cover Conditions and Approaches to Detecting and Monitoring Changes: Status and Prospects," R.G. Barry (NSIDC/CIRES, Univ. Colorado, Boulder CO 80309), J.-M. Fallot, R.L. Armstrong, Prog. in Phys. Geog., 19(4), 520-532, Dec. 1995.

This review discusses which indices are the most suitable for detecting trends in snow cover, and illustrates the use of passive microwave data for the continental and regional scales. Data availability is also reviewed, and newly available records for the former USSR discussed. Summarizes model projections of changes in snow cover in several mountain regions that may result from greenhouse warming.

Item #d96jan33

"Dynamic Contribution to Hemispheric Mean Temperature Trends," J.M. Wallace (Dept. Atmos. Sci., AK-40, Univ. Washington, Seattle WA 98195), Y. Zhang, J.A. Renwick, Science, 270(5237), 780-783, Nov. 3, 1995.

A statistical study performed on Northern Hemisphere surface air temperatures, for the period 1900 through 1990, relates to the identification of a greenhouse "fingerprint" as predicted by climate models. Much of the temporal variability of monthly, hemispheric mean temperature anomalies is related to the amplitude of a distinctive spatial pattern of cold oceans and warm continents. The authors argue that the variability associated with this pattern is dynamically induced by the movement of warm and cold air masses, and is not necessarily an integral part of the fingerprint of global warming. However, the amplitude of the pattern increases between 1975 and 1990, and since it does contain elements of the greenhouse warming fingerprint, it is not clear whether greenhouse warming is a factor in this recent trend.

Item #d96jan34

"Atmospheric Methane at Mauna Loa and Barrow Observatories: Presentation and Analysis of in situ Measurements," E.J. Dlugokencky (CMDL, NOAA, 325 Broadway, Boulder CO 80303), L.P. Steele et al., J. Geophys. Res., 100(D11), 23,103-23,113, Nov. 20, 1995.

Describes several semi-continuous, in situ measurements made between 1986 and 1994, and examines features of the records ranging from the diurnal cycle to seasonal cycles and trends. The semi-continuous nature of the records are necessary for understanding implications concerning methane sources and sinks. The average trend at Mauna Loa was 9.7 ppb per year, decreasing at a rate of 1.5 ppb per year; the trend at Barrow was 8.5 ppb per year, decreasing at 2.1 ppb per year.

Item #d96jan35

"Increase in the Atmospheric Nitrous Oxide Concentration During the Last 250 Years," T. Machida (Natl. Inst. Environ. Studies, 16-2 Onogawa, Tsukuba 305, Japan), T. Nakazawa et al., Geophys. Res. Lett., 22(21), 2921-2924, Nov. 1, 1995.

Analysis of air samples extracted from an Antarctic ice core yielded a time history of N₂O with a precision of ±2 ppbv that is clearly less scattered than previous analyses. Concentrations of N₂O averaged about 276 ppbv in the 18th century, began to increase in the mid-19th century and reached 293 ppbv around 1965. The trend, believed to be anthropogenic, is compared with results of other studies.

Item #d96jan36

"Evaporation Losing Its Strength," T.C. Peterson (NCDC, NOAA, Asheville NC 28801), V.S. Golubev, P. Ya. Groisman, Nature, 377(6551), 687-688, Oct. 26, 1995.

Brief correspondence reporting a downward trend in evaporation of water as measured in pan evaporimeters in the U.S. and the former Soviet Union (FSU). Results imply that for large regions of the globe, the terrestrial evaporation component of the hydrological cycle has been decreasing, and provide a partial explanation for observed increases in runoff over the past two decades in the European part of the FSU and the northern U.S. Results are also consistent with speculation by Karl et al. that increased cloud cover may explain observed decreases in daily temperature range.

Item #d96jan37

"Trends in Air Temperature and Precipitation for Canada and Northeastern USA," T.Y. Gan (Dept. Civil Eng., Univ. Alberta, Edmonton AB T6G 2G7, Can.), Intl. J. Climatol., 15(10), 1115-1134, Oct. 1995.

Reports on an extensive statistical analysis of regional trends over the period 1949-1989 based on carefully selected station records. Western Canada has experienced significant warming in January and March, and to a limited extent in April, May, and June, but no trend or some cooling was found in eastern Canada and the northeastern U.S. No significant trend appeared in the precipitation record.

Item #d96jan38

"Testing for Change in the Frequency of El Niño Events," A.R. Solow (Woods Hole Oceanog. Inst., Woods Hole MA 02543), J. Clim., 8(10), 2563-2566, Oct. 1995.

Analysis of the El Niño record over the period 1525-1987 shows an apparent increase in frequency, but it is consistent with an overall increase in the completeness of the historical record. When the analysis is repeated for the later part of the period and for strong events alone, no trend is found.

Item #d96jan39

"Variations and Change in South American Streamflow," J.A. Marengo (CPTEC, INPE, Rod. Presidente Dutra Km. 40, 12630-000 Cachoeira Paulista, Sao Paulo, Brazil), Clim. Change, 31(1), 99-117, Sep. 1995.

Statistical analysis of long-term records of streamflow and rainfall in large portions of South America show no clear evidence of trend or change in the mean streamflow resulting from a climate change, even though significant trends toward drier conditions have been found for rivers in parts of Peru and Brazil. The effects of Amazon deforestation are not noticeable on the 1903-1992 interannual variability of the Rio Negro time series at Manaus nor in rainfall data.

Item #d96jan40

"Greenland Ice Sheet Thickness Changes Measured by Laser Altimetry," W. Krabill (Lab. Hydrospheric Proc., NASA Wallops Flight Facility, Wallops Is. VA 23337), Geophys. Res. Lett., 22(17), 2341-2344, Sep. 1, 1995.

Airborne laser-altimetry surveys that began in 1980 provide an indication of ice-thickness changes across southern Greenland in unprecedented detail, and show a thickening in western Greenland of up to two meters between 1980 and 1993. It is not yet possible to say whether this increase represents a long-term trend, or the cumulative effect of interannual variability of snow-accumulation rates.

Item #d96jan41

"Ocean Variability and Its Influence on the Detectability of Greenhouse Warming Signals," B.D. Santer (Lawrence-Livermore Natl. Lab., POB 808, Livermore CA 94550), U. Mikolajewicz et al., J. Geophys. Res., 100(C6), 10,693-10,725, June 15, 1995.

Describes extensive analyses of output from the Max Plank Institute's coupled ocean-atmosphere GCM that are intended to estimate when detectable greenhouse warming signals might be observed in the ocean. Explores sources of uncertainty related to the natural variability or noise, and sources inherent in any time-evolving signals. By using multiple indicators of change and statistical manipulation of data to reduce the signal-to-noise ratio, detection time can be reduced to 10-45 years.

Item #d96jan42

"Temperature Histories from Tree Rings and Corals," E.R. Cook (Tree Ring Lab., Lamont-Doherty Earth Observ., Rte. 9W, Palisades NY 10964), Clim. Dynamics, 11(4), 211-222, May 1995.

Recent temperature trends in long tree-ring and coral proxy temperature histories from around the world are examined to objectively determine how anomalous twentieth century temperature changes have been. Overall, the regional temperature histories support the larger-scale evidence for anomalous twentieth century warming based on instrumental records, but this warming cannot be confirmed as unprecedented in all regions.

Item #d96jan43

"A Note on the Recent Increase of Solar UV-B Radiation over Northern Middle Latitudes," C.S. Zerefos (Lab. Atmos. Phys., Aristotle Univ., Thessaloniki, Greece), A.F. Bais et al., Geophys. Res. Lett., 22(10), 1245-1247, May 15, 1995.

Three years of measurements at 40° N support earlier findings of increased solar UV-B irradiances under all-skies conditions associated with observed ozone decline during the period.

Item #d96jan44

"Changes in Winter Air Temperatures Near Lake Michigan, 1851-1993, as Determined from Regional Lake-Ice Records," R.A. Assel (Great Lakes ERL, NOAA, 2205 Commonwealth Blvd., Ann Arbor MI 48105), D.M. Robertson, Limnol. Oceanog., 40(1), 165-176, Jan. 1995.

Used data from two locations in Michigan and Wisconsin that have among the longest ice records available near the Great Lakes. Freeze-up and breakup dates were translated into changes in air temperature using empirical and process-driven models. Deduced temperatures show a 1.0-1.5° C increase in late winter and early spring about 1890, additional warming of 1.2° C in March since about 1940, and a warming of 1.1° C in January-March since about 1980. Ice records will continue to provide an indication of anticipated climatic warming, not only because of the large response of ice cover to small changes in air temperature, but also because these records integrate climatic conditions during the winter-spring seasons, when most warming is forecast to occur.

Item #d96jan45

"Study of Linear Trends of Time Series of Solar Radiation," Yu. V. Zhitorchuk (Voeykov Main Geophys. Observatory, Russia), Atmos. & Oceanic Phys., 30(3), 368-374, Dec. 1994. English edition.

Presents statistical analysis of data from 160 actinometric stations in the CIS, Baltic and Transcaucasian regions, from 1960 to 1987. Over most of the territory there was a significant per decade decrease in direct and global solar radiation of -6.3% and -2.5%, respectively. Suggests that the drop in global radiation is a manifestation of a negative cloud `feedback which helps offset the rise in air temperature caused by the greenhouse effect.