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FROM VOLUME 9, NUMBER 9, SEPTEMBER 1996

PROFESSIONAL PUBLICATIONS...
TREND ANALYSIS: TEMPERATURE

Item #d96sep47

Three related items in Clim. Change, 33(4), Aug. 1996:

"Examination of 'Global Atmospheric Temperature Monitoring with Satellite Microwave Measurements': 2. Analysis of Satellite Data," C. Prabhakara (Code 913, NASA-Goddard, Greenbelt MD 20771), J.-M. Yoo et al., 459-476. Satellite microwave measurements were used by Spencer and Christy (1992) to determine that the Earth exhibits no temperature trend in the period 1979-1990, in contrast to findings based on other types of data. This paper presents a method for estimating a possible bias in these measurements, finding it to be about 1 K across significant parts of the tropical ocean rain belts, a factor that could seriously affect a trend estimate.

"Analysis of [the previous paper]," R.W. Spencer (Global Hydrol. & Clim. Ctr., NASA Marshall Space Flight Ctr., Huntsville AL 35812), J.R. Christy, N.C. Grody, 477-489. Presents several lines of evidence to show that the previous paper overestimates contamination of satellite measurements by hydrometeors, and that the suggestion that long-term trend estimates are suspect is not supported by radiosonde data.

"Examination of 'Global Atmospheric ...(3) Cloud and Rain Contamination,'" C. Prabhakara (address above), M. Cadeddu et al., 491-496. A further analysis and response to Spencer et al., concluding that they underestimate the contamination by hydrometeors.

Item #d96sep48

"Climatic Trends from Isotopic Records of Tree Rings: The Past 100-200 Years," X. Feng (Dept. Earth Sci., Dartmouth College, Hanover NH 03755), S. Epstein, ibid., 551-562.

There has been much discussion about global warming from greenhouse gas accumulation in the atmosphere, but relatively little about spatial and temporal climatic variations that may be associated with a warmer climate or with anthropogenic activities. This article presents evidence that an increase in climatic variability may have started, based on trees sampled randomly around the world.

Item #d96sep49

"Robust Estimation of Background Noise and Signal Detection in Climatic Time Series," M.E. Mann (Dept. Geol. & Geophys., POB 208109, Yale Univ., New Haven CT 06520), J.M. Lees, ibid., 33(3), 409-445, July 1996.

Presents a new technique for isolating climate signals in time series characterized by a "red noise" spectrum generated by temporal persistence. Applies the technique to several historical and paleoclimatic time series. The historical global-average surface temperature record shows a highly significant warming trend, and weakly significant quasiperiodic signals within the ENSO frequency band.

Item #d96sep50

"The July 1995 Heat Wave in the Midwest: A Climatic Perspective and Critical Weather Factors," K.E. Kunkel (Midwest Clim. Ctr., Illinois State Water Survey, 2204 Griffith Dr., Champaign IL 61820), S.A. Chagnon et al., Bull. Amer. Meteor. Soc., 77(7), 1507-1518, July 1996.

Comparison with past heat waves shows that this was the most intense short-duration heat wave in at least the past 48 years at some locations in the region. In Chicago, where the majority of related fatalities occurred, its intensity was exceeded only by a few periods in the 1910s and 1930s. Impacts in the urban center were exacerbated by an urban heat island that raised nocturnal temperatures by more than 2° C.

Item #d96sep51

"Vertical Patterns of Free and Forced Climate Variations," K.Ya. Vinnikov (Dept. Meteor., Univ. Maryland, College Pk. MD 20742; e-mail: alan@atmos. umd.edu), A. Robock et al., Geophys. Res. Lett., 23(14), 1801-1804, July 1, 1996.

Observations of the vertical structure of the global atmosphere show that the lower atmosphere has warmed over the past three decades, while the upper layers have cooled. To determine whether these changes could be natural fluctuations, the vertical structure of fluctuations was analyzed in a 1000-year simulation of a coupled ocean-atmosphere-land model. The global mean temperatures of the upper and lower layers tended to fluctuate in the same manner, strengthening the argument that the observed changes of the past three decades can at least partly be attributed to anthropogenic activities.

Item #d96sep52

"Increased Activity of Northern Vegetation Inferred from Atmospheric CO₂ Measurements," C.D. Keeling (Scripps Inst. Oceanog., La Jolla CA 92093), J.F.S. Chin, T.P. Whorf, Nature, 382(6587), 146-149, July 11, 1996.

Monitoring shows that the annual amplitude of the seasonal cycle of atmospheric CO₂ has increased since the early 1960s by 20% in Hawaii and by 40% in the Arctic. In addition, there is evidence that the start of the growing season has lengthened by a week. The authors propose that the amplitude increases reflect increasing assimilation of CO₂ by land plants in response to climate changes accompanying recent rapid increases in temperature.

Item #d96sep53

"Global Surface Air Temperature in 1995: Return to Pre-Pinatubo Level," J. Hansen (NASA Goddard Inst. Space Studies, 2880 Broadway, New York NY 10025), R. Ruedy, M. Sato, Geophys. Res. Lett., 23(13), 1665-1668, June 15, 1996.

Updates a previous analysis with more recent data, and inclusion of marine temperatures. The global surface air temperature has increased about 0.5° C from the minimum of mid-1992, a year after the Mt. Pinatubo eruption. Since El Niño warming was small in 1995, the solar cycle was near a minimum, and ozone depletion was near record levels, the observed high temperature supports the contention of an underlying global warming trend. The pattern of Northern Hemisphere temperature change in recent decades appears to reflect a change of atmospheric dynamics; increasing greenhouse gases are postulated as a cause. The data set is available on the Internet: http://www.giss.nasa.gov/ Data/GISTEMP.

Item #d96sep54

"Analysis of Satellite-Based Estimates of Tropospheric Diurnal Temperature Range," R.C. Balling Jr. (Off. Climatol., Arizona State Univ., Tempe AZ 85287), J.R. Christy, J. Geophys. Res., 101(D8), 12,827-12,832, May 27, 1996.

A decrease in the diurnal temperature range has been identified throughout this century in many of the world's land-based climate records, but documentation of the seasonality, magnitude and geography of these changes has been hampered by the lack of globally homogeneous temperature measurements. This preliminary study uses satellite-based estimates of diurnal temperature range, finding that it is higher over land areas, high in summer and low in winter, and low in the winter season for the land areas between 30° N and 60° N.

Item #d96sep55

"Greenhouse Warming and Changes in the Seasonal Cycle of Temperature: Model versus Observations," M.E. Mann (Dept. Geol. & Geophys., POB 208109, Yale Univ., New Haven CT 06520), J. Park, Geophys. Res. Lett., 23(10), 1111-1114, May 15, 1996.

Thomson (1995) argues that an enhanced greenhouse effect may be altering the seasonal cycle in temperature. This study examines the amplitude and phase of the seasonal cycle in Northern Hemisphere observed temperatures, and compares them with the response of two climate models to increasing CO₂. Finds sizable amplitude decreases in both models and observations, but the phase responses differ greatly. The retreat of winter ice in high latitudes appears to explain the model's response to CO₂ increase.

Item #d96sep56

"Global Surface Temperatures," D.E. Parker (Hadley Ctr., Meteor. Off., London Rd., Bracknell, Berkshire RG12 2SY, UK), P.D. Jones, Nature, 381(6580), 270, May 23, 1996.

A reply countering several claims in the following comment by Gordon, which criticized a U.K. Met Office press release on 1995 global temperature.

Item #d96sep57

"Is Global Warming Climate Change?" A.H. Gordon (Inst. Atmos. & Marine Sci., Flinders Univ., Bedford Pk., 5042 S. Australia), J.A.T. Bye, R.A.D. Byron-Scott, ibid., 380(6574), 478, Apr. 11, 1996.

The U.K. Met Office press release that claimed 1995 was the warmest year so far failed to contain three important provisos. Moreover, the statistical concept of "bounded random walks," rather than any underlying trend, could account for the relatively large proportion of warm years recently.

Item #d96sep58

"Influence of Variations in Extratropical Wintertime Teleconnections on Northern Hemisphere Temperature," J.W. Hurrell (NCAR, POB 3000, Boulder CO 80307), Geophys. Res. Lett., 23(6), 665-668, Mar. 15, 1996.

Since the mid-1970s, Northern Hemisphere temperatures have increased. Recent warming has been largest during the winter and spring seasons over the mid-latitude continents, and the pattern of temperature change is related to decadal changes in the circulation of the atmosphere and oceans. This paper examines this relationship using multivariate linear regression. The changes in circulation since the mid-1970s, regardless of whether they were caused by greenhouse gas forcing or natural ocean-atmosphere fluctuations, have resulted in a surface temperature anomaly pattern that has amplified the hemispheric-averaged warming because of its interaction with land and ocean. Because anomalies over oceans are more subdued due to the large heat capacity of water, the hemispheric mean surface air temperature is largely determined by the temperature of the continents.

Item #d96sep59

"Major Optical Depth Perturbations to the Stratosphere from Volcanic Eruptions: Pyrheliometric Period, 1881-1960," R.B. Sothers (NASA Goddard Inst. Space Studies, 2880 Broadway, New York NY 10025), J. Geophys. Res., 101(D2), 3901-3920, Feb. 20, 1996.

A detailed chronology of major stratospheric dust veils has been constructed by searching the primary literature for relevant data of various kinds, especially pyrheliometry. During the long period 1881-1992, about 80% of all stratospheric aerosols generated by the largest sulfur-producing eruptions were injected during the two short time intervals 1883-1902 and 1982-1991. The long-term (1881-1992) average annual production rate of stratospheric SO2 from the largest eruptions was 0.8 Tg per year, about half the average rate since 1981. Implications are discussed.

Item #d96sep60

"Responses of Arctic Tundra to Experimental and Observed Changes in Climate," F.S. Chapin III (Dept. Integrative Biol., Univ. California, Berkeley CA 94720), G.R. Shaver et al., Ecology, 76(3), 694-711, 1995.

Light, temperature, and nutrients were manipulated in study plots. During the 9-year study, coinciding with the warmest decade on record in the region, biomass of one dominant tundra species unexpectedly changed in control plots in the direction predicted by these experiments and by Holocene pollen records. This suggests that regional climatic warming may already be altering the species composition of Alaskan Arctic tundra.