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P. D. Jones
,
T. M. L. Wigley
, and
P. M. Kelly

Abstract

We have produced, using objective techniques, a long-term series of average Northern Hemisphere temperatures based on monthly mean station data gridded on a 5° latitude by 10° longitude grid. Difficulties in the estimation of this parameter are discussed, deficiencies in the currently available data base and possible effects on the estimated average are described, and monthly mean data are presented. Long-term trends and extremes are identified in the annual and seasonal data. All seasons show similar long-term trends, but there are noticeable differences on time scales of 10 years and less. For example, for winter temperature, the early 20th century warming peaked during the 1940's whereas the maximum in the other seasons was in the previous decade. Both the magnitude of the long-term trends and the year-to-year variability has been greatest in winter. There is evidence that the long-term cooling that characterized the 1940's, 1950's and 1960's has ended. Warming began in the mid to late 1960's in winter and spring, in the mid 1970's in autumn and later in summer. Year-to-year variability has been particularly pronounced during the 1970's. For example, 1972 was the coldest winter since 1918, yet 1980 and 1981 were among the five warmest winters during the last 100 years. There is, as yet, no statistical reason to associate the recent warming with atmospheric CO2 increases.

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S. C. B. Raper
,
T. M. L. Wigley
,
P. R. Mayes
,
P. D. Jones
, and
M. J. Salinger

Abstract

Antarctic temperature variations for 1957°82 have been objectively analyzed by gridding monthly data, from 16 stations, onto a 5° latitude by 10° longitude grid, from 65 to 90°S. These gridded data were used to calculate monthly values of the spatial mean temperature south of 65°S. The uncertainty in the area average is estimated to be 0.22°C for the annual values prior to 1970. After 1970 there is an additional uncertainty of about 0.10−0.16°C due to the cessation of Byrd station. The annual mean and summer areas averages show significant linear warming trends amounting to 0.74 and 0.77°C respectively. Spatial characteristics of the annual and seasonal temperature variations are described using principal components analysis of the station anomaly data. The first two principal components of the annual and winter data are similar PC1-winter is also similar to the winter pattern for linen trend found by van Loon and Williams for 1956–73. The warming trend associated with this pattern ceased in the mid-1970s.

Relationships between Antarctic temperatures and various parameters are investigated using linear trend and correlation analyses. Antarctic temperatures cannot be inferred from the long Orcadas record and the relationships between Antarctic temperatures and sea ice extent are complex. The most significant correlations between mean Antarctic temperature and sea ice extent averaged around Antarctica am found in spring; warm springs tend to be associated with anomalously large maximum sea ice extent. Lower Antarctic temperatures occur during summers and winters with strong westerlies (significant at the 0.1% level in summer and at the 0.1% level in winter).

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