Alexander, L.V., Zhang, X., Peterson, T.C., Caesar, J., Gleason, B., Klein Tank, A.M.G., Haylock, M., Collins, D., Trewin, B., Rahimzadeh, F., Tagipour, A., Rupa Kumar, K., Revadekar, J., Griffiths, G., Vincent, L., Stephenson, D.B., Burn, J., Aguilar, E., Brunet, M., Taylor, M., New, M., Zhai, P., Rusticucci, M. and Vazquez-Aguirre, J.L. 2006. Global observed changes in daily climate extremes of temperature and precipitation. Journal of Geophysical Research 111: 10.1029/2005JD006290.
What was done
The authors developed what they call "the most up-to-date and comprehensive global picture of trends in extreme temperature," using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists from around the world, after which several seasonal and annual temperature indices for the period 1951-2003 were calculated and gridded, and trends in the gridded fields were computed and tested for statistical significance.
What was learned
Alexander et al. report that "over 70% of the land area sampled showed a significant increase in the annual occurrence of warm nights while the occurrence of cold nights showed a similar proportion of significant decrease," with some regions experiencing "a more than doubling of these indices." For the majority of the other temperature indices, however, they found that only 20% of the land area sampled exhibited statistically significant changes, specifically noting that "maximum temperature extremes have also increased but to a lesser degree."
What it means
The two dozen researchers state that their results "agree with earlier global studies (e.g., Jones et al., 1999) and regional studies (e.g., Klein Tank and Konnen, 2003; Manton et al., 2001; Vincent and Mekis, 2006; Yan et al., 2002), which imply that rather than viewing the world as getting hotter it might be more accurate to view it as getting less cold." Such is truly the case; and such a result does not sound all that bad.
Klein Tank, A.M.G. and Konnen, G.P. 2003. Trends in indices of daily temperature and precipitation extremes in Europe, 1946-99. Journal of Climate 16: 3665-3680.
Manton, M.J., Della-Marta, P.M., Haylock, M.R., Hennessy, K.J., Nicholls, N., Chambers, L.E., Collins, D.A., Daw, G., Finet, A., Gunawan, D., Inape, K., Isobe, H., Kestin, T.S., Lefale, P., Leyu, C.H. Lwin, T., Maitrepierre, L., Ouprasitwong, N., Page, C.M., Pahalad, J., Plummer, N., Salinger, M.J., Suppiah, R., Tran, V.L., Trewin, B., Tibig, I. and Yee, D. 2001. Trends in extreme daily rainfall and temperature in southeast Asia and the South Pacific: 1916-1998. International Journal of Climatology 21: 269-284.
Vincent, L.A. and Mekis, E. 2006. Changes in daily and extreme temperature and precipitation indices for Canada over the 20th century. Atmosphere and Ocean, in press.
Yan, Z., Jones, P.D., Davies, T.D., Moberg, A., Bergstrom, H., Camuffo, D., Cocheo, C., Maugeri, M., Demaree, G.R., Verhoeve, T., Thoen, E., Barriendos, M., Rodriguez, R., Martin-Vide, J. and Yang, C. 2002. Trends of extreme temperatures in Europe and China based on daily observations. Climatic Change 53: 355-392.Reviewed 14 June 2006