Identification of external influences on temperatures in California
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We use nine different observational datasets to estimate California-average temperature trends during the periods 1950–1999 and 1915–2000. Observed results are compared to trends from a suite of climate model simulations of natural internal climate variability. On the longer (86-year) timescale, increases in annual-mean surface temperature in all observational datasets are consistently distinguishable from climate noise. On the shorter (50-year) timescale, results are sensitive to the choice of observational dataset. For both timescales, the most robust results are large positive trends in mean and maximum daily temperatures in late winter/early spring, as well as increases in minimum daily temperatures from January to September. These trends are inconsistent with model-based estimates of natural internal climate variability, and thus require one or more external forcing agents to be explained. Observational datasets with adjustments for urbanization effects do not yield markedly different results from unadjusted data. Our findings suggest that the warming of Californian winters over the twentieth century is associated with human-induced changes in large-scale atmospheric circulation. We hypothesize that the lack of a detectable increase in summertime maximum temperature arises from a cooling associated with large-scale irrigation. This cooling may have, until now, counteracted summertime warming induced by increasing greenhouse gases effects.
KeywordsDiurnal Temperature Range Observational Dataset National Climatic Data Center Climate Noise Nighttime Warming
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- Bereket L, Fabris D, Gonzalez JE, Chiappari S, Zarantonello S, Miller NL, Bornstein R (2005) Urban heat islands in California’s Central Valley. Bull Am Meteorol Soc 86:1542–1543Google Scholar
- Karl TR, Williams CN Jr, Quinlan FT (1990) U.S. Historical Climatology Network (HCN) Serial Temperature and Precipitation Data. ORNL/CDIAC-30, NDP-019/R1. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, TennesseeGoogle Scholar
- Karoly DJ, Wu Q (2005) Detection of regional surface temperature trends. J Clim 18:4337–4343Google Scholar
- Kueppers LM, Snyder MA, Sloan LC, Cayan D, Jin J, Kanamaru H, Kanamitsu M, Miller NL, Tyree M, Du H, Weare B (2007) Seasonal temperature responses to land-use change in the western United States. Glob Planet Change (in press)Google Scholar
- Mitchell JFB, Karoly DJ, Hegerl GC, Zwiers FW, Allen MR, Marengo J (2001) Detection of climate change and attribution of causes. In: Houghton JT et al. (eds) Climate Change 2001: The Scientific Basis, Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, pp. 695–738Google Scholar
- Mitchell TD, Carter TR, Jones PD, Hulme M, New M (2004) A comprehensive set of high-resolution grids of monthly climate for Europe and the globe: the observed record (1901–2000) and 16 scenarios (2001–2100). Tyndall Working Paper 55, Tyndall Centre, UEA, Norwich. UK. http://www.tyndall.ac.uk/
- Santer BD, Wigley TML, Gleckler PJ, Bonfils C, Wehner MF, AchutaRao K, Barnett TP, Boyle JS, Bruggemann W, Fiorino M, Gillett N, Hansen JE, Jones PD, Klein SA, Meehl GA, Raper SCB, Reynolds RW, Taylor KE, Washington WM (2006) Causes of ocean surface temperature changes in Atlantic and Pacific hurricane formation regions. Proc Natl Acad Sci U S A 103:13905–13910CrossRefGoogle Scholar
- Willmott CJ, Matsuura K (1998) Global air temperature and precipitation: regridded monthly and annual climatologies (version 2.01), Newark, Delaware: Center for Climatic Research. Dept. of Geography, Univ. of DelawareGoogle Scholar