CLIMATOLOGY

Extreme Weather

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Science  25 Aug 2000:
Vol. 289, Issue 5483, pp. 1257
DOI: 10.1126/science.289.5483.1257a

Instrumental records show that global average annual surface temperatures increased by about 0.5 °C over the course of the twentieth century. Climate change is a more complex phenomenon than can be illustrated by this one number, however, and it is of importance to quantitate how other aspects of climate have varied.

Easterling et al. describe the existing evidence for changes in several of these properties—daily maximum and minimum temperatures, glacial and snow cover, precipitation, cloudiness, and soil moisture—in an attempt to construct a more comprehensive picture of global climate change. They use these data to address three fundamental, yet vexing questions: Is the planet getting warmer? Is the hydrologic cycle changing? Are weather and climate becoming more extreme or variable? The short answer to all of these questions, taking into account an admittedly incomplete data set, is “yes.” More detailed analyses of existing data, performed with due caution regarding possible systematic biases and uncertainties, are needed. — HJS

J. Geophys. Res. Atmos.105, 20101 (2000).

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