Trends in Climatic Data
Wednesday, September 7, 2011 - 11:30am - 12:10pm
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change reported that “warming of the climate system is unequivocal” and also that it is “very likely” (probability greater than ninety percent) that “most of the observed warming is due to the observed increase in anthropogenic greenhouse gas concentrations.” The choice of wording implies not only the existence of a statistically significant trend in temperature averages, but also that it is possible to distinguish between trends due to greenhouse gases and those due to other causes, including natural variation. In this talk, I shall describe some of the statistical methods that have been used to justify such statements. Some key points include determining the statistical significance of trends in time series subject to various kinds of autocorrelation assumptions, comparisons between trends in observed data and in climate models, and extensions from temperature averages to other forms of meteorological data, such a extreme precipitation or counts of tropical cyclones, where the statistical conclusions are not so clear-cut.