Harris: The recent work by Professor Elizabeth Barnes of Colorado State has shown that there were methodological deficiencies in the research suggesting increased jet undulations with global warming. And that there is no observational evidence of increased waviness. Furthermore, there is little evidence that the jet approaching North America has weakened recently. The IPCC, the global group of scientists that have come together to estimate the impacts of increased greenhouse gases, have been clear about their conclusions: “There is likely to be a decline in the frequency of cold air outbreaks (i.e., periods of extreme cold lasting from several days to over a week) in NH winter in most areas.”
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Just to illustrate that extremes are NOT increasing in the U.S., NOAA maintains a Climate Extreme Index (CEI) that includes many parameters. Here is a plot of that index for winter for the last century for North America. No trend.
