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Judith Curry: U.S. National Climate Assessment Report

Judith Curry, Climate Etc.

My main conclusion from reading the U.S. National Climate Assessment Report is this: the phrase ‘climate change’ is now officially meaningless.

The report effectively implies that there is no climate change other than what is caused by humans, and that extreme weather events are equivalent to climate change.  Any increase in adverse impacts from extreme weather events or sea level rise is caused by humans. Possible scenarios of future climate change depend only on emissions scenarios that are translated into warming by climate models that produce far more warming than has recently been observed.

Some of the basic underlying climate science and impacts reported is contradictory to the recent IPCC AR5 reports.  Pat Michaels and Chip Knappenberger have written a 134 page critique of a draft of the NCADAC report [link].

Even in the efforts to spin extreme weather events as alarming and caused by humans, Roger Pielke Jr. has tweeted the following quotes from the Report:

  • “There has been no universal trend in the overall extent of drought across the continental U.S. since 1900″
  •  “Other trends in severe storms, including the intensity & frequency of tornadoes, hail, and damaging thunderstorm winds, are uncertain”
  • “lack of any clear trend in landfall frequency along the U.S. eastern and Gulf coasts”
  • “when averaging over the entire contiguous U.S., there is no overall trend in flood magnitudes”

As a I wrote in a previous post on a draft of the report, the focus should be on the final Chapter 29: Research Agenda, which outlines what we DON’T know.  Chapter 28 Adaptation is also pretty good.  Chapter 27 Mitigation is also not bad, and can hardly be said to make a strong case for mitigation.  Chapter 26 on Decision Support is also ok, with one exception: they assume the only scenarios of future climate are tied to CO2 emissions scenarios.

An interesting feature of the report is Traceable Accounts – for each major conclusion a Traceable Account is given that describes the Key Message Process, Description of evidence base, New information and remaining uncertainties, Assessment of confidence based on evidence.  The entertainment value comes in reading the description of very substantial uncertainties, and then seeing ‘very high confidence’.  This exercise, while in principle is a good one, in practice only serves to highlight the absurdity of the ‘very high confidence’ levels in this report.

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