The Muddled Models of the IPCC

Key IPCC quotes

The fifth and latest IPCC assessment report, published in 2013, showed that climate models failed to predict the absence of warming from 1998 and 2012, and that climate scientists have no clear idea of why they failed. (NB. I have added the bolding in the following extracts.)

  1. “… the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to 0.15] °C per decade) … is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade).” [WG I SPM, page 5, section B.1, bullet point 3, and in full Synthesis Report on page SYR-6]
  2. “… an analysis of the full suite of CMIP5 historical simulations (…) reveals that 111 out of 114 realisations show a GMST trend over 1998–2012 that is higher than the entire HadCRUT4 trend ensemble ….” [WGI contribution, chapter 9, text box 9.2, page 769, and in full Synthesis Report on page SYR-8]
  3. “There may also be a contribution from forcing inadequacies and, in some models, an overestimate of the response to increasing greenhouse gas and other anthropogenic forcing (dominated by the effects of aerosols).” [WG I SPM, section D.1, page 15, bullet point 2, and full Synthesis Report on page SYR-8]
  4. “This difference between simulated [i.e. model output] and observed trends could be caused by some combination of (a) internal climate variability, (b) missing or incorrect radiative forcing and (c) model response error“. [WGI contribution, chapter 9, text box 9.2, page 769]


1 – According to statistical practices the trend in temperature from 1998 to 2012 (the 15 years prior to the report being drafted) falls somewhere between slight warming and slight cooling. In other words there is no certainty that any warming occurred.

2 – Despite claims of the accuracy of climate models most of the model runs (97%) wrongly predicted warming from 1998 to 2012.

3 – The IPCC is admitting that “some models” – we are not told how many, so maybe it’s almost all – exaggerate the influence of CO2 and other greenhouse gases.

4 – The models could be wrong for a number of very basic and general reasons; the IPCC really doesn’t know why the models failed.

John McLean, Leading IPCC reviewer.

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