How Long Is The Pause?

  • Date: 01/09/14
  • Judith Curry, Climate Etc.

With 39 explanations and counting, and some climate scientists now arguing that it might last yet another decade, the IPCC has sidelined itself in irrelevance until it has something serious to say about the pause and has reflected on whether its alarmism is justified, given its reliance on computer models that predicted temperature rises that have not occurred. – Rupert Darwall 

The statement by Rupert Darwall concisely states what is at stake with regards to the ‘pause.’   This seriously needs to be sorted out.  Here are two recent papers that contribute to setting us on a path to understand the pause.

HAC-Robust Measurement of the Duration of a Trendless Subsample in a Global Climate Time Series

Ross McKitrick

Abstract. The IPCC has drawn attention to an apparent leveling-off of globally-averaged temperatures over the past 15 years or so. Measuring the duration of the hiatus has implications for determining if the underlying trend has changed, and for evaluating climate models. Here, I propose a method for estimating the duration of the hiatus that is robust to unknown forms of heteroskedasticity and autocorrelation (HAC) in the temperature series and to cherry-picking of endpoints. For the specific case of global average temperatures I also add the requirement of spatial consistency between hemispheres. The method makes use of the Vogelsang-Franses (2005) HAC-robust trend variance estimator which is valid as long as the underlying series is trend stationary, which is the case for the data used herein. Application of the method shows that there is now a trendless interval of 19 years duration at the end of the HadCRUT4 surface temperature series, and of 16 – 26 years in the lower troposphere. Use of a simple AR1 trend model suggests a shorter hiatus of 14 – 20 years but is likely unreliable.

McKitrick, R. (2014) HAC-Robust Measurement of the Duration of a Trendless Subsample in a Global Climate Time Series. Open Journal of Statistics, 4, 527-535. doi: 10.4236/ojs.2014.47050. [link] to full manuscript.

JC comment:  I find this paper to be very interesting.  I can’t personally evaluate the methods, although I understand the importance of the heterskedacity an autocorrelation issues.  The big issue with length of the pause is comparison with climate model predictions; I would like to see the climate model simulations analyzed in the same way.  I would also like to see the HadCRUT4 results compared with Cowtan and Way and Berkeley Earth.  I also seem to recall reading something about UAH and RSS coming closer together; from the perspective of the pause, it seems important to sort this out.

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