Multi-Decadal Climate Model Testing Requirements – A Summary

In this post, I summarize two necessary requirements for multi-decadal global climate models to be met before multi-decadal projections for the coming decades should be communicated to stakeholders and policymakers.  I have discussed this in past posts (e.g. see), but am motivated to summarize here in light of the recognition (finally) of the inability of researchers to attribute changes in disasters to changes in climate statistics, as discussed in my son’s post

A Handy Bullshit Button on Disasters and Climate Change

In terms of testing the models, necessary conditions (but still not a sufficient condition) for the models to have any credibility to predict the future climate on decadal time scales are:

1. They must accurately simulate (hindcast) the statistics of major atmospheric and ocean circulation features over the last few decades (since real world data is available)


2. They must accurately simulate (hindcast) the statistics of the changes in the statistics of these major atmospheric and ocean circulation features over the last few decades.

If they cannot do both #1 and #2, they must be rejected as robust predictive (projection) tools for the coming decades.

A rationalization that the climate forcing in the coming decades could be outside of what has occurred in the past does not in any way remedy this deficiency. If they cannot skillfully predict #1 and #2, model predictions of the coming decades, published in journal articles, news reports, and climate assessments, are misinforming and misleading  stakeholders and policymakers.

In terms of #1, there is progress, as reported, for example, in

Guest Post Titled “Decadal Prediction Skill In A Multi-Model Ensemble” By Geert Jan van Oldenborgh, Francisco J. Doblas-Reyes, Bert Wouters, Wilco Hazeleger.

but there is no evidence that I am aware of satisfying #2. Even with #1, we could use reanalyses and have no need for the climate hindcasts (other than to investigate climate processes).

The real barrier that must be overcome is #2.  To date, to my knowledge, this issue has not even been discussed as part of the current IPCC assessment. They clearly have more work to do.

If, however, the IPCC ignores the need to satisfy #1 and #2 but they present projections as part of the IPCC reports, policymakers, the public and impact scientists should be ready to press the “bullshit button”.

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