Comments on New "World Weather Attribution" Analysis of Australian Bushfires

By Michael E. Mann on Tuesday, March 3, 2020 - 23:53

As some readers will know, I happen to have been on sabbatical in Australia these last past months. I came there to study the impact of climate change on extreme summer weather events with a specific focus on Australia. Only to arrive in mid December just in time to encounter the most profound example on record.

I have witnessed and written about the unprecedented heat, drought, and bushfires during the historic austral summer of 2019/2020 and the role that climate change played in these events.

A brand-new analysis from the "World Weather Attribution" (WWA) group provides a rather confusing and murky assessment of the role played by climate change in these historic events, so I have taken this opportunity to provide a brief review and critical assessment of this new (un-reviewed) analysis.

The now-famous Garnaut Climate Change Review concluded back in 2008 that the Australian bushfire season would "start earlier, end slightly later and generally be more intense” and that "his effect increases over time, but should be directly observable by 2020”. That prediction is based on the simple fact that if you combine extreme heat and extreme drought, you get faster-spreading, more intense, more widespread bushfires.

Whether climate model simulations capture the impact climate change is having on these extremes is another question. The WWA group concede that the models they analyzed FAIL to do so. To me this somewhat burried sentence is the most important sentence in the new WWA release (emphasis added):

As the trend in extreme heat is one of the main factors behind this increase and the models underestimate the observed trend in heat, the real increase could be much higher. This is also reflected by a larger trend in the Fire Weather Index in the observations.

By the way, underestimate the heat and you'll likely underestimate the intensity of the drought (which is fueled by heating). If you can't capture the magnitude of the heat and the magnitude of the drought you're not going to capture the intensity and scale of the resulting bushfires.

This underscores a point that I have made repeatedly. Current generation climate models are simply not up to the task of extreme event attribution in many cases. They are not capturing key atmospheric mechanisms behind many extreme summer weather episodes that are almost certainly being influenced by climate change.

I explained these reasons behind this in a Washington Post op-ed from a little more than a year ago (which is based an a study we published in Science Advances that demonstrates the key role of the atmospheric mechanism of planetary wave resonance that is not well-resolved by current generation climate model.

It’s not a coincidence that we saw record heat, record drought and record bushfires this summer in Australia. Climate change has lead to more extreme summer heat and the poleward displacement of prevailing winter storm tracks, along with the extreme heat and drought has provided a "perfect storm" for the sorts of unprecedented bushfires we witnessed this past summer. Whether or not current generation climate models are up to the task of faithfully reproducing the underlying processes involved and identifying the connection with climate change is, in my view, somewhat irrelevant to whether or not we can draw the obvious connections.

In my view, groups like the World WWA have to be more up front about the caveats of these attribution exercises. Otherwise, they are potentially misleading the public and policymakers by understating the role that climate change is playing in these unprecedented weather extremes.

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