Dr. Judith Curry on Estimating Climate Risk Using Models that Fail Backtests

Representative Concentration Pathway - Wikipedia

IPCC AR5 (2014) presents 4 emission pathways which are at the heart of the climate change debate. There are a range of other topics that are also debated – notably, the atmospheric and ocean physics effects from GHG concentrations assumed. Those effects are further attenuated by factors that modeled by IPCC such as a more robust coupled atmospheric-oceanic physics, astrophysical and geophysical dynamics.

The emission scenario dominates the first order effect produced by the IPCC climate models. That first order effect is amplified by the transient climate sensitivity (TCS – the feedback effect from higher concentrations.

So, depending on which RCP scenario you assume, you can get a wide range of effects.

Oh, and not to go off-point too far, TCS estimates are now coming in at 1/2 – 1/3 below early nightmare assumptions

Anyway, back to the point.

CarbonBrief provides a very intelligent analysis of the RCP scenarios (https://www.carbonbrief.org/explainer-the-high-emissions-rcp8-5-global-warming-scenario). It’s worth a read if you have even a casual interest in this subject.

It’s also worth reading the origin of these scenarios starting with van Vuuren et al. (2011). Among other things, CarbonBrief warns against using RCP 8.5. Quoting Professor van Vurren:

“RCP8.5 has probably become less likely compared to 2008-2011, when the scenario was developed and published. The reason is that since that time several countries and companies have adopted climate policy inspired by the Paris Agreement, but also the costs of solar photovoltaics and wind have come down much more rapidly than originally expected. Again, it does not mean that the scenario is implausible – and thus not relevant as a scenario to explore high-end forcing – but it is probably not the most likely business-as-usual case. It wasn’t originally, and it isn’t now.”

In recent years, insurance modelers have attempted to translate IPCC forecasts to economic losses. One such model by AIR does what CarbonBrief and other scientists advise not to do: use RCP 8.5.

Why does AIR use RCP 8.5? Well, why does any consultant tell a horror story? A lot of climate consultants are out there right now telling such stories. So why indeed? Cjui bono?

In a recent post, Dr. Judith Curry takes issue with an AIR model recently made public: https://judithcurry.com/2021/02/15/assessment-of-climate-change-risk-to-the-insurance-sector/

Curry offers an in-depth critique of AIR which is an otherwise well-respected company:

AIR Worldwide, a respected catastrophe risk modeling and consulting company, has recently published a report Quantifying the Impact from Climate Change on Hurricane Risk.  AIR’s assessment has three components:

  • Hazard component (relates to the frequency and intensity of events)
  • Engineering component (relates to physical assets at risk)
  • Financial component (relates to monetary losses)

The AIR Report purports to “capture the full range of plausible events that could impact an area.”

My critique focuses solely on the hazard component. A summary of my analysis is provided below:

  1. The driver for AIR’s assessment is warming associated with the emissions/concentration scenario RCP8.5, which AIR refers to as a ‘business as usual scenario.’  In fact, RCP8.5 is increasingly being judged as implausible by energy economists, and is not recommended for use in policy planning.
  2. The hurricane risk from climate change focuses on the number and intensity of U.S. landfalls in a changing climate.  Their scenario of the number of major hurricanes striking the U.S. by 2050 is judged to be implausible for medium emissions scenarios such as RCP4.5.
  3. The sea level scenarios used in the AIR Report are higher than the recent IPCC consensus assessments and are arguably implausible for medium emissions scenarios.
  4. The AIR Report ignores the ‘elephant in the room’ that is of relevance to their target period to 2050: the Atlantic Multi-decadal Oscillation (AMO). A shift to the cool phase of the AMO would arguably portend fewer major hurricanes striking the U.S.

Whereupon Dr. Curry painfully dissects AIR through a thousand cuts.

Too bad for AIR – a respected company that any physicist will likely observe in this instance their consultants got a bit ahead of themselves.

References:

AR5 Synthesis Report: Climate Change 2014. (n.d.). Retrieved February 25, 2021, from Ipcc.ch website: https://www.ipcc.ch/report/ar5/syr/

Curry, J. A. (2021, February 15). Assessment of climate change risk to the insurance sector. Retrieved February 25, 2021, from Judithcurry.com website: https://judithcurry.com/2021/02/15/assessment-of-climate-change-risk-to-the-insurance-sector/

Explainer: The high-emissions ‘RCP8.5’ global warming scenario. (2019, August 21). Retrieved February 25, 2021, from Carbonbrief.org website: https://www.carbonbrief.org/explainer-the-high-emissions-rcp8-5-global-warming-scenario

van Vuuren, D. P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K., … Rose, S. K. (2011). The representative concentration pathways: an overview. Climatic Change109(1–2), 5–31.

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