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#ECS in the real world: Skeie et al. 2014

13 Dec 2023 | Science Notes

This week’s entry in the ECS-below-2 pileup comes from a group of scientists from Norway who we already heard from when we looked at Aldrin et al. 2012. This time the lead author is RB Skeie, but most of the names are the same as the Aldrin paper, just in a different order. Also much of the data is the same, as is the method. And the result is the same too: ECS comes out at 1.8C, just below the Aldrin estimate of 2.0C. So why the separate paper? They used a bit more data, and made some slight improvements to the method. And with that the estimate went down. Follow the science, we say.

Once again the Norwegian group combined three surface temperature data series with three ocean heat content estimates. In the earlier paper they used the ocean data one series at a time, but in the new paper they combined them all into one set. And they used an updated radiative forcing approach called “effective radiative forcing”, which takes account of how the influence of greenhouse gases and other climate drivers varies over space. Finally they used updated aerosol pollution data, which they found had a smaller cooling effect than had previously been estimated. The importance of this last tweak was that the more cooling you get from aerosols, the more warming you have to get from greenhouse gases to match the historical record. So if newer data shows aerosols haven’t done a lot of cooling, that implies greenhouse gases can’t have done a lot of warming.

Which is what they find: the ECS of the climate system is lower than previously thought, at around 1.8C. Doubling CO2 will warm the climate system over the long term by only 1.8 C, which as the authors point out is “below the lower limit of the likely range (>66% probability) for the ECS of 2 to 4.5 C in IPCC AR4 (Meehl et al., 2007)”. So in 2007 the IPCC declared it “likely” that ECS had to be above 2C. The data, meanwhile, say the best estimate is only 1.8C.

Who’re ya gonna believe, the IPCC modelers and guesstimators, or the real world data? You can’t believe both, so we’re more inclined to go with the data, which as we’re seeing, is telling us that equilibrium sensitivity to CO2 is 2 degrees C or less.

One comment on “#ECS in the real world: Skeie et al. 2014”

  1. I'm still convinced that the ECS, including all feedbacks is Net Zero 😉
    That is, at the current concentrations and temperature, adding more of the stuff will barely do anything. The physical limit is about 1 degree C for a doubling anyway and there is NO evidence for positive feedbacks (other than 'tipping points' that have been crossed but never seem to actually tip), but there is some evidence for negative feedbacks.

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