Real Global Temperature Trend, p4 – If Aerosol Cooling strongly overestimated(?), then Climate Sensitivity is low, says cherry pick study

Several studies suggest global dimming aerosol cooling is not overestimated, but underestimated. But in our quest to uncover ‘The Real Global Temperature Trend‘ – we need to be open for all possibilities – even the bizarrely unsatisfying slap in the face of sometimes encountering ‘possible good news’ (God No!) while again skipping breakfast to read through piles of climate journals, even the low impact ones. The dark corner of the scientific library. We found a picture of a naked scientist once. Today it’s worse:

Yes. We found one. One paper that suggests aerosols may not cool as much*, written by Bjorn Stevens, a meteorologist at the Max Planck Institute for Meteorology, and published in the Journal of the American Meteorological Society.

The science is in essence rather simple. Aerosols – extremely complicated and poorly understood as they are – are [even climate deniars somehow find that bit easy to agree on] net climate coolers. If that cooling effect turns out to be underestimated – as several scientists suggest – CO2′s positive climate forcing must be higher (to explain observed temperatures). If aerosol cooling however is overestimated, the opposite holds true – and CO2′s positive climate forcing would be lower.

*) His model suggests aerosol cooling can not be lower than -1W/m2. Mind you, that is a BIG difference compared to the study (that did manage to get published in a slightly higher-esteemed journal) we reported on yesterday, that said aerosol cooling (if you look at direct (global dimming) and indirect effects – and regard the atmosphere as a 3D model – with different effects at different atmospheric altitudes) combining all forcing effects, would amount to as much as -4.4W/m2.

And we also found someone, a known climate skeptic ‘who’s had a career outside academia‘ (financial world) who has found a real climate scientist(?) without very many friends (Judith Curry of Georgia Institute of Technology) willing to co-author a climate model study using that lowered value for aerosol cooling (for extra dramatic results they go even 0.1 lower! → -0.9W/m2) over a peculiarly select range of the historical climate dataset – and then found the journal Climate Dynamics willing to publish their results, in 2014. [Next week I'll try to get my groceries list published. I'll have it peer reviewed by my supermarket – trustworthy folks.]

The authors looked at two periods in the historical climate dataset that are ‘not too strongly influenced by volcanic eruptions’ (major aerosol emitters) – namely 1859-1882 as base period and 1995-2011 for the final period. Wow. That’s just 23 years for the base line – and 11 years for the ‘modern period’ (a cherry pick in itself, as that is more or less ‘the ENSO temperature plateau‘). You wonder why. Why you would want to make a cherry picking exercise that obvious – to even include a graph:

If you use very small value for aerosol cooling and you cherry pick historic climate data, climate sensitivity is suddenly lower
Tadaa! If you use very small value for aerosol cooling, ignore additional climate forcing stuff you find too complicated, and you cherry pick historic climate data, CO2 climate sensitivity is suddenly lower. Science is magic!

Then if they add an aerosol cooling of just -0.9W/m2 (again, very strange) in their climate model, and ignore the periods where aerosol cooling is very well documented (precisely those volcanic eruption peaks they deliberately ignore) no one might notice how skewed the results are: a ‘most likely’ (95%) climate sensitivity value between 1.25 and 2.45 degrees Celsius – with a median estimate as low as 1.64 degrees.

Not including aerosol peaks in the model results points to the fact that the inserted value for aerosol cooling is extremely small and unlikely to be true. A peak of a flawed value never looks good on results. And then even the lesser journals might not have published. Although the cherry pick was equally obvious – for any editor wearing their glasses.

Funny thing. Climate psychology. Here at Bits of Science we’re completely immune.

Good thing we now have established our bottom line for weakest model-based climate sensitivity calculation. The search for ‘The Real Temperature Trend’ goes on. We’ll have another update tomorrow!

© Rolf Schuttenhelm |

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