A pertinent climate question
by Michel de Rougemont
Not so innocent as it looks, a pertinent question is asked by Judith Curry on Twitter:
How much of a change in cloudiness would it take to account for the 0.53 W/m2 increase in TOA radiative forcing since 2003?
She asks it in relation with a recent article accepted for publication on Observational evidence of increasing global radiative forcing (Kramer et al., 2021).
Abstract. “Changes in atmospheric composition, such as increasing greenhouse gases, cause an initial radiative imbalance to the climate system, quantified as the instantaneous radiative forcing. This fundamental metric has not been directly observed globally and previous estimates have come from models. In part, this is because current space‐based instruments cannot distinguish the instantaneous radiative forcing from the climate’s radiative response. We apply radiative kernels to satellite observations to disentangle these components and find all‐sky instantaneous radiative forcing has increased 0.53±0.11 W/m2 from 2003 through 2018, accounting for positive trends in the total planetary radiative imbalance. This increase has been due to a combination of rising concentrations of well‐mixed greenhouse gases and recent reductions in aerosol emissions. These results highlight distinct fingerprints of anthropogenic activity in Earth’s changing energy budget, which we find observations can detect within 4 years.”
This question touches a central point of climate science because it cannot be an experimental science in which one can play with parameters in isolation from each other. Only a few limited ongoing instrumental observations and palaeolithic reconstructions may serve to try to distinguish natural from anthropogenic processes, in particular radiative forcing processes. However, most of this job, if not all of it, takes place in silico.
The question can also be formulated in a more general way:
Is it at all possible, at global scope and by instrumental observations, to distinguish the causes of radiative forcing difference of 0.53 W·m-2 over a time period of 15 years?
To the cloudiness suggestion:
- From a simple, two-layer energy balance budget it can be estimated that, all other things remaining constant, a 1% increase in cloudiness (which amounts to approx. 66% overall) may induce a temperature increase of 0.54 °C at the Earth surface and of 0.45 °C at the top of atmosphere (TOA)
- Without consideration for any system feedback, a radiative forcing of 0.53 Wm-2 would induce a temperature rise of 0.11 °C at the surface, and 0.18 °C at TOA.
- To obtain a same temperature increase, thus to respond to a forcing of 0.53 Wm-‑2, it would take a change in cloudiness by 0.27 % for the surface, or by 0.4 % for the TOA.
- Is cloudiness, or change of cloudiness, measurable with such accuracy and precision at the aggregated global scope? What was it in 2003, and in 2018?
From an overall energy balance perspective:
- In general, and to simplify, modelers estimate all incoming and outgoing heat fluxes, and let any remaining quantity warm or cool the oceans, thus reporting a so-called accumulated ocean heat or “heat content anomaly”.
According to NASA, over the 1993–2019 period, a heat flux anomaly of 0.36 to 0.41 Wm-2 for the first 700 m of depth would have accumulated. Over time, other heat release periods should also occur so that the imbalance does not let us boil or freeze for ever (it never did).
- Over this time period of 26 years, this heat flux would have implied a temperature change to a well homogenized 700-meter water column of 0.10 to 0.11 °C, a hard to measure change.
- A question, similar to the previous one, arises regarding instrumental observation: is it at all possible to measure such heat accumulation precisely, accurately, and at the aggregated global scope (by localized temperature monitoring or any other valid method)?
In all these evaluations, errors will have to be taken into account; those arising from instrumental imprecisions and inaccuracies, those that are embedded in the data massaging process (averaging over time and locations), and systemic ones deriving from incomplete and imperfect model designs, their parametrization and simplifications.
Said differently: the resulting balance sheet of any model should entail an account for garbage; but it appears that it is at the same time the energy accumulating in oceans. The NASA-Goddard simplified representations does not show any; others (Trenberth, Fasullo, & Kiehl, 2009) show an “net absorbed” of 0.9 W·m-2 or the U.S. Global Change Research Program (USGCRP) indicates a “Surface imbalance” of 0,6 ±0.17 W·m-2 (one appreciates the margin precision). However, taking into account all potential errors, the true range of validity of this imbalance may well be of the order of hundreds of percent, thus challenging the narrative of a ticking time bomb accumulated in the ocean depths.
One final question must be addressed to the climate science community: will the heat accumulated in the oceans ever be realized by the surface climate?
Kramer, R. J., He, H., Soden, B. J., Oreopoulos, L., Myhre, G., Forster, P. M., & Smith, C. J. (2021). Observational evidence of increasing global radiative forcing. Geophysical Research Letters, 48(e2020GL091585). https://doi.org/10.1029/2020GL091585
Trenberth, K. E., Fasullo, J. T., & Kiehl, J. (2009). Earth’s global energy budget.
Bulletin of the American Meteorological Society, 90(3), 311–323. https://doi.org/10.1175/2008BAMS2634.1
About the author:
Michel de Rougemont, chemical engineer, Dr sc tech, is an independent consultant. www.mr-int.ch
In his activities in fine chemicals and agriculture, he is confronted, without fearing them, to various environmental and safety challenges.
He published a book ‘Réarmer la raison‘, on sale at Amazon, and an essay ‘Entre hystérie et négligence climatique‘ (both in French only).
He maintains a blog blog.mr-int.ch,, a site dedicated to the climate climate.mr-int.ch, as well as one on biological control in agriculture biologicals.mr-int.ch
He has no conflict of interest in relation with the subject of this paper.
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