Climate sensitivity and the warming pattern

By Die kalte Sonne
(German text translated/edited by P Gosselin)

In March 2018, we reported on a paper that derived the sensitivity of our climate system with the best data available. Lewis/Curry (2018) came to the result: 1.3 °C for doubling the CO2 content of the atmosphere during the rise (Transient Climate Response), long-term equilibrium (ECS) at 1.7 °C (see Table 3 of the paper).

The numbers hardly react sensitively to the choice of (larger) time windows, they fluctuate very little, whether one evaluates 1870…2016 or 1930…2016. There was a whole series of precursor studies also from other authors who also had found near these quite small values. Also papers examining historical periods (last glacial maximum to pre-industrial) do not contradict these low figures.

So the much more dramatic sensitivity estimates, especially from GCM model considerations (for General Circulation Models) — 1.86 °C for TCR and 3°C for ECS — are not applicable? “It’s not that simple,” some activists say, because the low sensitivity of the Earth’s climate would not necessitate urgent action to reduce greenhouse gases.

So how can we save the GCM from empiricism with its worrying projections? A key argument so far is this: models predict a different spatial distribution of ocean warming than what we observe:

 

Fig.3: The warming patterns derived by models (top) and the observed patterns. Of particular importance is the fact that the CMIP5 models indicate a rather uniform warming of the tropical Pacific as a result of the (mainly man-made) forcing (hence the Model-Mean), but the observations show a significantly stronger warming of the western tropical Pacific compared to the eastern one.  The images were generated with the KNMI Climate Explorer.

So it could well be, activists say, that the deviation would be just a “whim of nature”, an internal variability, and after an end of this rather random episode, the warming becomes much stronger on a global scale as to the models. There is talk of “trajectories” which were and will be possible, and the observations strongly deviate negatively because they are only a random one of the possible warming patterns. In short: “What we have observed so far is not the real reality, but it will certainly get much worse. Believe the climate models!”

2 new papers

Here we present two current papers that provide explanation. To start with: The observations of the warming rate are correct, the deviating patterns of the climate models are caused by their inadequacies and the patterns will not change.

In Dong et al (2019), the authors show that if the convective regions with many clouds in the western Pacific warm up more strongly than those with hardly any convection in the eastern Pacific, the overall global warming is much less pronounced.

Let’s take a look at the clouds in the tropical Pacific:

Fig. 4: The convection(CAPE Index) over the tropical Pacific. The west-east gradient can be seen clearly. Source.

Convection in the western tropical Pacific leads to an increased heat radiation into space, which means that the warming there can be reduced much more effectively than would be possible with a stronger warming of the eastern Pacific with less convection, cf. Fig. 4. The paper finds:

For the west Pacific patch, warming is communicated to the upper troposphere, which warms the whole troposphere across all latitudes, causing a large increase in outgoing radiation at the TOA. Furthermore, the patch of warming locally decreases tropospheric stability, measured here as estimated inversion strength (EIS), but increases EIS remotely over tropical marine low clouds regions, yielding an increase in global low cloud cover (LCC) which enhances the global SW reflection….The results first highlight the radiative response to surface warming in tropical ascent regions as the dominant control of global TOA radiation change both in the past and in the future. …This surface warming pattern yields a strong global outgoing radiative response at TOA that can efficiently damp the surface heating, therefore producing a very negative global feedback.”

It is therefore a clear physical mechanism that leads to the observed stronger warming of the tropical West Pacific leading to lower global sensitivities (= stronger negative global feedback).

The second paper, Seager et al (2019), deals with the same phenomenon and concludes that the observed pattern is not random, but a direct result of forcing. It states:

The main features of observed tropical Pacific climate change over past decades are consistent with a response to rising CO₂, according to fundamental atmosphere and ocean physics….However, the strength of the tropical Pacific influence on global climate implies that past and future trends will diverge from those simulated by coupled climate models that, due to their cold tongue bias (ein Streifen kühleren Wassers in Äquatornähe des Ostpazifiks, d.A.), misrepresent the response of the tropical Pacific to rising CO₂.”

Climate models have such large deficits in the depiction of events in the tropical Pacific that they are globally incorrect in determining the response to the forcing (see Fig. 3) and systematically overestimate the sensitivity to the forcing (according to Seager et al, and Dong et al).

So will we read anything about this in the media? A possible headline might be: “Climate models calculate the future too hot! Don’t hold your breath.

PlayStation climatology

We eagerly await to see whether the results of these two important studies will even be included in the IPCC’s forthcoming progress report. Here hundreds of pages dealing with model projections would have to be critically revised. One more reason for us to trust empiricism and “PlayStation climatology”.

But what is to become of the “panic” which Fridays for Future wishes to impose on us? Policymaking is hot because the models are too hot. Which scientists have the courage to be responsible and to enlighten FFF and policymaking?

via NoTricksZone

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July 17, 2019 at 11:56AM