Loop gain of the climate system – Or why high positive feedback is impossible

Since the loop gain in the climate object cannot exceed 0.1 (at maximum) without rendering the climate so prone to instability that runaway feedbacks that have not occurred in the past would be very likely to have occurred, the maximum feedback sum before mutual amplification cannot exceed 0.32: yet the IPCC’s implicit central estimate of the feedback sum is 2.81.

From the engineering standpoint – which is where I come from – this is my biggest irk with the "loudest predictions" of the climate sciences: That there are so strong positive feedbacks, that not only do we get a rise of 4 °C (or more) per doubling of the CO2 level, no, we also risk a "runaway climate".

I say this such high sensitivity is bullshit.

If climate would be this sensitive, the oceans would have boiled away long ago.

To understand it a bit better, one needs to know that there are three "concepts" (sorry, don't know a better english word) with relation to CO2 and temperature:

• Sensitivity
• Forcings
• Feedbacks

Sensitivity is the total sum of effects that CO2 has on the temperature. A doubling of CO2 in the atmosphere is usually taken as the input (let's say from 0.03% to 0.06%), and various models predict the total temperature change ("sensitivity"). The IPCC report, which is supposed to represent the available peer-reviewed literature, says that the climate sensitivity ranges from somewhere between 2 °C to 4.5 °C, with certainly no less than 1.5 °C.

How do they come to this high sensitivity? The direct effect of CO2 on temperature (by filtering out radiation that would have otherwise escaped into space – the so called "greenhouse effect") is called forcing and it is around 1 °C – and this number is consent between the vociferous mainstream ("alarmists") and the skeptics ("deniers"). I don't know of anybody that disputes the size of the CO2 forcing being around 1 °C (give or take a bit), and I surely do not "deny" it.

So where does all the heat come from? The other half of the CO2 equation is the feedback. Feedback are all secondary effects that react to a temperature change: Cloud coverage, glacier coverage, and so on. These changes itself lead to a temperature change as well, because they change how much heat is radiated back into space. The vociferous mainstream says that for every degree of change (no matter the source, whether CO2 or vegetation or continental drift or tilt of the earth axis) there will be up to another 3.5 degrees of change in the same direction – a strong positive feedback.

And that's where anybody should say: No way. No way is it possible to have a stable climate with this kind of feedback. Well, at least some of the climate skeptics say it, that there is a negative feedback.

By the way, the biggest contributor to feedback are clouds – but that is a topic for another day…