Is climate sensitivity=3 from the IPCC a dangerous mistake?


A single number "3" is the basis for all climate projections and for all climate policy,

including NetZero. (Zero Emissions 2050).

If the number gets even slightly higher, the whole climate policy falls.


All politicians and all citizens should think deeply about the implications.

This concerns absolutely everyone and it may be the most important point

in the whole climate discussion.


The well-known climate scientist Professor Johan Rockström writes:

If climate sensitivity is 4-5 degrees rather than 3 degrees,

then the entire remaining emission budget disappears in one fell swoop.

Nor can we stop global warming at 1.5 degrees.


The IPCC has been claiming for 40 years that the climate sensitivity is 3, which means that the Earth's

temperature rises +3C for every doubling of CO2 levels.


The following well-known blue text from the IPCC, is a very accurate

mathematical consequence of climate sensitivity 3. This text has formed

the climate law in Sweden and EU and the NetZero policy (Zero Emissions 2045).




Professor Svante Arrhenius used basically the same formula (*Ref1)

120 years ago but claimed climate sensitivity=6


James Hansen, formerly of NASA and one of the world's foremost

climate scientist, showed already more than ten years ago that

climate sensitivity, when including slow feedbacks, ends up being

6 degrees.


Climate sensitivity is a measure of how strongly a planet is warmed by CO2.


The higher the climate sensitivity, the higher the forecast for warming.

If we look at today's situation using Svante Arrhenius' 120 year old logarithmic formula (*Ref1)

we get valuable and interesting conclusions. The same formula is used today

by scientists and the IPCC.  


The IPCC has been calculating for 40 years with climate sensitivity 3.

Model: the Earth is in an oven holding +1.7 C right now (*Ref2)

while the Earth itself is +1.1C

We know from NASA that the Earth is currently warming by +0.035 C/year.

If all emissions are stopped today, the Earth will reach +1.7 C in about 17 years. (*Ref3)

After that, global warming stops.

One could argue with good will that 17 years is almost zero.

Then the last report from the IPCC is true, claiming that the temperature

stops immediately when emissions are stopped. The whole world's climate policy

NetZero rests on this foundation.


If we instead believe in James Hansen and count on climate sensitivity 6:

The Earth is then in an oven holding 3.5 C right now (*Ref4)

while the Earth itself is +1.1C

As  said, we know from NASA that the Earth is currently warming at +0.035 C/year.

If all emissions are stopped today, the earth will reach +3.5 C in 70 years (*Ref5)

If all emissions are stopped by 2050, as NetZero prescribes, it will only be

far worse than +3.5 C.


This has huge consequences.

It is no longer true that the Earth's temperature will stop when emissions are stopped.

Then the whole foundation of NetZero (Zero Emissions 2050) falls and it is not in

human power to prevent +3.5 C with zero emissions as tools.


Quote Johan Rockström: .... then the entire remaining emission space disappears in one fell swoop.

Nor can we stop global warming at 1.5 degrees.


As I said, it is not in human power to prevent +3.5 C with zero emissions.

Even if the whole world converts to solar, wind and electric cars today

it's not nearly enough.


Much tougher action is needed. Relatively simple maths shows that 200 Gt of CO2

and 2 Gt of methane must be sucked out of the atmosphere every year.

Starting no later than 2025. Then we can meet the Paris Agreement

and at that rate the entire atmosphere will be restored to 18th century atmosphere within 30 years.


Atmospheric methane has 120 times the greenhouse effect of CO2.

If 1% of atmospheric methane is added to diesel, the fossil fuel becomes climate neutral. In this way

the world can become climate neutral decades sooner than what NetZero policy can offer.

Society doesn't have to be brought to its knees by astronomical fuel prices.

If we continue towards NetZero but miss all the innovative measures, a bottomless misery awaits soon.

If all this is done smartly, we can continue to raise living standards to levels that we cannot

imagine today. Quote Vinod Khosla: We can invent the future we want, as long as the experts don't stop us.


This very likely scenario with climate sensitivity >= 6 needs to be brought up for discussion.

The issue should fill the press and media and be treated as possibly the most important issue in the whole

climate work.


Quote Rockström:

We live in a new risk landscape. A climate sensitivity of 3 degrees is already an enormous challenge. We have to become fossil-free in a generation. But the mere fact that the most sophisticated climate models point to the risk of higher sensitivity calls for reflection, caution and, above all, action.


Action is needed. Climate action may look very different in the future.

A forthcoming article will attempt to address this theme in detail.


Bengt Ovelius




(*Ref1)     Formeln är 1.443*cs*ln(ppm/275)  

(*Ref2)     1.443*3*ln(410/275) =1.7 C

(*Ref3)     (1.7-1.1)/0.035 =  17 år  

(*Ref4)     1.443*6*ln(410/275) =3.5 C

(*Ref5)     (3.5-1.1)/0.035 =  70 år      


All quotes from Professor Johan Rockström come from the article

Den heliga graal, klimatkänsligheten, skakas i grunden, SVD 2020-07-18