Thorsten_Mauritsen

Wed, 20 Oct 2021 08:16:14 +0200

Senior Lecturer in Climate Science, Department of Meteorology, Stockholm University

Thorsten Mauritsen,

 

Thorsten,

The undersigned is an engineer and innovator and I have decades of experience in calculating complex thermodynamic processes and running computer simulations. I have also used my mathematical tools since 2008 to keep an eye on the climate.

Understanding the climate in depth plays a crucial role in sketching the innovations needed to solve the climate crisis.

I read with interest your debate article in DN, and debate means exactly that: debate.

My opinion piece is here. https://ppm.today/index.html?bilden-av-att-det-aer-foer-sen.htm

I will publish the answers/replies you give in both Swedish and English

It would be best if DN would spin on this thread.

Many thanks for future replies.

We are fighting from a disadvantage but must help to change the direction of Glasgow so that climate policy really solves the climate crisis.

Best regards

Bengt Ovelius

 


Hi Bengt,

 

It is true that if the climate sensitivity is 36 K then it probably follows that most of the conclusions drawn are wrong. Fortunately, the problem lies in your calculations, thanks for sharing these!

 

Ice ages are driven by variations in the Earth's orbit around the Sun, which causes ice caps to build up in certain places, which in turn cools the Earth. Exactly how this happens is still debated, but that it has happened is a fact. As the Earth cools, the amount of carbon dioxide in the atmosphere is also reduced as it is absorbed by the oceans, just as beer is better when it comes out of the fridge than when it has been in the sun for a few hours. In this case, this decrease is to be counted as a feedback mechanism, leading to a slightly larger decrease in temperature.

 

Now if we assume, as you do, that the cooling of the Earth is caused by the decline in carbon dioxide, then we arrive at large climate sensitivities. This is a somewhat old debate, but one that was re-energized recently when Snyder (2016) published an estimate of 9 K. This is a bit lower than yours, but can probably be largely explained by the fact that the temperature at Vostok is not representative of global mean temperature and that you have to convert the carbon dioxide content to a radiative forcing. That this leads to the wrong conclusions is explained by Schmidt and colleagues in a follow-up comment. I attach both as I don't know if you have access to these.

 

Overall, however, this makes the ice ages a rather poor source of information on the Earth's climate sensitivity. Since no method is perfect, the approach has instead been to weigh different sources, with different advantages and disadvantages, into an overall estimate. You can read more about this in Sherwood (2020,  https://doi.org/10.1029/2019RG000678), and in IPCC AR6 Chapter 7.5 which is available at ipcc.ch. The actual methodology of the aggregation is different in these, but the conclusions will be the same.

 

Greetings,

Thorsten

 

 


Many thanks Thorsten

This is the first post that takes the discussion forward properly.

I also say in my summary that everyone will be happy if I am wrong, including me.

The consequences of climate sensitivity=36 are uncanny.

Then comes the next crunch question:

If you just plot all VOSTOK as scatterplot - CO2 - Temp anomaly over 400,000 years it becomes like a cloud.

If you just plot all NASA measurements last 100 years it becomes a stick. All these are cold facts, aren't they ?

In 20,000 years scientists will come and do similar scatterplot on earth. It seems logical that the stick has settled into the cloud as the animation shows ?

These scientists will not see a stick.

My suspicion is that the IPCC scientists have been staring blind at the stick of unstabilized values that very correctly exhibit climate sensitivity=cs= 3

The slope of the stick also reveals much. If 100 years of emissions (110 ppm) occurred in a single day, the stick would have been horizontal

If 100 years of emissions (110 ppm) occurred in 10,000 years, the stick would have been hidden in the cloud from the start.

The tip of the stick, which rises at 0.035 C/year, would then require about 700 years to migrate into its place in the cloud.

 

climatesensitivity2

 

Then comes the next question, which is not so dependent on climate sensitivity:

It is described here https://ppm.today/index.html?klimatet-just-nu.htm

MVH Bengt Ovelius

 

 

The animation is available here: https://ppm.today/index.html?thorsten-mauritsen.htm


 

Hi Bengt,

 

Yes, I can answer that too. The reason that the temperature increase stops when you bring carbon dioxide emissions down to zero is thatthe deep oceans absorb carbon dioxide at about the same rate as they absorb heat. Here is a more detailed explanation:

 

When you gradually increase carbon dioxide in the atmosphere by burning fossil fuels, as we are doing now, the deep oceans "lag" and absorb heat because of their enormous heat capacity which, as you rightly point out, causes the surface temperature to be out of balance with the increased greenhouse effect. You say you are following a transient, and the relevant sensitivity is the TCR which in round loops is half the climate sensitivity. If you keep (somehow magically) the carbon dioxide content at a certain level, the deep oceans will eventually warm up too, and then you reach the equilibrium temperature.

 

The carbon dioxide we emit is distributed primarily between the atmosphere, vegetation and the mixed layer of the oceans (the top 50-100 metres). When we stop adding new fossil carbon dioxide, the deep oceans and various other processes will slowly reduce the amount of carbon dioxide in the atmosphere.

 

Since ocean currents draw both heat and carbon dioxide down to the deep ocean, these two processes compensate for each other, leading to roughly constant temperatures after we stop burning fossil fuels. After about 100 years, the temperature decreases very slowly.

 

In practice, there are some subtleties that make this not quite right. Mainly, it's a bit faster to bring down carbon dioxide levels, mainly because processes other than the oceans can also contribute. Then there are some short-lived forcings associated with fossil fuel combustion, mainly aerosols and methane leaks, which when removed lead to a little extra warming.

 

I attach some relevant studies, but of course there is more on this in the IPCC report chapter 5.

 

Greetings,

Thorsten

 

Ref PDF

MacDougal_etal_2020

Mauritsen_Pincus_2017

 

 


Thorsten

 

Many thanks for interesting comments!

 

You write.......

>>therelevant sensitivity is the TCR which in round loops is half of the climate sensitivity.

If you calculate with the wrong global climate sensitivity, the TCR will also be wrong, right ?

 

I see two worlds in front of me,

One with climate sensitivity 36 which is in harmony with Vostok, with 420C@100%, and with 275 and 285 points.

One with climate sensitivity=3 that gives +2C at 450 ppm in 2100

clip4793

If at some point in the future we agree that climate sensitivity=3 is wrong, then the question is which cs would you advocate.

How does this new, more likely cs affect the value of the TCR and thus the thermal balance of the oceans?

 

Best regards

Bengt