9,25 – a factor that could close the global warming debate
Guest post by Frank Lansner (hidethedecline)
The CO2-sensitivity describes the warming effect induced by a doubling of the CO2 concentration in the atmosphere, and is thus the epicentre of the global warming discussion. Estimates of the CO2 sensitivity are very different, and the value range used by IPCC appears unlikely to physically impossible. To show this, I will focus on the factor “Fw” between the total CO2 warming and then the warming from a single doubling of CO2 concentration.
The total CO2 warming effect is obviously many times bigger than the warming from a single CO2 doubling. Example: When changing CO2 concentration from 5 ppm to 320 ppm we have 6 doublings. But on top of these 6 doublings, how much warming effect is introduced when CO2 concentrations are changed from 0 to 5 ppm etc? In the following I use the online model MODTRAN:
Fig. 1. Above is illustrated the warming effect of CO2 for 3 different climatic areas. Zero W/M2 represents the net forcing of the atmosphere fore a given scenario with CO2 concentration set to 0 ppm.
For each area is shown a clear sky scenario as well as a light rain scenario. All other variables in MODTRAN are left as the default values. The results from MODTRAN are total atmosphere outgoing radiation, and thus when changing concentrations of CO2 we get total atmosphere responses incl feedbacks if present.
Fig 1 Shows 6 doublings of CO2 concentration: 5-10-20-40-80-160-320 ppm where every doubling shows warming effect of similar size (–as could be expected due to the logarithmic declining effect of adding more CO2 to the atmosphere).
From the graph above we can see that the total CO2 warming effect today equals around 9 times the warming effect of one doubling of CO2 concentration.
Fig 2. For a better compare between the scenarios on fig1, these are now shown as %-values of the total CO2 warming effect for (Forcing) with today’s concentration of 390 ppm CO2, equals 100%. It appears that clear sky, rainy sky, Arctic area, tropics, subtropics scenarios has a very similar profile indeed and I find that this result shows that we can consider these %-trends to be rather global.
Fig 3. The average global CO2-doubling can now be calculated more accurate to be near 10,8% of the full CO2 warming effect at 390 ppm. (Or, the “CO2-sensitivity” warming effect is around 10,8% of the total CO2 warming effect, globally.)
Thus, the “best estimate” of the factor between total CO2 warming effect and the warming effect from one CO2 doubling – Fw – can be calculated. Best estimate (so far) Fw = 9,25.
CO2-warming-total (K) = 9,25 * CO2-warming-from-one-doubling (K) = 9,25 * CO2 sensitivity (K)
I have used MODTRAN for this result, but it is universal that the doublings must have near same warming effect and thus the individual doubling will have just some fraction of the total value. For now, the factor 9,25 is best estimate.
Hansen – CO2 sensitivity.
Now how does the factor 9,25 between total CO2 warming effect and CO2 warming effect from a single doubling support the viewpoints of James Hansen on CO2 sensitivity?
James Hansen often refers to a CO2-sensitivity of 6 K… 6 K warming effect for each single CO2 doubling:
Fig 4 James Hansens CO2 sensitivity of 6 K gives around 55,5 K of total CO2 effect using the factor Fw = 9,25. As the total warming effect of all greenhouse gasses is assumed to have a warming effect of approx 33 K, the Hansen CO2-sensitivity demands that the total CO2 related warming effect is bigger than all the greenhouse gasses effect combined.
The overall CO2 warming effect is supposed to be around 10-15-2% of the total warming effect of the atmosphere, here we use 15%. Since CO2 is assumed to account for 15% of the total 33K greenhouse effect on Earth, the CO2 total warming effect is around 5 K. So just ONE CO2 doubling of Hansen’s CO2 sensitivity of 6 K has a bigger warming effect than the total warming effect supposed to be possible.
It is therefore highly odd that Hansen’s claim of 6 K CO2 sensitivity has been taken seriously anywhere at any time.
Here the “greenhouse wheel” (see WUWT post Wheel! – – Of! – – Silly!) where supposedly scientists imagine that we by year 2100 can have warming of over 7 K in fact with less than one CO2 doubling to cause this:
Fig 5. To account for their 7 K temperature increase, they must have played with a CO2-sensitivity of perhaps 10 K? So these honourable “scientists” believes that one CO2-doubling might resemble a third of the combined earth greenhouse effect?
IPCC – CO2 sensitivity
Then, how does the factor 9,25 between total CO2 warming effect and CO2 warming effect from a single doubling support the viewpoints of IPCC on CO2 sensitivity?
IPCC AR4 viewpoints for the CO2 sensitivity :
IPCC “best estimate” of warming from one CO2 doubling is 3 K.
Using the Fw = 9,25 we learn, that if one doubling warms 3 Km then the total CO2 warming should be around 28 K ( = 9,25 * 3 )
We must then remember again that the total warming effect of the atmosphere is generally accepted to be near 33 K. The warming effect related to CO2 should then be around 85% of the total Earth atmosphere greenhouse gas effect. And without CO2, the atmospheres warming effect should be reduced to 15% of todays atmosphere…. On a globe with mostly water-ocean surface…
The IPCC numbers where each doubling of CO2 represents 3 K it simply does not fit at all with the total warming effect of the atmosphere.
IPCC then claimed:
“Values substantially higher than 4.5°C cannot be excluded..”
Well, 4,5 K for CO2 sensitivity gives a total CO2 effect of 41,6 K. This is 126% of the total earth greenhouse effect, so we could rephrase:
“Values of CO2 related warming substantially higher than 126% of the total greenhouse gas warming cannot be excluded..” …
Idso´s and Lindzens estimates for CO2 sensitivity.
What if we assume that CO2 is responsible for the 15% of the 33K greenhouse warming effect on Earth? This corresponds to 5 K. If true, the CO2 warming from one doubling should be
CO2 sensitivity = CO2warming-total / Fw
CO2 sensitivity = 5K / 9,25 = 0,54 K
So just using the generally accepted knowledge that CO2 sholuld account for around 15% of the total Earth greenhouse effect, and using the also generally accepted knowledge that total Earth greenhouse effect is 33K, then the CO2 sensitivity should be near 0,54K
Idso 1998 suggests 0,4 K, and Lindzen suggests 0,5 K these results appears sound and realistic in strong contrast to values from IPCC and Hansen.
Hansens 350 ppm ”safe level”
Fig 6. When working with CO2 – effect, one cant help wondering what Hansens ”safe level” of 350 ppm CO2 is all about.
Fig 7. NASA´s, James Hansen has claimed 350 ppm to be a safe level of CO2:
– Just 1,5 % less Warming effect from CO2 and we are “safe”.. ?
If CO2 has a total warming effect of 5 K – as previously calculated – the difference between the Hansen “safe level” CO2 warming and todays level is around 0,075 K.
I wonder if the peoble creating the 350 ppm demonstrations knows this?
I wonder how they will react when they find out.