Looking at something else and finding myself here:

https://judithcurry.com/2014/08/24/the-50-50-argument/

I decided to try to reconcile two things from the IPCC.

Sensitivity:

“Likely > 66% probability”

“the ECS is likely between 1.5°C and 4.5°C” – IPCC

Attribution:

“Extremely likely > 95% probability”

“It is *extremely likely* that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.” – IPCC

With sensitivity we have X to 3X with 66% certainty.

With attribution we have roughly Y to 2Y with 95% certainty.

The question is, does sensitivity drive attribution? As you can see the range seems to tighten as we move to attribution. 66% says to me we could be wrong. 95% says we’re right. It’s at the financial audit level of confidence.

What if we do this? Take their attribution as a given. Now work backwards to determine sensitivity. The Sensitivity numbers might tighten up.

I will try to do this using simple math.

1950 assumed to be CO2 310 ppm.

2010 pretty close CO2 385 ppm.

A 24% increase.

From an IPCC chart, the increase in C was about 0.5 C.

From the attribution statement, we caused from 0.25 C to 0.50 C temperature rise. I rounded away from 51% and 99%.

So we may have, half of what happened, 0.25 C to all of it, 0.50 C from a 24% increase. Rounding to a doubling of a 100% increase, we just multiply by 4. So we may have 1.0 C to 2.0 C for a doubling of CO2.

I have attempted to use the attribution of the IPCC to drive the sensitivity value. I decided to use what they are more certain about to shed light on what they are less certain about. I’ve used simple math. 4 times 24% may not equal 96% or 100%. I have some concerns about a log scale.

http://www.climatechange2013.org/images/figures/WGI_AR5_FigSPM-1.jpg

http://pmel.noaa.gov/co2/files/co2_data_mlo.jpg