If the current best guess for climate sensitivity is 3.0 degrees C ( The increase in GMST for doubling of CO2 from 280 ppm to 560ppm)

Country member energy policies lead to stablilistaion at 650 ppm what would the de facto temperature target be ?
given that members accepted a 2.0 degree increase as its target in 1997

Can only think of

90 ppm is increase between 560ppm and 650 ppm

3.0 oC/280 p.p.m x 90 p.p.m = 0.964 oC or 1.0 oC ( to - one decimal place)

So 2 oc + 1 Degree = 3 oC

Anyone check this out for me ...

Many thanks

You worked it correctly IF THE MODEL IS LINEAR.

In reality, I am not certain the model should be linear.

Model is linear .. rough back of envelope calculations only required to complete this question thank you for your help and comments

To determine the de facto temperature target given the information provided, we can calculate the temperature increase associated with the additional 90 ppm of CO2.

First, we need to calculate the temperature sensitivity per ppm of CO2, based on the given climate sensitivity of 3.0 degrees Celsius for a doubling of CO2 from 280 ppm to 560 ppm.

Temperature sensitivity per ppm of CO2 = (3.0 degrees Celsius) / (560 ppm - 280 ppm)

= 3.0 degrees Celsius / 280 ppm

= 0.0107 degrees Celsius per ppm

Next, we multiply the temperature sensitivity per ppm of CO2 by the increase in CO2 concentration (90 ppm) to find the temperature increase associated with it.

Temperature increase = (0.0107 degrees Celsius per ppm) * (90 ppm)

= 0.963 degrees Celsius

Rounding to one decimal place, the temperature increase associated with the additional 90 ppm of CO2 would be approximately 1.0 degrees Celsius.

Since the members accepted a 2.0-degree increase as their target in 1997, we add this to the calculated temperature increase.

De facto temperature target = 2.0 degrees Celsius + 1.0 degrees Celsius

= 3.0 degrees Celsius.

Therefore, the de facto temperature target would be 3.0 degrees Celsius.

Please note that this calculation is based on the given information and assumptions about climate sensitivity and CO2 concentrations.