For over a year now, climate activists have been publishing different prescriptions on how to avoid dangerous temperature rises. They now have carbon budgets to avoid going over 2C, they have an organization dedicated to keeping CO2 concentrations under 350 ppm and they have Representative Concentration Pathways that show some of what they think will happen as we increase our forcings. But they have entirely skipped over several key steps needed for their prescriptions to be credible.
They are like college kids trying to make rabbit stew for the first time. However, they have neglected the key step–first, catch the rabbit.
We don’t know if any carbon budget is accurate because we don’t know what the sensitivity of the atmosphere is to a doubling of CO2 concentrations.
These are ‘finger in the wind’ exercises based on the mid-point estimate of 3C sensitivity. But the range of sensitivity values is 1.5C to 4.5C and all of the estimates derived from recent studies indicate it is likely to be far closer to the lower end of that range than the mid-point.
For those busy making carbon budgets etc., it seems as though time stopped in 2009, six years ago.
It would be relatively easy to make carbon budgets on a sliding scale that would say, “If sensitivity is X then our carbon budget is Y.” The fact that nobody has done so clearly emphasizes the point that these are exercises in communication, not science.
In that, these carbon budgets resemble the 2C target and the 350 ppm goal. They are established not based on any scientific study but rather from a desire to draw a line in the sand. Which is understandable, right up to the point when science tells us that those lines in the sand were wrongly drawn and are incorrect.
There is nothing really wrong with rabbit stew without the rabbit. It just has a different name.