Uncertain Uncertainties
17 hours ago
Guest Post by Willis Eschenbach
Well, I’ve been thinking for a while about how to explain what I think is wrong with how climate trend uncertainties are often calculated. Let me give it a shot.
Here, from a post at the CarbonBrief website, is an example of some trends and their claimed associated uncertainties. The uncertainties (95% confidence intervals in this instance) are indicated by the black “whisker bars” that extend below and above each data point.
Figure 1. Some observational and model temperature trends with their associated uncertainties.
To verify that I understand the graph, here is my own calculation of the Berkeley Earth trend and uncertainty.
Figure 2. My own calculation of the Berkeley Earth trend and uncertainty (95% confidence interval), from the Berkeley Earth data. Model data is taken directly from the ClimateBrief graphic.
So far, so good, I’ve replicated their Berkeley Earth results.
And how are that trend and the uncertainty calculated? It’s done mathematically using a method called “linear regression”. Below are the results of a linear regression, using the computer program R.
Figure 3. Berkeley Earth surface air temperature, with seasonal anomalies removed. The black/yellow line is the linear regression trend.
The trend is shown as the “Estimate” of the change in time listed as “time(tser)” in years, and the uncertainty per year is the “Std. Error” of the change in time.
This gives us an annual temperature trend of 0.18°C per decade (shown in the “Coefficients” as 1.809E-2 °C per year), with an associated decadal uncertainty of ±0.004°C per decade (shown as 3.895E-4°C per year)
So … what’s not to like?
https://wattsupwiththat.com/2023/06/26/uncertain-uncertainties/
