Dr. Matthew Wielicki Attempts Math

Today I came across a post on X from Dr. Matthew Wielicki in which he claims that warming from 1916 - 1942 was the same amount as from 1998 - 2024. Both time periods show +0.6°C warming. Since CO2 was lower and "more stable," Wielicki claims that "This one chart delivers a devastating blow to the core climate narrative, that recent warming is both unprecedented and primarily caused by human CO₂ emissions." Here's the chart he shared.

There are times when I'm simply amazed at the level of stupidity coming from contrarian influencers, especially among those that certainly know better. His own bio on X says, "Dr. Matthew Wielicki stands as a beacon of rational thought. With a Ph.D. in earth science from UCLA and as a professor-in-exile, he bravely challenges the norms that many in the scientific community only whisper about." So Wielicki is claiming to have the expertise to offer rational criticism of the norms of within climate science. How did he do?

If you look carefully at Wielicki's graph, you'll see that he simply chose two sets of two annual anomalies 26 years apart and subtracted the earlier year from the later year. But anyone with a Ph.D. in earth science from UCLA knows this is not how you compare trends. Natural variability affects beginning and ending years, so simply subtracting two numbers doesn't give an accurate picture of the amount of warming took place. This is blatant cherry-picking. Instead, Wielicki should have calculated the trends for each 27-year interval. And as a general rule, he should have compared two 30-year (or longer) time intervals, but let's let that slide for now. Let's do some math correctly and see if Wielicki's claim has any integrity. 

On NOAA's website where Wielicki got his graph, there's a tool that allows you to display NOAA's calculated trends between any two years. So I chose 1916 - 1942 and this is the graph NOAA showed me.

I then chose 1998 to 2024 and this is the graph that NOAA showed me.

Just using the tools available to Wielicki on NOAA's site shows that warming occurred at 0.16°C/decade for 1916 - 1942 and 0.24°C/decade for 1998 - 2024. In other words, NOAA shows warming occurring about 50% faster for 1998 - 2024 than for 1916 - 1942. Dr. Wielicki could easily have done this and discovered that his claim is dead wrong. Let's go a step further; I downloaded NOAA's data and calculated the trends myself with 2σ confidence intervals. Here are my results. They agree with NOAA's.

    1916 - 1942: 0.157 ± 0.042°C/decade (2σ) 

    1998 - 2024: 0.244 ± 0.053°C/decade (2σ) 

So warming from 1998 -2024 was ~55% faster than 1916-1942. Since each of these intervals are technically 27 years we can estimate the amount of warming for each time interval:

    1916 - 1942: 0.157 °C/decade * 2.7 decades = 0.42°C

    1998 - 2024: 0.244 °C/decade * 2.7 decades = 0.66°C

So Wielicki is wrong, and anyone with a Ph.D. in earth science should be able to articulate exactly why he's wrong. More importantly, Dr. Wielicki has presented no evidence challenging that human activity (GHGs + aerosol pollution) is responsible for ~100% of the warming above the 1850-1900 mean. 

But let's look a little more closely at 1916 - 1942. Is a value of 0.42°C consistent with what we'd expect? Over shorter periods of time, other factors may well be at play. Let's do some back of the envelope calculations:

• CO2 Forcings: CO2 increased from 302 ppm to 311 ppm from 1916 - 1942, so RF = 5.35*ln(311/302) = 0.16 W/m^2. If TCR is near 2 C, then CO2 alone is responsible only for 0.1°C.
• Solar Forcings: Using Kopp's TSI data, I calculated in increase of ~0.15 W/m^2 (large uncertainty) for 1916 - 1942. That would add about another 0.1°C. While solar forcings added to the trend between 1916 - 1942, they subtract from the trend from 1998 - 2024.
• Data Biases & Uncertainties: Uncertainties are somewhat larger during WWII (for obvious reasons), and significant study has been put into resolving biases introduced due to changes in sample collection methods in the late 19th and early 20th centuries. These biases are not fully resolved, and I discuss these here and here. It's possible that warming rates were slightly less from 1916 - 1942 than the data currently suggests.
• Natural Variability: Using 27 years doesn't eliminate all sources of natural variability.

Furthermore, Gillett's analysis[1] examined how well CMIP6 models reproduced historic warming, and while the1940s nearly reached the end of the 95% confidence envelope for CMIP6, it's still inside the envelope.

So the warming trend from 1916 - 1942 does appear to be within the expected range, at least as far as CMIP6 is concerned. Furthermore, a quantitative analysis of natural vs anthropogenic forcings since 1850 is consistent with human activity being responsible for virtually all warming above the 1850-1900 mean, even if natural forcings add variability on shorter time scales. The best case scenario is that Dr. Wielicki didn't do his homework on this and failed to be a "beacon of rational thought" in this discussion.

References:

[1] Gillett, N.P., Kirchmeier-Young, M., Ribes, A. et al. Constraining human contributions to observed warming since the pre-industrial period. Nat. Clim. Chang. 11, 207–212 (2021). https://doi.org/10.1038/s41558-020-00965-9