Responding to the CO2 Coalition's "Fact #5" on Acceleration of CO2 Emissions

The CO2 Coalition's Fact #5 is titled, "CO2 emissions began accelerating in the mid-20th century." This one doesn't even get its title superficially correct. The explanation that goes with this is rather short, so I'll share it all. "Global man-made CO2 emissions began accelerating in the post-World War II economic boom and continue increasing today. If CO2 is the primary factor driving a warming planet, we should see indications of an acceleration of warming beginning in that period and continuing today." The graph associated with this "fact" is below.

There are at least two obvious problems with this. First, you can detect acceleration in emissions by an upward curve - that indicates that emission rates are increasing. Clearly this curve is present in the late 19th century, then flattens early 20th century and increases again in the 1930s or so. But second, and more importantly, the CO2 Coalition did not show any emissions from land use change. Below is a graph I made from the 2023 Global Carbon Budget showing CO2 emissions from land use change exceeding emissions from fossil fuels and industry up through the end of WWII.

But rather than just eyeballing the above graph, I decided to calculate running 10 year slopes for human carbon emissions in GtC/year. If there's an upward slope in this graph we can detect acceleration in CO2 emissions. While emission rates go up and down (largely due to land use changes), the overall trend is towards increasing emission rates since the late 19th century. The good news here is that emission rates have flattened in the last decade or so.

And I think we should evaluate the CO2 Coalition's claim that "If CO2 is the primary factor driving a warming planet, we should see indications of an acceleration of warming beginning in that period and continuing today." In point of fact, the CO2 coalition already admitted in their "fact #2" that there's a logarithmic relationship between CO2 concentrations and temperature. And if you plot CO2 as radiative forcing on the x-axis and GMST changes on the y-axis, you get a very good correlation between CO2 and temperature.

Studies also show that GMST should increase linearly with cumulative carbon emissions, regardless of RCP scenario, and this is also observed in the data for cumulative emissions., regardless of RCP scenario. The slope of this relationship 1.83 ± 0.099°C/TtC (2σ).

It turns out that if you evaluate the actual anthropogenic carbon emission rates and compare these to the increase in temperature, it shows very clearly that this data is consistent with the fact that "CO2 is the primary factor driving a warming planet."