Some commenters on my previous blog post, Net Zero CO2 Emissions: A Ruin and Totally Unnecessary, were skeptical of my claim that nature would continue to remove CO2 from the atmosphere at the same rate even if anthropogenic emissions were to drop…suddenly eliminated.
Instead of appealing to a simple CO2 budget model I made for a blog post, let’s look at the published data from 123 (!) IPCC authors rely on to provide the best estimate of CO2 flows in and out of the atmosphere, the Global Carbon Project Team. I created the chart below from the data spreadsheet available here. Updated annually, the 2023 report shows that the best estimate of the net removal of CO2 from the atmosphere by land and ocean processes is increasing along with the increase in atmospheric CO2. This plot is from annual estimates, 1850-2022.
The two regression lines that fit the data are important, because they show what will happen in the future as CO2 in the atmosphere continues to rise. In the case of nonlinear fit, which has a slightly better fit to the data (R2 = 89.3% vs. 88.8%), the carbon cycle is slightly less able to remove excess CO2 from the atmosphere. This is what carbon cycle modelers hope will happen, and there is some weak evidence that it is starting to happen. So, let’s conservatively assume that a nonlinear removal rate (a gradual decrease in nature’s ability to absorb excess atmospheric CO2) will occur in the coming decades as a function of atmospheric CO2 content.
Modest CO2 Reduction Scenario
Now, let’s assume a 1% annual reduction in emissions (both fossil fuel burning and deforestation) in each year starting in 2024. That 1% annual cut is nowhere near the Net Zero target of eliminating CO2 emissions by 2050 or 2060, which at this point it seems illusory because humans remain dependent on fossil fuels. The resulting trajectory of future atmospheric CO2 looks like this:
This suggests that a modest cut in global CO2 emissions (33% by 2063) would result in stable CO2 concentrations for about 40 years, with a peak CO2 value of 460 ppm. This is only 2/3 of the way to “2XCO2” (double the estimated pre-Industrial CO2 level).
How Much Global Warming Will Be Caused In This Scenario?
Assuming all atmospheric CO2 increases are due to human activity, and further assuming all climate warming is due to CO2 increases, the final equilibrium warming (delayed by the time required for mixing to warm the deep oceans) would be about 1.2. deg.C considers the value of Effective Climate Sensitivity (EffCS) based on observations of 1.9 deg. C that was published last year (Spencer & Christy, 2023). Using the value of Lewis and Curry (2018) around 1.6-1.7 deg. C will lead to less warming in the future.
And if there is no emission reduction of more than 33% of emissions vs. 2023. If the 1% reduction per year continues through the 2060s, as shown in graph 2 above, the CO2 content in the atmosphere will then decrease, and future warming will not will respond to 460 ppm, which can only be reached briefly in the early 2060s. This would be a value lower than 1.2 degrees. C. Note that this is below 1.5 deg. C maximum warming target of the 2015 Paris Agreement, which is the basis for the Net Zero policy.
Net Zero is based on a Wrong View of Nature
Net Zero assumes that human emissions of CO2 must stop to prevent an increase in atmospheric CO2. This is false. The first plot above shows that nature is removing atmospheric CO2 at a rate based on the atmospheric CO2 content, and as long as it remains elevated, nature continues to remove CO2 at a rapid rate. “Global Greening” observed by satellites is evidence of land. Above the ocean, seawater absorbs CO2 from the atmosphere in proportion to the difference in CO2 partial pressure between the atmosphere and the ocean, that is, the higher the atmospheric CO2 content, the faster the ocean absorbs CO2.
Neither the land nor the oceans “know” how much CO2 they emit in any given year. They only “know” how much CO2 is in the atmosphere.
All that is required to stop the rise of atmospheric CO2 is for annual anthropogenic emissions to be reduced to match the annual rate of removal by nature. Data from the Global Carbon Project shows that the reduction is about 33% below the emissions of 2023. And it is based on the conservative assumption that the removal of CO2 in the future will follow a nonlinear curve in the first plot, above, rather than a linear relationship.
Finally, 1.5 deg. The C maximum warming target of the 2015 Paris Agreement would be easily met under the scenario proposed here, a global net emission cut of 1% per year (fossil fuel burning plus land use change), for a total of 33% emission reduction vs. 2023 in the early 2060s.
I continue to be confused as to why Net Zero is a goal, as it is not based on science. I can only assume that the scientific community is silent on the matter because politically motivated energy policy goals are driving science, rather vice versa.
