I developed a model of Global Warming based on the anthropogenic perturbation of the Carbon Cycle. The essence of this model is a rate equation for the evolution of the carbon dioxide (CO2) concentration in the atmosphere.
The interesting results from this model are projected trends for the CO2 concentration and the average global temperature during the next century. The character of those trends — whether rapid rises, shallow plateaus, or diminishment into the future — depend crucially on the magnitude of our civilization’s emissions of CO2, and whether those anthropogenic emissions increase or decrease with time. In the real world at present, they are increasing.
I have now been able to include the effect of linearly increasing or decreasing anthropogenic emissions into my Carbon Balance Model, which has been significantly improved.
This model also includes the effect of the increase in the rate at which atmospheric CO2 is absorbed by photosynthesis and the surface waters of the oceans, because those absorption rates are increasingly stimulated by the higher levels of CO2 in the air. This process of absorption-enhancement cannot continue indefinitely as the atmospheric CO2 concentration increases, but at what point of elevated CO2 concentration it saturates and then absorption largely shuts down, is unknown.
The third process included in the model is that of the slow absorption of atmospheric CO2 by the chemical reactions of weathering on the surfaces of rocks and soils. CO2 not “quickly” scavenged from the air by photosynthesis or the surface waters of the oceans will stay airborne for 12,000 to 14,000 years. The ~2,500ppm spike of atmospheric CO2 that occurred 55.5 million years ago took 200,000 years to clear away. That geological episode is known as the Paleocene-Eocene Thermal Maximum (PETM). At that time there was no ice at the poles, instead they were jungles and swamps with crocodiles. The global temperature at the peak of the PETM was as much as +12°C to +18°C warmer than in our pre-industrial 18th century.
I made three case studies from this model, called E-growth, E-flat, and E-fall.
The E-growth case is driven by a relentlessly steady rise of anthropogenic CO2 emissions, based on the average upward trend of those emissions between years 1960 and 2020.
This trend arrives at 470ppm of atmospheric CO2, and a warming of +1.5°C (above pre-industrialization), in the year 2038 (in 18 years). It arrives 540ppm and +2°C in year 2055 (in 35 years); and it arrives at 800ppm and +4°C in year 2100 (in 80 years).
The E-flat case is driven by a constant annual rate of 42.2GtCO2/y of anthropogenic emissions (42.2 giga-metric-tons of CO2 emissions per year), which is the rate in year 2020.
It arrives at 470ppm and +1.5°C in year 2041 (in 21 years); and 540ppm and +2°C in year 2070 (in 50 years); and 600ppm and +2.5°C in year 2100 (in 80 years).
The E-fall case is driven by a steady linear reduction of anthropogenic emissions over 40 years: from 42.2GtCO2/y in 2020, to 0GtCO2/y in 2060; a reduction of 1.05GtCO2 every year for 40 years. This amount of annual reduction is 2.5% of the total anthropogenic emissions in year 2020. In this scenario, after year 2060 we would continue our civilization with zero CO2 emissions from our human activities.
This trend rises to 437ppm and +1.23°C during years 2035 to 2040 (from 15 to 20 years in the future) after which both fall. It arrives back down to 407ppm and +1°C in year 2059 (in 39 years); and 320ppm and +0.4°C in year 2100 (in 80 years).
In this year of 2020, we are presently at 417ppm and +1.08°C.
The math and physics details of this new work, as well as graphs of the trends calculated from it, are shown in the report (PDF file) linked at
A Carbon Balance Model of Atmospheric CO2
11 September 2020