Temperature over time
Figure 1: The average surface temperature of the world's oceans, using the baseline of 1971 to 2000 average. The shaded band shows the range of uncertainty in the data based on the number of measurements collected and the precision of the measurements used. Source: EPA.
Figure 1 shows the rise of the surface temperature of the oceans during the industrial age. Now, if we look at the protection against climate change as a "control loop," the measurement of that loop is that temperature, which has increased by only about 1.5 °C during the past century, and today we're just beginning to see its consequences (melting ice, wildfires, hurricanes). This rate of rise is still slow (2.0-3.0 °C per century) but is accelerating. My estimate is it will reach a rise of about 5.0 °C by 2075. In my view, we'll never stopat 2.0°C (recommended by the Paris Agreement of 2015) and particularly not at 1.5 °C (recommended by the U.N. Intergovernmental Panel on Climate Change – IPCC in 2018) because this high-inertia process is totally out of control.
Some believe that because the numbers describing the temperature rise are small, the problem we face is also small. This is not the case. Let me compare them with our own body temperature, which is accurately controlled by our brain. The body temperature of a healthy, resting adult human being is 98.6 °F (37.0 °C). Our "thermostat" (called the hypothalamus, a portion of the brain) controls body temperature. The span of our thermostat is 36.4–37.1 °C (97.5–98.8 °F) or about 0.7 °C. This thermostat turns on shivering at 97.5 °F and initiates sweating at 98.8 °F. I mention this only to illustrate that certain processes must be controlled within small limits because small temperature changes can have large effects.
According to all scientific data, the thermostat of global temperature control is CO2 concentration in the atmosphere. If it rises, the global temperature rises (because the thermal insulation of the planet increases), and when it drops, the planet cools.
During the past 1 million years, nature "controlled" this concentration by keeping the inflow of CO2 into the atmosphere (generated by animal life and man) roughly equal the outflow (intake of plants and dissipation by the oceans), and therefore the atmospheric concentration of CO2 stayed roughly constant, never exceeding 280 ppm even during ice ages, changing sun spot numbers, volcanic activity or meteor impacts.
If we look at the atmosphere as a tank and CO2 concentration as the level in that tank, then we could say that this level stayed reasonably constant for a million years because it never exceeded 280 ppm (the planet didn't need to start "sweating") as nature took care of it. Since the beginning of the industrial revolution, humans gradually took over this control from nature, CO2 concentration in the atmosphere increased from 280 to more than 410 ppm, and it's predicted by most models that it will reach or even exceed 500 ppm by the end of this century.
If a control engineer was to bring this process under control by returning CO2 concentration to the stable, pre-industrial state, the task would be to balance the in and outflows of this tank, and on top of that, remove roughly half of the CO2 that accumulated during the industrial age. If a conventional level controller was installed on this tank, it would see an error of 410 – 280 = 130 ppm and a past error accumulation of some 400-500 Gt (gigatons) of carbon. It would immediately close the inlet valve and open the outlet valve.
Unfortunately, in this process, these valves are stuck. The outflow from the tank (the CO2 intake of the plants and dissipation by the oceans) can’t be increased. In fact, it has probably decreased during the past century because of deforestation, acidification of the oceans, and building of dams/reservoirs, holding 8,000 km3 of water, which also emit carbon to the atmosphere. In short, this outlet valve is almost completely stuck, and we have no technology to open it further except reforestation, which is unlikely due to overpopulation (during the industrial age, population increased from 1.0 to 9.0 billion).
