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Possible Future Trends of CO2 Concentration and Global Temperature

Wildfire smoke and power line, northern California. Photo: Jeffrey St. Clair.

Carbon dioxide gas (CO2) has been accumulating in the atmosphere since the dawn of the Industrial Revolution (~1750), because increasingly voluminous fluxes of that gas have been exhausted from the lands and the oceans, and are beyond the capacity of natural CO2 sinks to absorb completely.

Prior to the Industrial Revolution, carbon would cycle through a variety of processes that sustained the continuation of life, death, evolution and rebirth, and that all meshed into one grand balance. That balance is called the Carbon Cycle.

The explosive growth of human activity, numbers, exosomatic power, economic wealth, military overkill, and hubristic political pretensions, all spring from the access to and profligate use of heat-energy liberated from fossil fuels. Carbon dioxide is the exhaust fume from our Promethean exertions for greater conquests — and wealth.

The carbon dioxide exhausted by our civilization’s generation of heat-energy, and from our massive exploitation of once virgin land areas, is an increasingly destabilizing perturbation of the Carbon Cycle. This perturbation is called Anthropogenic Emissions.

The imbalance of the Carbon Cycle reverberates through the natural world in many ways that are increasingly harmful and dangerous to Planet Earth’s habitability for ourselves and for many other animal and plant species. The central reality of this complex of growing threats to the viability of the Biosphere is called Global Warming.

Carbon dioxide gas traps heat radiated towards space, as infrared radiation from the surface of Planet Earth, reducing our planet’s ability to regulate its temperature by cooling to compensate for the influx of solar light that is absorbed by the lands and the oceans, and stored by them as heat.

Because of the existential implications of runaway global warming — as well as the intrinsic fascination to curious minds of such a richly complex and grand human-entwined natural phenomenon — scientists have been studying global warming, and its impact on the biosphere, which called Climate Change.

While scientists of all kinds are excited to share their findings on climate change and impress their colleagues with their new insights, members of the public are singularly interested to know how climate change will affect their personal futures. Can science offer them clear and reliable answers to their questions — and fears — and provide practical remedies and technological inoculations to ward off the threats by climate change to our existing ways of life?

Science does what it can to offer practical insights and helpful recommendations, and humanity does what it usually does when faced with a collective existential crisis: it hides from the inconvenience of drastically changing its personal attitudes and societal structures, which is in fact the only way it would be able to navigate the majority of Earth’s people through the transition to a new social paradigm; a new, sustainable and harmonious relationship between human life and Planet Earth.

While I am grateful to all the professional climate scientists — and their related life scientists who study many aspects of this complex of geophysical processes and biological organisms and systems — for making known so much of the workings of the globally warming biosphere, I am nevertheless curious to gain a quantitative understanding of it all for myself. To that end, I have devised my own phenomenological thermodynamic “toy models” of global warming. The sequence of my reports charting the evolution of my quantitative understanding of global warming, are listed here [1].

My newest report describes a rate equation for the accumulation or loss of atmospheric CO2 over the course of future time. This equation is derived from considerations of recent data on the Carbon Cycle (from the Global Climate Project), along with some mathematical assumptions about the relationships used to quantify “carbon dioxide sweepers,” the processes that scavenge atmospheric CO2.

The results of this work are projections of possible future histories of the concentration of atmospheric carbon dioxide, as well as a projection of the most likely trend of rising average global temperature.

The complete report on the new work (of which this is just a brief summary) is available here [2].

As is true of all future-casts, we will just have to wait till then to see if they were accurate, assuming we don’t do anything beforehand — collectively — to avoid the worst possibilities.

Such is the dance with the chaos and nonlinearity of the approaching future.

From the general mathematical result of this model, three possible future trends of CO2 concentration history were calculated:

CASE #1, “business as usual,” anthropogenic emissions continue at today’s level indefinitely;

CASE #2, anthropogenic emissions are immediately reduced to the point of holding CO2 concentration constant at today’s level, indefinitely;

CASE #3, anthropogenic emissions are immediately reduced to a trickle, so as to reduce the excess of CO2 in the atmosphere as quickly as possible.

Also, the trend of rising global temperature that accompanies CASE #1 was calculated.

CASE #1 is a pure growth trend, from 407.4ppm to 1040.7ppm over the course of about 300 years (ppm = parts per million of concentration in the atmosphere).

CASE #2 requires that the anthropogenic emission rate be ~50% of the current rate (or 21GtCO2/y instead of 41GtCO2/y; for the units GtCO2/y defined as giga-metric-tonnes of CO2 emission per year).

This reduced rate of anthropogenic emission would just keep the CO2 concentration at 407.4ppm (from the beginning of 2019) into the near distant future (~300 years, and beyond), during which time the excess heat-energy presently in the biosphere would continue to degrade our weather, climate, environments, biodiversity, and planetary habitability.

CASE #3 would clear away the current excess of CO2 in the atmosphere, and then continue to reduce the atmospheric CO2 concentration to a very low level over the course of about 300 years. This would require that anthropogenic emissions be immediately reduced to less than one-fifth (1/5) of their current levels, and maintained at or below that level indefinitely.

The implication is clear: if we wish to reduce the amount of CO2 in the atmosphere we have to reduce our anthropogenic emissions well below 50% of what they are today, maintain that discipline indefinitely, and wait centuries to millennia to achieve a significant reduction.

The global temperature excursion (above the average global temperature of the pre-industrial world) that accompanies CASE #1 rises steadily, though at a diminishing rate, from +1°C in 2019, to nearly +5.8°C in 2300 (~300 years). Along the way it passes +1.5°C in year 2027.3 (in ~7 years), and it passes +2°C in year 2036.5 (in ~17 years).

If the +1.5°C and +2°C temperature rise milestones are truly to be avoided then it is imperative that anthropogenic emissions be drastically reduced immediately. As yet there is no sign that such reductions will occur.

The physics and mathematics of all this are fascinating, but the implications for civilization and life-on-Earth are stark.


[1] One Year of Global Warming Reports by MG,Jr

15 July 2020


Updated to 7 September 2020

[2] A Rate Equation for Accumulation or Loss of Atmospheric CO2

5 September 2020


Manuel Garcia Jr, once a physicist, is now a lazy househusband who writes out his analyses of physical or societal problems or interactions. He can be reached at mangogarcia@att.net