Peak Carbon Dioxide Emissions and Peak Carbon Dioxide Concentration

David P. Turner / December 2, 2020

A remarkable speculation is now circulating in the cybersphere to the effect that global emissions of carbon dioxide (CO2) from fossil fuel combustion may have peaked in 2019.  Considering that recent formal projections generally indicate increasing emissions through 2030 or longer, this assertion is striking.  It matters because CO2 emissions determine the growth in the atmospheric CO2 concentration, which in turn influences the magnitude of global warming.

The atmospheric CO2 concentration is currently 415 ppm (up from a preindustrial value of around 280 ppm) and is rising at a rate of 2-3 ppm per year.  The consensus among climate scientists is that rapid greenhouse-gas-driven climate change will be harmful to the human enterprise on Earth.  It would be good news indeed if CO2 emissions were on the way down.

Estimates for annual global CO2 emissions are produced by assembling data on consumption of coal, oil, and natural gas, as well as data on production of cement, which also releases CO2 (the sum is termed Fossil Fuel & Industry emissions).  Deforestation is another significant anthropogenic source of CO2, but it is not considered in this blog post except to say that reducing deforestation will further reduce total CO2 emissions.

The suggestion that we are passing peak fossil fuel emissions is based on several observations.

1.  The rate of increase in global emissions has been low in recent years, averaging less than 1% per year for 2010-2018.  CO2 emissions are falling in the US and the EU, and the annual rate of increase in emissions is declining in India

Covid-19 related reductions in global fossil fuel consumption for 2020 will be 7% or more.  Emissions will likely rebound to some degree as the pandemic recedes but perhaps not fully.

2.  Peak global coal use likely occurred in 2013.  Aging coal powered electricity plants in the U.S. are often replaced with plants powered by natural gas (more efficient that coal) or renewable energy.  Some coal plants are being prematurely retired.  A gradual phase out in global coal consumption will be driven by the price advantage of renewable energy, impacts of coal emissions on human health, and the reluctance of insurance companies to cover new coal power plant construction.

3.  Peak oil use may have occurred in 2019.  Global demand in 2020 will fall about 10% because of Covid-19.  Structural changes such as reduced commuting and business-related flying mean that some of the demand reductions will be persistent.  Vehicles powered by electricity and hydrogen rather than gasoline are on the ascendancy, sparked in part by governmental mandates to phase in zero emissions vehicles.

4.  Even a near term peak in natural gas consumption is being discussed.  Again, the price advantage of renewable sources will increasingly weigh against fossil-fuel-based power plants.  Ramped up production of renewable natural gas could substitute for fossil natural gas in some applications.

Surprisingly, it appears likely that a long-term decline in total fossil fuel use will be driven more by lack of demand than lack of supply.

Emissions from cement manufacturing are still climbing and amount to about 4% of total fossil fuel emissions.  However, a recent study suggests that the CO2 uptake from slow weathering of aging cement around the world is providing a large offset (more than half) to current cement manufacturing emissions.  Innovative uses of wood and geopolymers can potentially replace cement in many construction applications.

The election of Biden to the U.S. presidency is also relevant.  Biden’s leadership will return the U.S. (largest cumulative CO2 emissions on the planet) to the international fold with respect to climate change mitigation.  President Xi Jinping of China (largest CO2 emitter on the planet) has also displayed leadership (in words if not deeds) on the climate change issue.  A revitalized collaboration between the U.S. and China on climate change mitigation could push the needle on global emissions reduction.

Currently about half of fossil fuel CO2 emissions remain in the atmosphere, with the remainder sequestered on the land (e.g. in vegetation and soil) and in the ocean.  Once fossil fuel emissions begin decreasing and fall by half − and assuming the net effect of increasing CO2 and climate warming is still substantial carbon uptake by the land and ocean − the atmospheric CO2 concentration will peak and begin to decrease.  The year of peak CO2 concentration could be as early as 2040 (see carbon cycle projection tool below).

There is of course plenty that might go wrong.  The net effect on the land and ocean sequestration just referred to could be a decline in carbon uptake.  On land, carbon sources such as permafrost melting and forest fires will be stimulated by climate warming.  In the ocean, warming will intensify stratification, thereby reducing carbon removal to the ocean interior. 

On the other hand, land sequestration is increasing now and could continue to do so in response to CO2 enhancement of photosynthesis and plant water use efficiency.  Policy driven increases in the land carbon sink (e.g. more reforestation and afforestation) are also possible.  The ocean carbon sink is likewise increasing now, continuing an upward trend over the last 20 years.

Whatever specific years do turn out to be peak CO2 emissions and peak CO2 concentration, they will be remembered as historic hallmarks in humanity’s effort to address an existential threat of its own making.

Recommended:  Interactive CO2 Emissions and Concentration Projection Tool.