David P. Turner / January 11, 2024 (update)

Figure 1.  Projections of CO₂ emissions and concentration.  Image Credit NOAA

In 2020, a remarkable speculation circulated 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 indicated increasing emissions through 2030 or longer, this assertion was 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 around 420 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 and effects of land use.  The sum of fossil fuel and cement emissions is termed Fossil Fuel & Industry emissions (FF&I).  Land use, land use change, and forestry (LULUCF) is mostly the net effect of carbon emissions from deforestation and carbon sequestration from afforestation/reforestation.  Total anthropogenic emissions are the net of FF&I and LULUCF.  Two independent estimates of CO2 sources and sinks (GCP and IEA) differ slightly.

The suggestion that peak fossil fuel emissions occurred in 2019 held true in 2020 and again in 2021 and 2022, but 2023 saw a 1.1% increase over 2019. 

Intriguingly, a decline in LULUCF compensated for the increase in fossil emissions such that total anthropogenic emissions remained the same in 2023 as 2022 (11.1 GtC yr^-1).  That result may hold in 2024 as well if President Lula of Brazil continues to succeed in reducing deforestation, and global fossil fuel emissions grow only modestly (if at all).

Several specific observations points towards lower emissions in the near-term future.

1.  Global coal emissions declined from 2012 to 2019 but have risen above 2012 in recent years, primarily due to increases in India and China.  However, coal emissions declined 18.3% in the USA and  18.8% in the EU in 2023.  Aging coal powered electricity plants in the U.S. are being replaced with plants powered by natural gas (more efficient that coal) or renewable energy.  Some coal plants have been prematurely retired.  A gradual phase out in global coal consumption is being 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.  China has agreed to stop financing the construction of coal power plants in developing nations and India has pledged to stop approving new domestic coal plants.

2.  Peak oil use may have occurred in 2019.  Global demand in 2020 fell 7.6% because of Covid-19. It partially recovered in 2021 and 2022 and 2023 but remains below the level in 2019.  Structural changes such as reduced commuting and business-related flying mean that some of the demand reductions associated with Covid-19 have persisted.  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.

3.  Even a near-term peak in natural gas consumption is being discussed.  The GCP budget for 2022 showed a 0.2% decline in gas emissions and for 2023 a 0.5% increase.  Again, the price advantage of renewable sources will increasingly weigh against fossil-fuel-based power plants.  The growing importance of energy security at the national level also argues against dependence on imported fossil fuels.  Ramped up production of renewable natural gas could substitute for fossil natural gas in some applications.

It is likely that the approaching peak in total fossil fuel use will be driven by diminishment of demand rather than lack of supply.

Currently about half of FF&Iemissions remain in the atmosphere, with the remainder sequestered on the land (e.g. in vegetation and soil) and in the ocean.  The land sink is increasing in response to 1) high CO₂ enhancement of photosynthesis and plant water use efficiency, and 2) policy driven impacts on land management (e.g. more reforestation and afforestation).

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).

On the other hand, there is plenty that might go wrong with this optimistic scenario.  As climate change intensifies, the net effect on land and ocean sequestration 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.  The steady increase in the ocean carbon sink since around 2000 has stalled in recent years, for poorly understood reasons.  If fossil fuel emissions are not significantly abated in the coming decades, the CO₂ concentration could still be rising in 2100 (Figure 1).

Recommended:  Interactive CO₂ Emissions and Concentration Projection Tool.