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.

What Technosphere Response to Covid-19 Says About Earth System Dynamics

David P. Turner / November 8, 2020

In the discipline of Earth System Science, a useful analytic approach to sorting out parts and wholes is by reference to the earthly spheres.  The pre-human Earth system included the geosphere, atmosphere, hydrosphere, and biosphere.  With the biological and cultural evolution of humans came the technosphere.  In a very aggregated way of thinking, these spheres interact.

The biosphere is the sum of all living organisms on Earth; it is mostly powered by solar radiation and it drives the biogeochemical cycling of elements like carbon, nitrogen, and phosphorus.

The technosphere is the sum of the human enterprise on Earth, including all of our physical constructions and institutions; it is mostly powered by fossil fuels and it has a large throughput of energy and materials.

Over the last couple of centuries, the technosphere has expanded massively.  It is altering the biosphere (the sixth mass extinction) and the global biogeochemical cycles (e.g. the CO2 emissions that drive climate change).

The interaction of the technosphere and the biosphere is evident at places like wildlife markets where captured wild animals are sold for human consumption.  Virologists believe that such an environment is favorable to the transfer of viruses from non-human animals to humans.  The SARS-CoV-2 virus likely jumped from another species, possibly wild-caught bats, to humans in a market environment.  Covid-19 (the pandemic) has now spread globally and killed over one million people.

The human part of the technosphere has attempted to stop SARS-CoV-2 transmission by restricting physical interactions among people.  The summed effect of these self-defense policies has been a slowing of technosphere metabolism.  Notably, Covid-19 inspired slowdowns and shutdowns have driven a reduction in CO2 emissions from fossil fuel combustion and a decrease in the demand for oil.  This change is of course quite relevant to another interaction within the Earth system − namely technosphere impacts on the global climate.

The reduction in CO2 emissions in response to Covid-19. Image Credit: Global Carbon Project.

There are important lessons to be learned from technosphere response to Covid-19 about relationships among the Earthly spheres.

One lesson regards the degree to which the technosphere is autonomous.

If we view the technosphere as a natural product of cosmic evolution, then the increase in order that the technosphere brings to the Earth system has a momentum somewhat independent of human volition.  The technosphere thrives on energy throughput, and humans are compelled to maintain or increase energy flow.  It is debatable if we control the technosphere or it controls us.

In an alternative view, tracing back to Russian biogeochemist Vladimir Vernadsky in the 1920s, humanity controls the technosphere and can shape it to manage the Earth system.  This view received a recent update with a vision of Gaia 2.0 in which the human component manages the technosphere to be sustainably integrated with the rest of the Earth system.

The fact that humanity did, in effect, reduce technosphere metabolism in response to Covid-19 supports this alternative view. 

Admittedly, the intention in fighting Covid-19 was not to address the global climate change issue.  And the modest drop in global carbon emissions will have only a small impact on the increasing CO2 concentration, which is what actually controls global warming.  Nevertheless, the result shows that it is possible for human will to affect the whole Earth system relatively quickly.  The Montreal Protocol to protect stratospheric ozone is more directly germane. 

A globally coordinated effort to reduce greenhouse gas emissions is clearly possible.  It could conceivably be accomplished without the painful job losses associated with Covid-19 suppression if done by way of a renewable energy revolution that creates millions of infrastructure jobs.

A second lesson from technosphere reaction to Covid-19 is that a technosphere slowdown was accomplished as the summation of policies and decisions made at the national scale or lower (e.g. slowdowns/shutdowns by states and cities, and voluntary homestay by individuals).  The current approach to addressing global climate change is the Paris Agreement, which similarly functions by way of summation.  Each nation voluntarily defines its own contribution to emissions reduction, and follow-up policies to support those commitments are made at multiple levels of governance.  This bottom-up approach may prove more effective than the top-down approach in the unsuccessful Kyoto Protocol. 

A third lesson from technosphere response to Covid-19 regards the coming immunization campaign to combat it.  Many, if not most, people around the planet will need to get vaccinated to achieve widespread herd immunity.  Success in addressing the climate change issue by controlling greenhouse gas emissions will likewise depend on near universal support at the scale of individuals. Education at all levels and media attention are helping generate support for climate change mitigation.  Increasing numbers of people are personally experiencing extreme weather events and associated disturbances like wildfire and floods, which also opens minds.  The political will to address climate change is in its ascendency. 

The response of the technosphere to biosphere pushback in the form of Covid-19 shows that the technosphere has some capacity to self-regulate (i.e. to be tamed from within).  Optimally, that capability can be applied to ramp up a renewable energy revolution and slow Earth system momentum towards a Hothouse World.