In 2012, an incredibly important milestone may have passed on climate change, and none of us noticed. That year may have been when the world reached peak carbon dioxide emissions per person. If so, that would mark a key inflection point in the world’s collective efforts to dramatically decarbonize the global economy.

Global population is expected to continue to increase through the century, from about 7.8 billion people in 2020 to about 10.9 billion in 2100, according to the central estimate of the United Nations. That means that the only way for carbon dioxide emissions to be reduced will be to reduce the amount emitted per person, since we won’t be reducing the number of people like in the 1976 sci-fi film Logan’s Run.

Let’s look at some data. The figure below shows global per capita carbon dioxide emissions from fossil fuels and industry for the period 1979 to 2040. From 1970 to 2018 are observations, using data from the International Energy Agency (IEA) on emissions and the United Nations on population.  For the period 2019 through 2040 the graph shows per capita emissions for two scenarios. The red line shows emissions under the IEA Current Policies Scenario (CPS) which projects “how global energy markets would evolve if governments make no changes to their existing policies and measures.” The green line shows emissions under the IEA Stated Policies Scenario (SPS) which “reflects the impact of existing policy frameworks and today’s announced policy intentions.”

Under the Current Polices Scenario global per capita carbon dioxide emissions do not exceed the 2012 peak until the late 2030s. Under the Stated Policies Scenario, global per capita carbon dioxide emissions steadily decline to 2040. If governments follow through on their existing commitments – never guaranteed – or even partially meet those commitments, then the world is now past peak per capita carbon dioxide emissions.  

Some caveats. Scenarios are not predictions. They are “what if” exercises based on a wide range of assumptions. The world could evolve in many ways tha diverge from even the most current and updated scenarios.

For instance, in contrast to the near-term scenarios of the IEA, most of the baseline scenarios of the Intergovernmental Panel on Climate Change Fifth Assessment Report project significant increases in per capita carbon dioxide emissions to 2040. More than 90% of the AR5 baseline scenarios project 2040 per capita emissions that are higher than the IEA Current Policies Scenario, and almost 98% are higher than the IEA Stated Policies Scenario — that is only 5 of more than 240 scenarios.

The large differences between projections based on IEA and those of the IPCC should motivate reflection and reconsideration by the climate research and policy communities. Consider that per capita emissions today are a bit less than 4.8 tonnes per person, and for 2040 the two IEA scenarios suggest values of ~4.2 tonnes (SPS) and ~5.0 tonnes (CPS). In contrast, almost 60% of IPCC AR5 references scenarios exceed 6.0 tonnes per person, and they top out at greater than 9 tonnes per person. The shorter term energy outlook of the IEA (along with other short-term energy outlooks) is not consistent with the most recent work of the IPCC, and the research that it relies upon. It remains to be seen if the forthcoming Sixth assessment report of the IPCC will address these issues.

So has the world passed peak per capita carbon dioxide emissions?  Prediction, as Niels Bohr may or may not have said, is really difficult — especially about the future.

However, on current trends, and based on the most up-to-date scenarios for the next few decades, it appears that there is indeed a very good chance that the world has passed peak per capita carbon dioxide emissions. And we didn’t even notice it.

Passing peak per capita carbon dioxide emissions does not make the challenge of deep decarbonization any easier – the challenge remains mindbogglingly huge. But it does mean that there is a bit more wind at our back, and that should provide some welcome optimism on a topic more often characterized by gloom and doom.



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