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Concentrated, cumulative, global and historical CO2 emissions – do they all matter the same?

“Never waste a good crisis”. Is It possible to find something positive in being confined due to COVID-19? Apparently yes, since the confinement of world populations has resulted in a decrease of CO2 emissions by 6.4 % or 2.3 billion tonnes in 2020. The decline is significant, approximately twice Japan’s yearly CO2 emissions – but what emissions reduction are we talking about and is it really good news?

1. Current, concentration and cumulative CO2 emissions

Unlike current emissions of CO2 which refer to the flow of released emissions in the atmosphere at a given time cumulative CO2 emissions is the total sum of all CO2 emissions over time. For example, since 1751, the world has emitted over 1.5 trillion tonnes of CO2

The cumulative nature CO2 emissions derives from the extensive residence time of fossil carbon in the atmosphere, biosphere, and ocean. It is estimated that once it is added to the atmosphere CO2 gas can hang between 300 to 1,000 years.

CO2 concentration is linked to cumulative emissions. It describes the amount of gas by volume in the air as parts per million (ppm). The global average atmospheric carbon dioxide in May 2020 was 417 ppm.

It is the level of CO2 concentration in the atmosphere which determines the extent of the global warming effect. Put differently, it is the cumulative effect of past emissions – the stock of CO2 that matters the most rather than the flow.

COVID-19 has had no measurable impact on CO2 emissions concentration and cumulative CO2 emissions. its impact on global warming is therefore quasi null.

2. Ambitious or ambiguous emission targets?

While there is a consensus on reducing CO2 emissions, there has been a tendency to stylize the debate as current emissions vs. cumulative emissions at the legal, policy, judicial, scientific and financial levels bringing ambiguity.

2.1 Policy level

i) Current emissions

"Recognizing the urgency to go further to tackle climate change" The UK Government revealed an "ambitious new climate target" to reduce GHG emissions by at least 68% compared to 1990. The reduction applies to newly released CO2 emissions.


ii) Cumulative emissions

Most Climate Vulnerable Forum countries address the issue of responsibility by highlighting their insignificant contribution to cumulative greenhouse gas emissions in their NDCs and calling on large historical emitters to both reduce emissions and financially support adaptation in CVF countries.

2.2 Judicial level

i) Current emissions

The lawsuit, The Netherlands vs. Urgenda, established Netherland’s inadequate action on climate change. The court imposed a legally binding target and deadline for a government to reduce its GHG emissions, by at least 25 % from 1990 levels by the end of 2020.

ii) Cumulative emissions

The ruling of the famous investigation conducted by the Commission on Human Rights of the Philippines against the 47 carbon majors reads found them liable for cumulative emissions Based on various evidence including Richard Heede’s report.

2.3 Scientific level

i) Current emissions

The classic renewable energy sources, solar and wind technologies, prevent a substantial CO2 emission, by contributing more and more of the world energy demand.

ii) Cumulative emissions

To achieve net CO2 emissions, it is necessary to sink carbon which means extract some carbon dioxide out of the atmosphere and or ocean. Technologies are developed to suck CO2 from the air called direct air capture. It uses either adsorption where CO2 sticks to a surface or chemical reactions which capture CO2. This technology is now patented.

2.4 Finance level

i) Current emissions

A carbon tax directly establishes a price on current emissions. There is no upper limit on the volume emissions that companies can generate. Carbon tax increase may deter CO2 emitters on long term.

ii) Cumulative emissions

The EU ETS, as a cap-and-trade system, issues a set number of emissions allowances yearly. This upper limit considers different factors including the cumulative emissions and their likely impact on global warming. The price on the EU ETS is currently 39.09, surpassing a point last reached in 2006 shortly after the scheme launched.

The EU ETS increasing market price of recently emitted CO2 tonnes seems to echo the inherent risks of cumulative CO2 emissions on the planet. However, this should not undermine the fact that today’s CO2 emissions aren’t less harmful than the cheaper ones traded on the EU ETS market 10 years ago, which equally contribute to global warming due to their aggregation.

3. Looking ahead

GHG emissions continue to concentrate and accumulate. The reduction of CO2 emissions generated in 2020 by 6.4 % due to the pandemic won’t stop this trajectory. The climate system is based on significant accumulations or reductions of emissions over a long period of time. Such correlational reasoning does not hold with one-year decrease of CO2 emissions. Stakeholders and policy makers should better explain the inextricable link between current and cumulative emissions and allow people to distinguish them as well.


By Fabrice Mattei

© 2021


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