Quantifying national excess CO2 emissions

The following extract is from an important study published 1 September 2020 by the highly respected medical journal, The Lancet.

The article provides a key to understanding the response to reducing global carbon emissions in terms of environmental justice. It details a method for quantifying national responsibility for damages related to climate change by looking at national contributions to cumulative CO2 emissions in excess of the planetary boundary of 350 ppm atmospheric CO2 concentration.

This approach is rooted in the principle of equal per capita access to atmospheric commons. For this analysis, national fair shares of a safe global carbon budget consistent with the planetary boundary of 350 ppm were derived.

These fair shares were then subtracted from countries’ actual historical emissions (i.e. territorial emissions from 1850 to 1969, and consumption-based emissions from 1970 to 2015) to determine the extent to which each country has overshot or undershot its fair share. Through this approach, each country’s share of responsibility for global emissions in excess of the planetary boundary was calculated.

Study Findings

A summary of the study’s findings show that as of 2015:

  • the USA was responsible for 40% of excess global CO2 emissions;
  • the European Union+UK (EU-28) was responsible for 29% of excess global CO2 emissions
  • the industrialised countries (i.e. those classified by the UN Framework Convention on Climate Change as Annex I nations were responsible for 90% of excess emissions global CO2 emissions;
  • the Global North ( i.e. USA, Canada, Europe, Israel, Australia, New Zealand, and Japan) was responsible for 92% of excess emissions global CO2 emissions;
  • By contrast, most countries in the Global South (Latin America, Africa, the Middle East, and Asia) were within their boundary fair shares, including India and China.

These figures show that high-income countries have a greater degree of responsibility for climate damages than previous methods have implied. These results offer a just framework for attributing national responsibility for excess emissions, and a guide for determining national liability for damages related to climate change, consistent with the principles of planetary boundaries and equal access to atmospheric commons.


The UN Framework Convention on Climate Change (UNFCCC) includes the principle of “common but differentiated responsibilities and respective capabilities”. This principle has been widely used to determine differential national responsibilities for mitigation efforts. But the principle of differentiated responsibilities can also be applied to allocating responsibility for climate change itself, and damages related to climate change, on the grounds that countries that have contributed more to global emissions are more responsible for related problems than those that have contributed less. The present analysis offers a novel method for doing so, in a manner that is consistent with the principles of planetary boundaries and equal access to atmospheric commons.

A. For the purposes of this analysis, the term Global North refers to the USA, Canada, Europe,
Israel, Australia, New Zealand, and Japan, whereas the term Global South refers to the rest of
the world: Latin America, Africa, the Middle East, and Asia.

B. The parties to the United Nations Framework Convention on Climate Change (UNFCCC)
are divided into groups. Annex I parties are industrialized nations and countries with economies
in transition. Annex II parties are the Annex I countries but not the countries with economies in transition.
Non-Annex I parties are mainly developing nations. 

There are various existing approaches to measuring national responsibility for climate change. Negotiations and agreements under the UNFCCC are focused on current territorial emissions (i.e. country output). Based on this approach, China’s responsibility is more than double that of the USA, and India comes just behind the European Union (EU-28; table 1).

When it comes to climate change, however, what matters is stocks of CO2 in the atmosphere, not annual flows; so responsibility must be measured in terms of each country’s contribution to cumulative historical emissions.12 Using 1850 as the base year, the USA and the EU-28 are about twice as responsible as China, whereas India is responsible for only a small fraction of historical emissions (table 2). 

Looking at countries’ historical emissions alone is not adequate, however, given the differences in population size. For instance, China might have contributed substantially to cumulative emissions (although only half of the emissions of each of the US and the EU+UK), but it also has a much larger population than other countries (eg, it is about four times the size of the USA). Any metric of responsibility should ideally take this discrepancy into account4  We can expect that doing so would show the national responsibility of the USA to be proportionally higher than suggested in table 2, whereas China’s responsibility would be proportionally lower.

One way to approach this is to start from the principle that the atmosphere is a shared and finite resource, and that all people are entitled to an equal share of it

Building on this principle, we can measure national responsibility for climate damages by looking at the extent to which nations have exceeded or overshot their fair share of a given safe global emissions budget. Such an approach would allow us to calculate national responsibility for emissions in excess of the global budget in a manner that takes account of both scale and population. Countries that have exceeded their fair share would then be said to owe a climate debt to countries that have remained within their fair share.

Based on the results in table 5 it can be seen that the USA has contributed 40% of total national overshoot emissions. This same ratio can be used to determine the extent of national responsibility for emissions in excess of the global planetary boundary, and therefore for climate breakdown. The USA is therefore responsible for 40% of climate breakdown. The USA and the EU-28 together are responsible for 69% (Figure A). The G8 countries (the USA, EU-28, Russia, Japan, and Canada) are together responsible for 85%.

Source: The Lancet Planetary Health,  Volume 4, Issue 9, E399-E404, Sept 01, 2020 Open Access
DOI: https://doi.org/10.1016/S2542-5196(20)30196-0

The full Lancet study with Tables etc is available at this link:

Author: Dr Jason Hickel, Goldsmiths College, University of London, UK.

Dr Hickel is an economic anthropologist and a Fellow of the Royal Society of Arts.  He is Professor at the Institute for Environmental Science and Technology at the Autonomous University of Barcelona, and Visiting Senior Fellow at the International Inequalities Institute at the London School of Economics. He is Associate Editor of the journal World Development, and serves on the Statistical Advisory Panel for the UN Human Development Report, the advisory board of the Green New Deal for Europe, and the Harvard-Lancet Commission on Reparations and Redistributive Justice.