Who is responsible for climate breakdown? This question has triggered heated debate for several decades now, as the politicians of powerful countries jockey to shift blame and avoid liability for the catastrophic damages that are now cascading around us.

But for all the hand-waving, the question of responsibility is in fact quite simple to answer – at least at the level of nation-states. To do it, we need to calculate the extent to which each country’s cumulative historical emissions have overshot their fair share of the “planetary boundary”, which scientists have defined as 350 parts per million (ppm) concentration of CO2 in the atmosphere. This boundary was crossed in the late 1980s, and it is possible to identify which countries are most responsible for the excess emissions that are presently causing climate breakdown.

I took this approach in a paper published recently in the journal Lancet Planetary Health, and the results are quite striking. The historical record shows that the United States is single-handedly responsible for 40 percent of excess global CO2 emissions. The European Union and the United Kingdom are together responsible for 29 percent. And along with the rest of Europe, Canada, Australia, New Zealand, Israel and Japan, the Global North as a group is collectively responsible for no less than 92 percent.

Meanwhile, the Global South – the entire continents of Asia, Africa and Latin America – are responsible for only 8 percent of excess emissions. And that’s from only a handful of countries, such as around the Gulf. The majority of countries in the Global South still remain within their fair shares of the planetary boundary, including large nations like India, Indonesia and Nigeria. Even China was within its fair share as of 2015, the final year of data in this study, although it has since overshot the limit.

Social movements in the Global South have long argued that we should understand climate breakdown as a process of atmospheric colonisation. And they are correct. The atmosphere is a shared commons, on which all of us depend for our existence. Just as powerful countries enriched themselves by appropriating land, labour and resources from the South during the colonial period, so too they have appropriated the atmospheric commons, with devastating consequences for all of life on Earth.

Social movements in the Global South have long argued that we should understand climate breakdown as a process of atmospheric colonisation.

To make matters worse, the impacts of climate breakdown fall disproportionately on the countries of the Global South, which suffer the vast majority of climate change-induced damages and mortality within their borders, and where extreme weather is already causing crop failure, food insecurity, and mass displacement. Research on climate vulnerability at the University of Notre Dame finds that developing countries are significantly more at risk than their richer counterparts in virtually every category for which we have data.

The disparities here are stark. If you look at a map showing countries by emissions overshoot alongside a map showing countries by climate vulnerability, you’ll see that the two are almost exact inversions of each other. In other words, not only does climate breakdown represent processes of atmospheric colonisation, but the consequences are playing out along colonial lines. And those who have done the least to cause this crisis are suffering the most. It would be difficult to overstate the scale of this injustice. If we are not attentive to the colonial dimensions of climate breakdown, then we are missing the point.

There is a straightforward case for reparations here. And these results can be used as a guide when it comes to adjudicating liability for climate damages. Overshooting countries should be held liable for the costs of climate-related damages, wherever they occur, in proportion to their responsibility for total excess emissions. This would mean that “undershoot” countries – those that still remain within their fair share of the planetary boundary – would receive reparations for the suffering they endure.

Climate negotiators from the Global South have long called for a system to deal with loss and damage, while the leaders of rich countries have repeatedly refused. The politics of this question are clearly fraught, but the good news is that there is no technical barrier to climate reparations because the governments of the main overshooting countries have the power to issue hard currencies, like the dollar and the euro. Transfers could be made at the stroke of a keyboard.

Of course, the approach I have described here cannot capture everything. Using nation-states as the unit of analysis obscures inequalities of responsibility within countries. As recent reports have highlighted, richer individuals have much higher lifestyle emissions than everyone else. And we should also pay attention to the fossil fuel companies, as well as corporations that control supply chains and provisioning systems, which involve emissions over which ordinary citizens have little control.

To the extent that national governments are responsible for national policy, and to the extent that they are the relevant parties in the climate negotiations, a nation-state focus makes sense. But clearly, the responsibility for reparations should fall on the wealthy ruling classes who have benefitted most from the existing economic system.

As a guide for the future, the only obvious implication is that the overshooting countries have a clear moral responsibility to end their emissions faster than the global average rate.

This is not to say that we don’t need all hands on deck when it comes to climate mitigation. We do. All countries must decarbonise as quickly as they can manage. The results I have described here simply describe responsibility for excess emissions and climate damages. As a guide for the future, the only obvious implication is that the overshooting countries have a clear moral responsibility to end their emissions faster than the global average rate – a principle that is indicated in the Paris Agreement as “common but differentiated responsibility” – as well as to assist other countries to decarbonize through technology transfers and other forms of support.

As climate damages continue to worsen, the question of responsibility will only heat up. We need to have a clear-eyed view of this problem – one rooted in the principles of atmospheric commons and climate justice.