A new analysis lays out which countries are responsible for climate change by looking at a full accounting of both current and historical emissions.

“The question of who is responsible for using up the carbon budget is clearly crucial in the context of climate justice debates,” writes Carbon Brief. “It speaks to the responsibility for dealing with the impact of climate change to date—as well as who ought to do the most to prevent further warming.”

But “assigning responsibility is far from straightforward,” the UK-based publication adds.

The amount of CO2 released since the industrial revolution is directly correlated with rising temperatures on the planet surface. But targeting the biggest annual emitters—led by China, followed by the U.S., Russia, Brazil, and Indonesia—to implement the most ambitious emission reduction plans overlooks several key data areas, a gap that many countries and stakeholders say undermines fairness.

For instance, although China’s annual emissions today far outpace any other nation, the country’s high population means its per capita emission rate is only half that of the second-biggest annual emitter, the United States. But while that contrast is often suggested as reason to shift responsibility to high per capita emitters, Carbon Brief finds that cumulative per capita measurements are not directly related to warming.

Other metrics, like historical emissions, paint a much more accurate picture of climate accountability. As China is fond of stating, nations industrializing over the past half-century are following 200 years of industrialization in countries like the U.S. and the United Kingdom. Industrialized countries are therefore responsible for more emissions than is indicated by present-day rates, and thanks to CO2’s long-lasting warming effect, the elapsed time does not diminish their impact.

China’s leaders argue that industrialized countries should bear the brunt of climate action, and claim that industrializing countries have a right “to do what Western countries have done in the past, releasing carbon dioxide in the process of developing [their countries’] economy and reducing poverty,” says BBC. 

Measuring historical accountability is difficult because of questionable data and shifting national boundaries. However, the exercise does offer insight into the main issue of how to develop a plan for global climate action. Furthermore, historical accountability provides an opportunity to address the emissions driven by the colonizing policies of countries like the U.S., the Soviet Union, and United Kingdom, which amassed wealth through expansion. “Although these countries have significantly reduced their emissions in recent decades, they remain among the most important contributors to historical warming today,” Carbon Brief writes.

“In the U.S., for example, a wave of settlers spread across the continent from east to west, following their ‘manifest destiny’ and clearing land for farming as they went.” Other countries showing notably high emissions from colonization-driven deforestation include New Zealand, Gabon, Malaysia, the Republic of Congo, and some South American nations.

“In terms of assigning ‘responsibility’ for these emissions, this again raises difficult questions relating to colonization and the extraction of natural resources by foreign settlers,” says Carbon Brief.

Climate accountability should also consider disparities in production and trade, with some governments importing carbon-intensive products from other nations that might then be held accountable for the emissions they produce.

“Consumption-based emissions accounts give full responsibility to those that use the products and services rendered with fossil energy, tending to reduce the total for major exporters, such as China,” Carbon Brief explains. But again, history complicates the issue. Not only are there few accurate emissions data for global trade before 1990, countries also played different exporting or importing roles in the past. Although China is now seen as the world’s “workhouse,” for example, a century ago that status was held by Britain and Germany.

Accounting for all of these factors, Carbon Brief’s analysis has the United States ranking highest for national responsibility: “The U.S. has released more than 509 Gt CO2 since 1850 and is responsible for the largest share of historical emissions,” amounting to some 20% of the global total.” China is a “relatively distant second,” followed by Russia, Brazil, and Indonesia. Post-colonial European nations account for 3% and 4% of the global total, “not including overseas emissions under colonial rule.”

Carbon Brief’s analysis is based on territorial CO2 emissions and considers the impact of emissions imported or exported by global production and trade. Though evaluating the ranking relative to population alters some countries’ emission responsibility—notably China and India, which fall lower on the list—“per capita rankings depend strongly on the methodology used and—unlike cumulative emissions, overall—these figures do not relate directly to warming.”

The analysis is based on information starting from 1850 and only considers CO2 emissions, not other greenhouse gases or aerosols.