The countries most responsible for global warming owe the rest of the world a tremendous debt, with the author of a new study published Monday in the journal Nature Climate Change putting the figure at $10 trillion.

The author came up with that number by calculating how much CO2 each country emitted per capita since 1960, generally recognized as the onset of the worst of human-caused global warming. Countries with high per capita emissions carry a carbon debt while countries with lower per capita emissions have a carbon credit.

“We in the rich world have over-contributed to the problem and consequently there is a debt associated with that that needs to be honored in some way,” said lead author Damon Matthews a researcher at Concordia University in Montreal, Canada.

That was the purpose of the Green Climate Fund, established in 2010 by the United Nations Framework Convention on Climate Change (UNFCCC) to help vulnerable countries address the challenges of climate change. Its initial goal was to distribute $100 billion each year in public and private funding until 2020. So far wealthy nations have pledged $10.2 billion, a fraction of the debt, according to the new study.

The United States is responsible for about 40 percent of the debt.

The study concludes  the carbon debt of high-emitting countries totals 250 billion metric tons of carbon dioxide since 1990. The U.S. government calculates the social cost of CO2 emissions –including property damage from increased flooding, reduced agricultural productivity and adverse effects on human health– is about $40 per metric ton of CO2.

Multiplying the two figures  produces the $10 trillion figure.

Others, however, say Matthews’ accounting may be overly simplistic. According to Jan Fuglestvedt research director of the Center for International Climate and Environmental Research in Oslo, Norway, the dates chosen to calculate the debt are arbitrary. Emissions since 1960 account for about 66 percent of CO2 emissions since  the start of the industrial era in 1750; emissions since 1990 are 36 percent.

Counting earlier emissions could change the debts owed by different countries, although Fuglestvedt admitted deciding when to start counting is more of a policy choice than a scientific one.

“When should we know and when should we start counting the emissions that change climate?” Fuglestvedt asked. “That goes beyond natural sciences.”

Another issue with the study is counting emissions only by country, said Liane Schalatek, who has attended Green Climate Fund board meetings on behalf of the Heinrich Böll Foundation North America, where she is associate director.  

“The biggest polluters in absolute terms are not necessarily countries but entities within countries, that is very often large corporations,” Schalatek said. “If you put their pollution together [they] actually make up the majority of the pollution.”

A 2013 study funded in part by the Böll Foundation found nearly two-thirds of carbon dioxide emitted since the 1750s can be traced to the 90 largest fossil fuel and cement producers, most of which are still operating. 

Although the Green Climate Fund does not address corporate responsibility, Schalatek said it is time to stop haggling about where this money will come from and time to start giving larger sums. 

“They should really just say 100 billion is the minimum and we should be thinking about how we can scale that up post 2020,” Schalatek said.

Karen Orenstein, an international policy analyst for Friends of the Earth, said, however, that studies like this don’t address the real reason the carbon debt exists.

“A lot of this isn’t really about what science says or academics say,” Orenstein said. “It’s political.”