If you live in the US or Australia, then between 1990 and 2013 you accumulated a debt of more than U$12,000. People in the UK are doing a bit better, racking up about US$4000 in debt over that time.

This isn’t about overspending on credit cards, but about damage done to our atmosphere. If we think of the atmosphere as a limited resource to be shared equally by all, then those who pollute more than their fair share – that is, more than the global average – can be said to be in “emissions debt”. Conversely, those who pollute less are in “emissions credit”.

Damon Matthews from Concordia University in Montreal, Canada, adopted this view of the atmosphere and calculated how every country stands.

He found that the US, for example, had over-polluted by a massive 100.3 billion tonnes of carbon dioxide between 1990 and 2013 – amounting to 300 tonnes per person. That’s about as much as is produced by driving a family car from Los Angeles to New York and back about 150 times.

And according to the US Environmental Protection Agency, each tonne of carbon dioxide produced today has a social cost of about $40, so the overall debt per person is US$12,000.

Creditors

The developing nations pollute less than the global average and so end up as creditors. For example, on average each of India’s 1.2 billion people has accumulated an emissions credit of 63 tonnes, worth US$2500.

China, too, is a creditor – to the tune of 8.5 billion tonnes of CO2 – but has started to eat into that as it now emits more carbon dioxide per head of population than the global average.

Matthews got broadly similar results for the US, UK and China when he carried out a separate analysis including other greenhouse gases and the impact of land-use changes such as deforestation. He also expressed the debts and credits in terms of each country’s contribution to global warming.

According to Matthews, 1990 was chosen as the starting point partly because this was when global emissions figures started to become widely available. It was also roughly when the science of climate change became well established enough that it began to make sense to talk of responsibility and accountability, he says.

In the run-up to the UN climate summit in Paris, these sorts of calculations take on new significance.

Owning up

“It is important to acknowledge and own up to how much we in the developed world have over-contributed to historical climate changes,” Matthews says. He says the numbers could be used as a starting point to decide how much rich nations should contribute to the Green Climate Fund, used to help poor nations adapt to climate change.

But will the climate negotiators pay any notice?

“Having followed the negotiations for 20 years I can tell you now the parties will not accept a neat allocation of responsibility based on this kind of metric, although I think this is one of the fairest,” says Robyn Eckersley at the University of Melbourne, Australia.

Eckersley says each country pushes for a particular metric that downplays their own responsibility. But that doesn’t make the analysis pointless, she adds.

“They help society look more critically at what each country is doing and how they are hiding behind their cherry-picked metrics. That’s a really useful function,” she says. “These kinds of documents make it easier for people to judge contributions and raise these issues at a national level.”