Among the stumbling blocks for a global climate deal in Paris is a decades-old U.N. view that divides the world into two camps -- wealthy countries that bear the financial responsibility for climate change and developing nations that do not.
From the outset, one of the biggest issues has been moving money from those rich nations that have produced most of the world's greenhouse gas emissions since the industrial revolution to developing nations that want funds to help shift their growing economies to a lower-carbon future.
But the breakdown stems from 1992 when countries agreed on the United Nations Framework Convention on Climate Change -- and much has changed over the past two and a bit decades, including the rapid rise of Asian economies.
Back then, China was one-third its current economic size and it has seen its greenhouse gas emissions grow almost three-fold between 1990 and today, according to the International Energy Agency.
And until the past year or so, a prolonged energy boom bolstered exporting nations in the Gulf.
As a result, a re-reckoning is in order, richer nations argue. They want a new climate agreement in Paris to recognize a more diverse pool of climate finance "donor countries" who will contribute to the goal of raising $100 billion a year by 2020 and more in the years beyond to help developing nations grow and cope with the effects of climate change.
"The whole notion of what defines developing countries is hamhanded and artificial," said Paul Bledsoe, a former energy and climate aide to former U.S. President Bill Clinton.
Romania vs Saudi
One European Union source said it was unfair that a nation like Romania, ranked 52 in per capita wealth this year and with a GDP 8 times its size in 1992, has to pay when Saudi Arabia, ranked ninth, one notch below the United States, does not.
Not a chance, say many of those who have climbed up the rich list since 1992.
"Let me be very clear about it: Climate finance is a pure role for the annex one countries," said Energy Minister Sultan Ahmed Al Jaber of the United Arab Emirates, referring to the countries on the rich list.
The UAE is now ranked as the world's fifth-richest nation on a per capita basis by the World Bank.
"We would like to see developed countries fulfill their pledges to provide funds and to support the various mechanisms for tech transfer, adaptation and capacity building. All of this has been agreed over the past few years."
Seven of the 10 richest countries measured in GDP per capita identified by the World Bank are considered developing countries in the United Nations climate negotiations and would not have an obligation to provide climate aid to poorer countries.
Negotiators from 195 countries are trying to agree an accord in Paris to slow climate change by steering the global economy away from its ever-growing reliance on fossil fuels. They have until Friday to come up with an accord.
The negotiators are wrestling with how to revise the issue of "differentiation" between rich and poor countries, which not only hampers discussions around climate finance but other aspects of a potential deal.
While the UAE and China, among others, have made voluntary contributions toward financing cleaner energy in some of the world's poorer nations, they reject the idea of being required to contribute toward the $100 billion goal.
The UAE through its renewable energy assistance program has financed renewable energy projects from solar in Fiji and Afghanistan to a mini hydroelectric project in Argentina, Al Jaber says.