The richest tenth of the world's people produce half of all carbon emissions, while the poorest half - most threatened by droughts and super storms linked to climate change - produce only one tenth, Oxfam said on Wednesday.
The richest 10 percent have, on average, carbon footprints 11 times that of the poorest 3.5 billion people on the planet, the campaign group said in a report to coincide with talks in Paris this month on a global deal to slow climate change.
One of the biggest obstacles facing negotiators from 195 countries is how to find the billions of dollars needed by developing nations to enable them to stop using fossil fuels and adapt to severe weather shocks caused by climate change.
"Climate change and economic inequality are inextricably linked and together pose one of the greatest challenges of the 21st century," Tim Gore, Oxfam's head of food and climate policy, said in a statement.
"Paris must be the start of building a more human economy for all - not just for the 'haves', the richest and highest emitters, but also the 'have-nots', the poorest people who are the least responsible for and most vulnerable to climate change."
Emissions are rising fastest in developing countries, Oxfam said.
Yet emissions relating to goods and services consumed by the richest citizens in China, India, Brazil and South Africa remain some way behind those of their counterparts in the wealthiest countries of the Organization for Economic Co-operation and Development (OECD), it said.
Oxfam found that India's richest 10 percent use on average just one quarter of the carbon used by the poorest half of the population of the United States.
It also said the total emissions of China's poorest 600 million people - half the country's population - are only one third of the total emissions of the United States' richest 10 percent, some 30 million people.
"Rich, high emitters should be held accountable for their emissions, no matter where they live," Gore said.
"But it's easy to forget that rapidly developing economies are also home to the majority of the world's very poorest people and while they have to do their fair share, it is rich countries that should still lead the way."
Oxfam said a select group of billionaires, who had made many of their fortunes in fossil fuels, were the only people to stand to gain from a weak deal in Paris.
Experts say the world's poorest, regardless of the country they are living in, are often the least prepared in terms of coping with the effects of climate change, and women, especially in rural areas, are the most vulnerable.
A deal in Paris would be by far the strongest ever agreed to bind rich and poor nations to limit greenhouse gas emissions, which scientists say have blanketed the earth, raised global temperatures and begun upending the planet's climate system.
"Any deal must keep alive the possibility of holding global warming at 1.5 degrees Celsius, and provide a major boost in funding to help the poorest and most vulnerable communities adapt to climate change," Gore said.
So far, pledges made by 184 countries to curb greenhouse gas emissions beyond 2020, made in the run-up to the Paris summit, are too weak to limit the rise in global temperatures to 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times.
That is widely viewed as a threshold for dangerous and potentially catastrophic changes in the planet's climate system.