WARSAW – One question, now that the world's climate scientists have definitively declared that humanity has triggered global warming, is what to do with the United Nations agency established to assess the robustness of climate science?

A group of 130 developing countries, headed by Brazil, has an answer: Instruct the Intergovernmental Panel on Climate Change to investigate historic emissions.

In their thinking, apportionment of past emissions would bring clarity to just who's responsible for fixing the mess that's brought the world to the brink of climate chaos.

Not surprisingly, given that developed countries in Europe and North America have for nearly 200 years used the atmosphere as a dumping ground while they built their economies, the idea has gone nowhere here at the climate talks in Warsaw.

 "The entire discussion was blocked," said Brazil's chief negotiator, Ambassador José Marcondes de Carvalho. "These are interesting ideas.... Why not have a discussion in an open and transparent manner?"

The debate hits one of the most divisive issues at these global talks – the notion of "emissions space."

The atmosphere can take only so much extra carbon before impacts become serious. Where that exact line is remains uncertain, but scientists are fairly confident it's somewhere below an atmospheric carbon dioxide concentration of 500 parts per million. Some say it's as low as 350 ppm.

The problem: Pre-industrial concentrations were about 287 ppm, and we're already at 400 ppm, with hundreds of millions of people in the developing world still without electricity or modern energy. One line of thinking at the UN talks is that the developed world has used its allotment of emissions space; it must leave room for the rest of the world to catch up.

A number of graphics attempt to show this. Dutch blogger Lars Boelen, using data from the Carbon Dioxide Analysis Center and the International Energy Agency, made a chart showing just how much of the "carbon pie" each generation has consumed.

Another graphic, circulated on Twitter by German broadcaster Deutsch Welle, shows how different cumulative, historic emissions look from the current scenario: China three years ago surpassed the United States as the global greenhouse gas emissions leader. But the country is not that different from Russia, the UK and Germany on the historic scale.

That's changing fast, however. And that's one reason the developed world doesn't want to get "distracted" by a discussion of past emissions: Much of the world's greenhouse emissions growth in the future is coming from the China, India and other rapidly developing countries.

"The focus is somewhat misplaced," said Todd Stern, the United States' chief negotiator, at a press conference Monday. "The notion of responsibility has got to be based on historic emissions, absolutely, current emissions and future emissions that you lock in with infrastructure that you're building."

Energy use – and associated fossil-fuel emissions – in the developed world has largely plateaued. Meanwhile analysts expect China's energy use to be double the United States' by 2040.

Where does this leave the IPCC?

Kevin Trenberth, a senior analyst at the National Center for Atmospheric Research and a longtime IPCC participant, sees little but pitfalls.

First, the IPCC charter is to assess the body of science on climate change. "To assess means it has to exist somewhere, preferably published," he said via email.

Not all the carbon dioxide emitted historically remains in the atmosphere, either, he added. "So just doing this inventory, were it possible, would still not be fair." Plus a considerable slice of that inventory is difficult, if not impossible, to measure, such as burning wood for fires.

There's also the question of when to start the tally. Some suggest 1750. Others wait until 1850. Looking across all energy sources, Trenberth said, the main increase in emissions came after 1960.

Finally, there's a question of population. "The energy problem is very much a per capita one," he said. "So how is the 'blame' allocated: by country, [or] by country per capita?"

Those, Trenberth concluded, "are probably political considerations, although some science and objectivity can be brought to bear."

"In any case it is not the IPCC."

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.