Rancorous negotiations over a draft version of a universal climate treaty took place this week in Bonn, Germany. The treaty is supposed to be adopted by nearly 200 nations at the U.N. Climate Change Conference in Paris in December. The fight in Bonn is over how much the countries of the world should cut their emissions of greenhouse gases, by what year they should complete those cuts, and who should pay for the transition.

For example, some proposed provisions of the draft treaty would require the complete decarbonization of the global economy by 2050 and the transfer of more than $100 billion per year from rich countries to poor countries after 2020. The funds are supposed to compensate poor countries for climate change damages and to pay for their adoption of no-carbon energy sources.

What would it take to achieve total energy decarbonization? To answer this question, the Mary Robinson Foundation Climate Justice program issued its "Zero Carbon, Zero Poverty the Climate Justice Way" report this week. The study argues that keeping the world within the proper "carbon budget…can be achieved through a rapid peaking of the world's carbon emissions, by 2020, and a complete phase out of carbon emissions by 2050."

The carbon budget can be thought of as the amount of carbon dioxide the world can emit while still having a good chance of keeping the modeled average global temperature increase to less than 2°C above pre-industrial levels. In 2013, the Intergovernmental Panel on Climate Change calculated that staying within those limits requires humanity to not emit more than 1 trillion tons of carbon. (To get carbon dioxide equivalents, multiply by 3.67—that is, 11 tons of carbon dioxide equals about 3 tons of carbon.) As the World Resources Institute reports, humanity has already used up 515 billion tons of its carbon budget, which means that there's only 485 billion tons left. At current emissions rates, the remaining budget will be used up by 2045.

So how should the global carbon budget be allocated? Some draft provisions in the universal climate treaty aim to outline a fair way to divvy up the world's carbon budget. One proposed provision of the treaty notes that "the largest share of historical global emissions of greenhouse gases has originated in developed countries." Another provision directs greenhouse gas emissions reductions to take place "in accordance with historical responsibilities of developed countries and different socio-economic contexts and development stages of developed and developing country Parties." In other words, rich countries would be required to cut their emissions first and fastest because they have already used up more than their fair share of the world's carbon budget.

Before the U.N. climate change conference convenes in Paris, each country is supposed to submit its Intended Nationally Determined Contributions toward solving the climate problem. For example, the Obama administration has committed the U.S. to reducing its greenhouse gas emissions by 26-28 percent below their 2005 levels before 2025. Is this pledge and those made by other countries enough to keep the modeled global average temperature increase below 2°C?

No, says new report, "Fair Shares," issued earlier this week by a consortium of environmental activist organizations. The fair share activists' report delineates how they think the world's carbon budget should be allocated under the new treaty. In their calculations, they use carbon dioxide equivalent measurements so as to include the effects of other greenhouse gases, such as methane and nitrous oxide. If nothing is done to mitigate greenhouse emissions, the world will ostensibly be emitting the equivalent of 69 billion tons of carbon dioxide annually by 2030.

In order to stay on the modeled pathway toward keeping the world only 2°C warmer than the pre-industrial average temperature, the fair share activists assert, "Nothing less than a systemic transformation of our societies and our economies will suffice to solve the climate crisis." The systemic transformation would require that humanity cut our emissions 31 billion tons by 2030. The rich countries have so far pledged to reduce by 2030 their domestic greenhouse gas emissions by 5.5 billion tons and the poorer countries by 8.3 billion tons, leaving a gap of 17 billion tons between there and the activists' goal. Currently, the world emits the equivalent of about 50 billion tons of carbon dioxide annually, implying that global emissions will be 12 billion tons lower in 2030 than they are now.

What's the fair way to fill in the 17-billion-ton gap? The activists calculate that rich countries need to boost their domestic reductions from 5.5 billion tons to 9.1 billion tons. They also call for "a vast expansion of international finance, technology and capacity-building support." This means the rich countries should provide poor countries with the wherewithal to reduce by 15.1 billion tons the greenhouse gases they would otherwise have emitted. The amount that poor countries are expected to cut would actually be reduced from their current pledges of 8.3 billion tons to 6.6 billion tons. In other words, the activists reckon that it is only fair that poor countries greenhouse gas emissions be permitted to increase a bit as their economies develop.

What do the activists think is the U.S.'s fair share of reductions? Historically, the U.S. is responsible for about 30 percent of the cumulative emissions of carbon dioxide since 1850. The fair share activists calculate that the United States is promising to cut its annual emissions by only 2 billion tons by 2030. Without going into the arcana of the climate equity calculations, the activists argue that the U.S. should instead cut its emissions by the equivalent of 13 billion tons of carbon dioxide annually by 2030. According to the latest figures the U.S. emitted 6.7 billion tons of greenhouse gases in 2013. Under the most stringent interpretation of "historical responsibilities" for climate change, the U.S. would have to entirely eliminate all of its greenhouse emissions including those from electric power generation plants and automobiles by 2030. Meanwhile, Washington would be required to provide the money and technology to poor countries that would enable them to avoid annually emitting 7 billion tons of greenhouse gases in 2030.

This week, summing up where the climate negotiations in Bonn stand, one of the fair share activists—Harjeet Singh—bluntly said, "The money to prepare for and deal with climate impacts must be at the centre of the deal." No money, no agreement. In any case, it is a total fantasy to think that the U.S. and other rich countries will agree to a treaty that would require them to stop emitting greenhouse gases entirely in just 15 years.

Note: I will be reporting daily dispatches during the last week of climate treaty negotiations at the Paris conference in December.