Delegates attend the opening of the Intergovernmental Panel on Climate Change (IPCC) at the Tivoli Congress Center in Copenhagen on October 27, 2014. (AFP PHOTO/Getty Images)

On Sunday, the United Nations' Intergovernmental Panel on Climate Change, the world's leading authority on the science of global warming, released its latest "Synthesis Report." And it painted a pretty dire picture.

Significant global warming, the report said, is already "irreversible" -- and if policymakers don't act, a dangerous 2 degrees Celsius (3.6 degrees Fahrenheit) warming threshold will be breached.

That's a strong message -- but it might have been even stronger. You see, one of the report's more powerful sections wound up being left out during last minute negotiations over the text in Copenhagen. And it was a section that, among other matters, tried to specify other measures that would indicate whether we are entering a danger zone of profound climate impact, and just how dramatic emissions cuts will have to be in order to avoid crossing that threshold.

This outcome -- and the divergent national views underlying it -- is a prelude to the political tensions we can expect at next month's mega climate change meeting in Lima, Peru, and then especially in Paris at the end of 2015, when governments will gather to try to negotiate a global agreement to reduce greenhouse gas emissions.

The dropped section in question appeared in an August 25, 2014 draft of the synthesis report, but not in the final version. It was a box entitled "Information Relevant to Article 2 of the UNFCCC" or United Nations Framework Convention on Climate Change, a global treaty signed in 1992-93 by over 160 nations of the world, including the United States. The box would have comprised two pages in the final report, and was worked on by a team of scientists for nearly three years, according to Jean-Pascal van Ypersele, a Belgian climate researcher who is vice-chair of the IPCC.

Right after the report was approved, van Ypersele tweeted about the box's exclusion:

To understand why this box was so controversial, you first have to understand the significance of the UNFCCC -- which the US signed on to way back in the George H.W. Bush administration, long before views on environmental issues were as politically polarized as they are now. This treaty contains a famous section, Article 2, which states that the signatory nations aim to prevent "dangerous anthropogenic interference with the climate system." To this end, it says, greenhouse gas levels in the atmosphere should be stabilized "within a time-frame sufficient" to stave off all the more severe outcomes.

So in trying to explain how their research is relevant to this treaty, the scientists were necessarily walking a fine line between two realms -- that of politics and that of cold hard fact. Thus, the box they created listed climate change impacts of a magnitude that would constitute "reasons for concern," because they might imperil unique ecosystems or risk catastrophic one-off events like the collapse of global ice sheets.

It also discussed what it would take to stabilize climate change in “sufficient” time  to stave off these worst impacts. On this subject, the box stated that "rapid and deep emission reductions" would be required to keep global warming below 2 degrees Celsius. Indeed, it stated, the world can only emit about 1000 more gigatonnes of carbon dioxide (one gigatonne is equivalent to a billion tonnes) in the remainder of this century, adding that "at current rates, this remaining budget will be exhausted in the next 20 to 30 years."

Asked about the reasons for the box's omission, IPCC spokesman Jonathan Lynn said that "the entire report" remains relevant to Article II of the UNFCCC. The box, he says, "was an attempt to compile the most relevant information from the report into one place. At the meeting, many delegates felt that the proposed language or alternative proposals for the wording of the box were unbalanced. In discussions among delegates and scientists it eventually proved impossible to find language that everyone could accept. The meeting concluded that a separate box was unnecessary given the wealth of relevant information throughout the report."

But some scientists involved in the process -- while affirming that the final report remains an excellent document -- lament that an accommodation could not be reached. The box "provided a very precise [time] frame for the emissions that are compatible with a 2 degree of warming," says van Ypersele, who was part of the core writing team for the report.  "And there is no similar sentence anywhere in the report."

Michael Oppenheimer, a climate scientist at Princeton who was also part of the core writing team, suggests that politics got in the way of the inclusion of this scientific information. The science relating to what Article II of the UNFCC requires countries to do, he admits, falls "into that sensitive area. But in my view," Oppenheimer continues, "the governments should back off from their worries about the framework convention when they’re negotiating over IPCC text. Otherwise they're not going to be getting good analysis."

The way the IPCC works is that the scientific texts are written by scientists, but they also have to be approved by governments. Thus scientists can veto inaccuracies, but governments can also prevent the inclusion of certain content. Oppenheimer says the IPCC process is unique in this way, and thinks that the box could have been modified to suit all the parties involved if there had been more time for negotiations. But "in the end, the governments couldn’t reach an agreement," says Oppenheimer, "and time ran out, and the box fell by the wayside."

So where did the political tension come from? One critical schism, when it comes to the UNFCCC, involves the relationship between developed countries -- those who have emitted voluminous greenhouse gases over the years to achieve economic prosperity -- and developing countries, who might suffer from climate change impacts that they had little or no role in causing. Indeed, concerns about inequality are hard to avoid in talking about the UNFCCC; thus, the box explicitly stated that "risks of impacts pose particular challenges for the least developed countries and most vulnerable communities."

Another reason this topic is "extremely sensitive," says van Ypersele, is that not everybody agrees that 2 degrees Celsius is even a safe threshold at all. Many think 1.5 degrees would be safer -- a number that would imply a much tighter global carbon budget and an even narrower window to avoid "dangerous" climate change.

The Copenhagen Accord, adopted at the 2009 Copenhagen conference of parties to the UNFCCC, explicitly sets 2 degrees Celsius as the threshold number beyond which we would cross over into a danger zone. But it also calls for an " be completed by 2015" that would "include consideration" of whether the number should actually be changed to 1.5 degrees. That debate, van Ypersele suggests, may have spilled over into the IPCC process.

So for all of these reasons, making scientific statements that were of such close relevance to the UNFCCC may have been a bridge too far -- especially in the time allotted. And the IPCC is, in the end, a hybrid process that is both scientific but also political.

"I have a very strong view that scientists have a last word on what is in the report," says van Ypersele. "What they don’t have the last word on is what is not in the report."