"Christiana Figueres had a very unenviable position, and she's done an excellent job in holding the whole edifice together," Kevin Anderson, the deputy director of the Tyndall Center for Climate Change Research, told DW following the senior diplomat's decision last week not to seek a new term.
Figueres, a diplomat from Costa Rica who heads the Bonn-based UN secretariat for the Framework Convention on Climate, will leave her position in July after six years.
Anderson, who is also a professor of energy and climate change at the University of Manchester, believes Figueres and world leaders decided it was necessary to "water down" the agreement - stopping short of what is really required to avoid dangerous consequences for the planet.
"During her and her predecessors' watch, carbon dioxide emissions have not come down," he said. "In 2016, emissions will be 60 percent higher than in 1990." Anderson added that reaching the goals agreed to in Paris will be nowhere near enough to reduce the Earth's warming.
'Much too vague'
To reach the deal agreed to in Paris in December, Figueres brought together rich nations and poor ones, the states that pollute the most and those that pollute the least, and the countries that would benefit the most from a deal to ditch fossil fuels with those that stake their economies to them.
One hundred ninety-five countries committed to cutting carbon emissions in the agreement, which aims to keep the global average temperature increase below 2 degrees Celsius (3.6 Fahrenheit) - and ideally below 1.5 degree.
"Christina Figueres' greatest achievement was, no doubt, in getting all countries behind an agreement that admits 'climate change is happening, it's man-made, and we need to try everything to stop it,'" Ann Kathrin Schneider, a campaigner on international climate policy at Friends of the Earth Germany, told DW.
Schneider said, however, that the landmark agreement has "key weaknesses" and is "much too vague." She believes that another diplomat might have forced through more concrete action while delivering genuine "justice" for those nations most affected by climate change.
Original deal failed
Figueres was appointed to the role in May 2010, a low point for the UN's climate team after a summit in Copenhagen collapsed following a fallout between the leaders of wealthy and poor nations.
Previously, Figueres had worked as a climate negotiator in Costa Rica, where she was commended for her knowledge of how policy works at the local, national, and international levels. She also took part in discussions that led to the Kyoto Protocol, an international treaty that preceded COP21.
Neither Anderson nor Schneider thought that Figueres had been pressured not to seek another term.
"Because the agreement is so weak in terms of what it demands from each country, I couldn't name one government that maybe got so upset with the text that they have put pressure on her to step down," Schneider said.
Anderson said Figueres had been a "safe pair of hands," choosing to continue to "push the existing political-economic paradigm as hard as it can be pushed, even though it is no longer compatible with the goals that have been set out."
Almost a year before the deal to reduce CO2 emissions was struck in Paris, Figueres insisted that she was under no illusion as to the far-reaching consequences that countries would face over the next decades as they sought to bring down carbon emissions.
"This is the first time in the history of mankind that we are setting ourselves the task of intentionally transforming the economic development model that has been reigning since the industrial revolution," she told reporters in Brussels last February.
But Anderson said the deal that Figueres had pushed for would likely deliver a 3-4-degree average rise - twice the maximum agreed to in Paris.
"She thinks you can deliver more by pushing harder within the existing system than by questioning the system itself," said Anderson, who has written extensively in support of much stronger measures to tackle global warming.
"They're really just keeping their fingers crossed that highly speculative technology in the future will be able to suck large quantities of carbon dioxide out of the atmosphere," Anderson said. "They're using that to avoid asking difficult political questions today."
Schneider has called for Figueres' successor, who is likely to be named soon by UN Secretary General Ban Ki-moon, to cooperate more with civil society groups to pressure national governments into firmer commitments. Friends of the Earth has called for grassroots activism to call attention to some of the weaknesses of the deal released in Paris.
Anderson doesn't believe that the next UN climate chief will "significantly rock the boat."
"It's very unlikely that her replacement will really grapple with the scale of the increasing void between the rhetoric we hear on climate change and the scale of action that we now need," he said.