There’s a cafe next door to the thronging media centre at the UN global climate talks in Paris where the constant clang of the door to the chill air outside can barely be heard above the buzz.

Veteran climate scientist and biologist Prof Lesley Hughes has taken a seat with me close by and is struggling to hear herself think.

But the chaos and noise of the global climate talks are not enough to drown out her feeling that a historic moment could be only hours away.

Minutes earlier, scientists delivered a dose of sobering reality to negotiators from a meeting room where journalists took up every seat and then every square metre of floor space.

“We still have 24 hours to pull something stronger together,” said Kevin Anderson, deputy director of the Tyndall Centre for Climate Change Research in Manchester, England.

What was currently in the draft text of the new Paris deal was, according to Anderson, “somewhere between dangerous and deadly” for the most vulnerable nations in the world. Others would disagree.

All the scientists here do agree that a new global deal, now expected to be put up for agreement sometime on Saturday, needed to match the scientific realities of keeping global warming to well below 2C while aiming for 1.5C.

For that, the conclusions were simple. By the back end of the century, or perhaps much earlier, global greenhouse gas emissions needed to hit zero.

The deal, said the scientists, was a long way from perfect, but most seemed optimistic that it was a strong basis for improvement.

Australia’s Hughes, from Macquarie University, has been in climate research since 1990.

As famous climate campaigner Bill McKibben hurries through the clanging glass door, she is choosing an optimistic tone. “Unless you are hopeful, then you may as well give up,” she says. “The only hope for the planet is to stay hopeful.”

In 1994, Hughes was a co-author on a controversial paper in Nature that for the first time estimated how many species were at risk from extinction from climate change. As many as a third of all species could die out from climate change, the paper found.

She authored an influential paper in 2000 in the journal Trends in Ecology and Evolution that for the first time brought together data from around the world to find that plants and animals were already showing impacts from increased levels of greenhouse gases in the atmosphere.

Hughes says that back in 1990 when she began researching climate change impacts on ecosystems, terms like carbon footprint had not even been invented.

“Back then climate change felt like a long way off. It was an academic thing. I could never have envisaged being at an international meeting with 40,000 delegates from 190 countries to agree a global agreement. It was beyond imagining.”

Fellow Australian professor Ove Hoegh-Guldberg, of the University of Queensland, has been in Paris for two weeks. He’s in his Airbnb accommodation close to St Michel taking an hour or two’s break from the Le Bourget venue across town.

The marine biologist has been researching the impacts of global warming and greenhouse gases on coral reefs since the mid 1980s. He first dived on the Great Barrier Reef in 1969 with his grandfather.

“I started this in 1984 at the start of my thesis. I was looking into why it was that corals were going white in some parts of the world.”

Hoegh-Guldberg’s work, beginning with a scientific paper in 1989, found that what might seem like modest rises in sea temperatures could have terminal consequences for coral reefs across the world.

“By the end of the next decade I combined projected sea temperature rises with the known tolerances of corals and I realised we would lose a lot [of corals] by mid-century with a doubling of CO2.”

Hoegh-Guldberg says he is “shocked” at even the prospect of a deal being struck this weekend in Paris.

“I thought that we might have had a Copenhagen moment – but people seem to be coming from a position of working with the system, instead of gaming it.”

What delights Hoegh-Guldberg even more is that under the current draft of the Paris agreement, there’s a statement that calls for countries to keep global warming “well below 2C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5C”.

That statement, he says, matches almost word for word a call that Hoegh-Guldberg and other world leading coral scientists made in the lead up to the Paris talks.

“I thought that request was a little extreme,” he admits.

“But now it’s there in the text. But I am very conscious that the real work comes now. The [pledges] from countries get us to about 3C of warming. That’s disastrous for coral reefs.”

Making sure the Paris agreement forced countries to regularly review their pledges so that “well below 2C” becomes a reality is something all scientists here in Paris seem to agree with.

But Hoegh-Guldberg, and no doubt the other scientists here, declares an interest.

“The Great Barrier Reef is a place that I’m grafted to,” he says. “The best place for me isn’t a wine bar but on a reef, diving. So I’m declaring the planet as my vested interest.”