With "99 per cent confidence", the 0.4 degree spike in temperatures over the preceding three decades could be ascribed to increased levels of greenhouse gas emissions, he said, adding the trend would have "implications other than for creature comforts".

"30 years later, it's clear [the model] simulations were skillful," Gavin Schmidt, who succeeded Hansen as head of NASA's Goddard Institute for Space Studies in 2014, tells Fairfax Media. "The predictions were quite good."

What was not so accurate was the expectation that politicians would listen to scientists, and act.

By 1990, the first Intergovernmental Panel on Climate Change report was demanding strong measures to curb carbon pollution. "I thought we'd see nations acting and a decline in total emissions," Pearman said.

Instead, we've had about 0.5 degrees further warming since 1988 as emissions have climbed, Rahmstorf said. Political leaders have attended dozens of United Nations conferences - where "they are deeply convinced we have to stop global warming very quickly" - only to drop the issue as a priority as soon as they return home.

"All their goals in life, as politicians, are under threat if we don't get global warming under control," he said.

Few weeks go by without peer-reviewed research detailing significant impacts of climate change or projections of the damage to come.

Heatwaves are among the clearest signals, with record-warm months now five times more likely than without the background warming, Rahmstorf says.

With half of the corals killed in the Great Barrier Reef's back-to-back bleaching over two summers, "it should be in the heart of every Australian to stop global warming," he said.

Up north, summer Arctic ice - important for reflecting solar radiation back to space - has lost three-quarters of its volume and half its area, Rahmstorf, an oceanographer, says.

Meanwhile, research out this month showing Antarctic ice sheets are melting at an increasing rate - pouring 200 billion tonnes of ice into the ocean annually - was "extremely concerning", NASA's Schmidt says.  The results "astonished me", he says. "It's clear things are changing very rapidly."

One effect of melting ice is that sea level rises are accelerating - although most of the increase so far is caused by thermal expansion as oceans absorb the bulk of extra heat being trapped by greenhouse gases.

Since the effect of gases already emitted take decades to play out, "it's likely we have 0.5 to 1 degree warming possibly, regardless of what we do with our emissions", Schmidt says.

Pearman's concerns include our lack of understanding on how our ecosystems will respond to rapid warming and other changes. South-western WA's rainfall has already dropped a third in recent decades, while eastern states' forests are becoming more bushfire prone, he says.

Rahmstorf worries extreme weather events are already causing "massive refugee movements" and the threat of governments "descending into chaos" are only going to increase.

Hansen himself has become increasingly frustrated most leaders have merely agreed "there's a problem". Promises like the Paris agreement to keep warming to well below 2 degrees "don’t mean much, it’s wishful thinking. It’s a hoax that governments have played on us since the 1990s”, he told The Guardian this week.

But causes for optimism remain, such as emissions starting to fall in Europe and the US - but not Australia. Prices of renewable energy also continue to slide, dislodging fossil fuels, the main emissions source.

"We can turn this around," Schmidt says. "It's not hopeless."

Or as Rahmstorf puts it less encouragingly: "It's never too late to prevent even worse disasters".