This week, New Zealand woman Bonnie Callagher likened the 25m-high flames approaching her New South Wales home to "looking into the gates of Hades".

According to a Kiwi scientist who studies extreme fire behaviour, it was probably an accurate summation.

"If you were standing in front of your house watching the fire coming at you, it would be quite a terrifying experience – you'd be feeling the extreme heat, even when being hundreds of metres away," Scion's Grant Pearce told the Herald.

'Like night'

If we could somehow put ourselves amid those monster fires tearing through New South Wales' lofty eucalypt forests, it might well be like standing in the thick of Hell.

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Daytime darkness, ember storms, howling, sucking wind, unbearable heat and an immense, fast-moving wall of fire.

Consider the figures: towering flames burning at up to 1300C, and reaching right to the canopies of trees, 20m to 30m, potentially even 50m, above the ground.

Pearce had even heard reports of grass fires at the flame front climbing six to eight metres high – and burning deep.

"You might think of a normal grass fire being only two metres wide as it runs … these fires are likely running hundreds of metres deep, all because of the residual fuel on the ground that burns for much longer."

While the surrounding air temperature stretched over 40C, winds had been gusting, in some areas, at 65km/h.

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When the inferno essentially became a firestorm, conditions became dark – "almost like night time" – and the air filled with masses of burning firebrands.

"You've got twigs, and pieces of bark and leaves, thousands of them, all glowing and being whipped up by the wind at flying at you like in a sandstorm," he said.

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"When these fires come through the forest, they also generate a lot of noise: they're described as sounding like a freight train running down a track.

An out-of-control bushfire threatens Johns River in New South Wales. Photo / Nathan Edwards
An out-of-control bushfire threatens Johns River in New South Wales. Photo / Nathan Edwards

"There's a real rumble to them, along with the crackling and popping of things burning, so there's a massive noise going on."

Another dramatic feature of these bushfires were their gigantic plumes of smoke, clearly visible from space and big enough to create their own weather.

"With such massive areas burning, these fires create so much heat that it gets lifted into the air, creating a smoke-filled convection column," he said.

"As that heated air rises in the smoke column, it draws in air from the ground, which fans the fire even further.

"All of these smoke columns can rise several kilometres into the atmosphere, making big nuclear bomb-like clouds that can generate thunderstorms."

The sheer pace of the fires – spreading at distances of up to 12km each hour – was similarly frightening, and another reason why attacking them from the front was nearly impossible.

"Because these fires are generating so much heat, you can't get close enough to use pumps, hoses and fire trucks anyway – with that sort of on-the-ground activity, you're wasting your time."

Fighting the beast

As at this morning, more than 80 fires – of which half were out of control, with a dozen having reached "emergency level" were burning across New South Wales alone.

Both New South Wales and Queensland have now both declared states of emergencies, three people have died, and more than 170 homes have been destroyed.

In big infernos, crews instead approached them from the flanks, and the rear, where they were moving the slowest.

Large helicopters and "water-bomber" fixed-wing aircraft were being used to drop retardant on the fires – but even around the edges, the fires were burning so hot that any water dispersed evaporated before it hit the ground.

Crews had been using all of the traditional strategies of rural firefighting: creating control lines around the fire with heavy machinery, and protecting homes and infrastructure by dropping retardant on them.

In some cases, it was possible to "backburn" from fire breaks and control lines, to remove any fuel that would feed them.

"This practice is more common in Australia, but only rarely used here in New Zealand."

Unsurprisingly, the work of fighting the fire was incredibly testing.

"These volunteers come from all walks of life – that's everyone from athletes through to the older people who don't get quite as much exercise – and they're constantly doing activity like dragging fully charged water hoses, and using hand tools to cut lines," Pearce said.

"Work by my colleagues has shown that when these firefighters are doing these arduous tasks, it's equivalent to what elite athletes experience, with heart rates exceeding 150 beats per minute.

"On top of that, they're getting smoke exposure, which can mean breathing difficulties."

He pointed out that rural firefighters didn't wear the same equipment – fireproof coats, heavy woollen clothing and breathing apparatus – that their urban counterparts used in structure fires.

"That's because they'd quickly overheat just from the heart that the body builds up: so they use much lighter overalls that are treated with fireproof materials and chemicals," he said.

"This provides a little bit of protection, but also allows the heat generated by the body to escape through the neck, collar and sleeves.

"They'll have helmets, and might have a standard mask, if they are working around those dusty, dry conditions.

"But they're not going to have any other protective clothing. It's about not putting yourself in dangerous positions."

Pearce said their shifts would be long – sometimes stretching to 12 to 14 hours each day, over several days, in each rotation.

"The management team co-ordinators try to manage that, but it's really difficult when you get a new fire outbreak to deal with," he said.

"Generally, they're working in really hard, short bursts, they get a bit of spell, move on to somewhere else, then get back into it."

New Zealand crews now operating in North Queensland are working up to 14 hour shifts for two five-day rotations, with a rest day between the rotations and a travel day on either side.

Climate change in action?

The unprecedented scale of the Australian fires has led many to question whether this was climate change in action.

Dozens of fires are still burning out of control across eastern Australia. Photo / QFES
Dozens of fires are still burning out of control across eastern Australia. Photo / QFES

Scientists suggest a warming world has indeed played a part, influencing climate drivers that primed eastern Australia to burn.

"To understand the role of climate change in these fires we first need to see where each and every Australian climate driver is sitting at the present moment," explained Dr Paul Read, co-director of Australia's National Centre for Research in Bushfire and Arson.

"An anomaly outside of their combined effects - and there have already been several temperatures much higher than seasonally expected - could suggest climate change, especially if the evidence for other anomalies emerge from, for example, farmers' and firefighters' datasets alongside bureau meteorological trends."

The continent was coming out of a negative Southern Annular Mode, which had caused drought from hotter westerly winds.

"The fuel load is already crisp, and we've been getting deeper into the hot cycle of the El Nino Southern Oscillation since late 2018."

On a much longer timeframe, Read added, the world was supposed to be entering a cold-snap, based on how the Earth's climate had behaved over thousands of years – "but temperatures around the world have been knocking over records for hottest years and even decades".

"So is it climate change? The jury's always out when it comes to science, as it should be, but I'd lay bets that it is climate change affecting our seasons. And this is scary for everybody.

Rural firefighters in eastern Australia have often been working at rates comparable to elite athletes. Photo / QFES
Rural firefighters in eastern Australia have often been working at rates comparable to elite athletes. Photo / QFES

"We need to sensibly, gently, but rapidly, adjust our ways of doing economics and politics worldwide, at the same time strengthening our capacity to cope with natural and man-made disasters. Bushfires are, after all, a combination of both."

The rise of 'extreme fire'

For New Zealand, climate change lifted the threat of wildfires behaving the way they are now across the Tasman.

While rural fires cause about $100 million in damage in this country each year, what's called extreme fire presents an entirely new threat.

That's because their unpredictable and dynamic conditions could put firefighters at greater risk, particularly if the fire spreads behind them.

Conditions that increase extreme fire risk include mid to high temperatures, low humidity and wind speeds gusting at 50km/h to 70km/h.

These include spotting, where embers and other particles are hurled ahead of the fire front, fire tornadoes and whirls, and "blow-up" conditions, where the inferno suddenly escalates in size and intensity.

The few cases of extreme fire that New Zealand has seen over recent years have all been dramatic.

Source / Scion
Source / Scion

They included a fire that scorched 90ha of land near Hanmer Springs in 2016, the devastating Port Hills fire near Christchurch in 2017, and the big blaze that tore across 35km of Nelson's Pigeon Valley in February.

Under climate-change scenarios projected to deliver several degrees of average temperature increase and stronger and more frequent westerly winds, the number of extreme fires will double or treble by the end of the century - perhaps even by 2050.

Population growth, more people moving to rural areas, and a changing landscape bringing different fuel sources, such as wilding pines, would push the danger yet higher.