The hot and dry conditions that helped drive Australia’s bushfire crisis would be eight times more likely to happen if global heating reached 2C, according to new analysis.

An international team of scientists also found the risk of Australia being hit by intense fire weather had already risen since 1900 “by more than a factor of four”.

And the scientists said it was “scary” a country as well prepared for tackling bushfires as Australia had seen its systems “severely strained” by what the called the Black Summer Bushfires.

Australia’s bushfire crisis began in spring 2019 and burned at least 7.7m hectares in the south of the country, claiming 34 lives and causing an environmental disaster. More than a billion animals were killed and threatened species were pushed towards extinction. Thousands of homes were destroyed.

The 17 scientists from across Europe and the US, used computer climate models to examine the impact of increased levels of greenhouse gases in the atmosphere on the risk of intense fires.

The bushfire study used the computer models to look at a metric called the Fire Weather Index, which is one way to predict the severity of fires by combining wind speed, relative humidity, temperature, drought and the flammability of the fuel. The index is widely used across the world to forecast dangerous wildfire conditions.

The models found the probability of the index reaching levels seen during Australia’s bushfires had increased due to human-caused climate change by 30%.

But the scientists said the influence of extra greenhouse gases was likely much higher because when they compared the climate models to the actual temperatures, they found the models underestimated the extreme heat seen during the bushfires.

Prof Geert Jan van Oldenborgh, lead author of the study, of the Royal Netherlands Meteorological Institute, said: “We found that climate models struggle to reproduce these extreme events and their trends realistically.

“However, they always underestimate the increase in chances for extreme fire risks such as Australia saw in the last few months. This means we know the effect is likely larger than 30% increase lower bound, which is already a significant influence of global warming.”

The analysis also looked at conditions under a climate that warms by 2C above the pre-industrial levels. Two climate models found that fire weather conditions like those seen in 2019 “become about eight times more likely” in a 2C world, with a “lower bound of four times more likely.”

The study released on Thursday has not been peer reviewed, but is being submitted to a journal with all data being made available. The methods and climate models had been used in previous studies that had been peer reviewed, they said.

Dr Sophie Lewis, a co-author of the study from the University of New South Wales, told a briefing the fires had broken out during Australia’s hottest and driest year on record.

She said new records had been set for high Forest Fire Danger Index in all states and territories throughout the 2019 spring.

Lewis, who is based in Canberra, recalled being stuck in her own home with a young family for weeks to avoid the heavy smoke from the bushfires.

She said: “In January, the national park that forms a large part of our home in Canberra exploded in flames. It was just last week the fire was declared out.

“Clearly this was an event with an enormous ecological and human cost. It’s because of this that it’s so important to understand the contributing factors to this.”

Looking only at observations, the scientists found the chances of Australia experiencing Fire Weather Index ratings as high as 2019 had already risen by “more than a factor of four” since 1900.

The scientists that analysed the bushfire conditions are part of a project called World Weather Attribution that has examined the human influence on previous extreme events, including the 2016 bleaching of the Great Barrier Reef.

That analysis found human-caused climate change had made the heat during the bleaching event 175 times more likely to happen.

Co-author Maarten van Aalst, director of the Red Cross Red Crescent Climate Centre in the Netherlands, said it was “really scary that we are seeing such extreme conditions in countries that are as well prepared [for bushfires] as Australia.”

He said: “What’s really obvious in light of these findings of rising risk is that it will become even more important to build resilience and prepare for these rising risks.

“But there are also limits to what we can do through that adaptation and preparedness. So it’s critical that we find ways of reducing the underlying drivers of these rising risks to avoid problems getting even further out of hand in the future.”

Dr Sarah Perkins-Kirkpatrick, a UNSW climate scientist who examines extreme events who was not an author on the study, said: “Fire weather is a very complex thing to simulate.

“Combined with everything about this event being unprecedented, its extremely challenging for climate models to simulate everything about fire weather perfectly.

“Australia just just experienced its worst bushfire season on record, overlapping our warmest and driest year on record. We know climate change has a role in increasing temperatures, which is a component in bushfire weather.”