Australia’s bushfire crisis started much earlier than normal in August 2019, with thousands of fires in Queensland and New South Wales.

Despite the evidence a claim persists that a major contributing factor of Australia’s devastating fire season – and the deaths, loss of homes and environmental devastation they have caused – is not climate change but a conspiracy by environmentalists to “lock up” national parks and prevent hazard reduction activities such as prescribed burning and clearing of the forest floor.

On Saturday the prime minister, Scott Morrison, said after visiting fire grounds: “The most constant issue that has been raised with me has been the issue of managing fuel loads in national parks.”

He claimed that people “who say they are seeking those actions on climate change” could also be the same people who “don’t share the same urgency of dealing with hazard reduction”.

Prof David Bowman, the director of the fire centre research hub at the University of Tasmania, said: “It’s ridiculous. To frame this as an issue of hazard reduction in national parks is just lazy political rhetoric.”

On Sunday Morrison said he wanted to know “what the contribution of issues” around hazard reduction were, but repeated that it had been an issue raised often with him.

He also said “without the planning, without the preparations” of state agencies, “I fear what has really been a terrible tragedy would have been far worse.”

Are greenies stopping hazard reduction?

Hazard reduction is the management of fuel and can be carried out through prescribed burning, also known as controlled burning, and removing trees and vegetation, both dead and alive.

Hazard reduction is carried out by fire authorities, national park staff and individual property owners who can apply for permits to clear areas around their buildings. Coordination of activities happens through local bushfire management committees. There are 120 committees in NSW.

The claim of a conspiracy by environmentalists to block hazard reduction activities has been roundly rejected by bushfire experts, and experts say it is betrayed by hard data on actual hazard reduction activities in national parks.

Prof Ross Bradstock, the director of the centre for environmental risk management of bushfires at the University of Wollongong, has previously told Guardian Australia: “These are very tired and very old conspiracy theories that get a run after most major fires. They’ve been extensively dealt with in many inquiries.”

Former fire chiefs who have been calling strongly for action on climate change, and who have been trying to meet Morrison for months, have also been calling for increased funding for hazard reduction.

The Australian Greens say they want “an effective and sustainable strategy for fuel-reduction management that will protect biodiversity and moderate the effects of wildfire for the protection of people and assets, developed in consultation with experts, custodians and land managers”.

A federal government factsheet on bushfire management outlines how state agencies and people can carry out a range of hazard reduction activities that have been exempted from national environmental law, even if they “have the potential to have a significant impact on nationally protected matters”.

How much hazard reduction has happened?

In the last full fire season of 2018 and 2019, the National Parks and Wildlife Service in NSW told Guardian Australia it carried out hazard reduction activities across more than 139,000 hectares, slightly above its target.

There are two major restricting factors for carrying out prescribed burning. One is the availability of funds and personnel, and the second is the availability of weather windows.

The 2018-19 annual report of the NSW Rural Fire Service says: “The ability of the NSW RFS and partner agencies to complete hazard reduction activities is highly weather dependent, with limited windows of opportunity. Prolonged drought conditions in 2018-19 adversely affected the ability of agencies to complete hazard reduction works.”

The RFS said 113,130 properties had been subject to hazard reduction activities, which was 76% of its target. The 199,248ha covered was 106% of its target.

Is climate change affecting hazard reduction?

A former NSW fire and rescue commissioner, Greg Mullins, has written that the hotter and drier conditions, and the higher fire danger ratings, were preventing agencies from carrying out prescribed burning.

But as well as climate change narrowing the window to carry out prescribed burning, Mullins said some fires have become so intense they have burned through areas that had been subject to hazard reduction.

Mullins has been fighting fires in NSW for months. Speaking to the ABC on Friday, he said he witnessed a fire in Grafton in an area that had burned only two weeks previously, but “the burnt leaves were burning again”.

He said: “There has been lots of hazard reductions done over the years – more by national parks than previous years – but the fires have burned through those hazard reduction areas.”

Mullins dismissed suggestions that the bushfires were down to “greenies” preventing hazard reduction activities.“This is the blame game. We’ll blame arsonists, we’ll blame greenies,” he said.

“When will the penny drop with this government?”

The National Parks Association of NSW’s president, Anne Dickson, has also responded to the attacks on environmentalists.

In November 2019, she said: “The increasing intensity and frequency of fire is one of the greatest threats to biodiversity and natural landscapes. It may be politically expedient to pretend that conservationists exercise some mythical power over fire legislation and bushfire management committees, but it is not so.

“Such wild and simplistic claims avoid the very real and complex challenges of protecting our communities and the healthy environments that support our quality of life.”

Bowman said that separate to the “lazy political rhetoric” of blaming environmentalists, there should be an examination of the benefits and limitations of hazard reduction.

But he said there was also a reality to consider: “A lot of people are thinking that hazard reduction burning stops fire. It doesn’t, but what it does do is to try and change its behaviour.

“But let’s say you embarked on the biggest fire reduction program the world has ever seen. What’s the budget for that? Who will pay for it. Of course there is a place for hazard reduction but if you have massive increases, where does the money come from? The reality is that you can’t treat everything.”

What is climate change doing to bushfire weather?

The 2019-20 bushfire crisis coincided with Australia’s hottest year on record. On a state level, NSW easily experienced its hottest year, with temperatures 1.95C above the long-term average, beating the previous record year, 2018, by 0.27C.

Climate experts have said not all of that heat came from climate change, as two climate systems were also working to push up temperatures and fire danger.

Fire authorities are guided on a daily basis on the risk of fires through the Forest Fire Danger Index, a combined measure of temperature, humidity, wind speed and the availability of dry fuel. Spring 2019 had been the worst year on a record going back to 1950 for bushfire risk.

A 2017 study of 67 years of FFDI data found a “clear trend toward more dangerous conditions during spring and summer in southern Australia, including increased frequency and magnitude of extremes, as well as indicating an earlier start to the fire season”.

A study of Queensland’s historic 2018 bushfire season found the extreme temperatures that coincided with the fires were four time more likely because of human-caused climate.

On Sunday Morrison claimed the government had “always made this connection” between climate change and impacts on Australia’s weather.

Advice shared with authorities around the country earlier this year from the National Environmental Science Program said: “These trends are very likely to increase into the future, with climate models showing more dangerous weather conditions for bushfires throughout Australia due to increasing greenhouse gas emissions.”

There are also fears that large pulses of carbon dioxide emissions from Australia’s bushfires may not be reabsorbed through regrowth of forests as they have in the past.

The fire season has seen several reports of bushfire-generated thunderstorms. Guardian Australia has reported that 2019 would likely be a “stand-out” year for storms known as “pyroCBs” that generate their own lightning and influence the atmosphere at heights of up to 15km.

A study in 2019 published in the journal Scientific Reports found that adding more greenhouse gases to the atmosphere would create more dangerous conditions favourable to pyroCB events in the future, particularly for the southern parts of Australia.