Students striking over climate change inaction have been described as victims of "politically correct teaching" and include some who are "barely literate or numerate".

Thousands of young people across the country — and countless more worldwide — will walk out of school on Friday in a global day of action to incite governments to do more to reduce fossil fuel emissions.

Organisers believe crowd numbers will be triple those of student strikes held in November.

But Dr Kevin Donnelly, a conservative commentator and senior research fellow at the Australian Catholic University, claimed the movement was the product of "biased" academics and failings in education.

"I've just been on the Strike 4 Climate webpage, where you've got seven or eight-year-old kids barely out of nappies being involved in a strike," he told ABC Radio Adelaide.

"A lot of these students are barely literate or numerate.

"I think it's absurd."

Organisers are expecting bigger crowds than those in November. ( ABC Radio Adelaide: Malcolm Sutton )

Dr Donnelly, an education expert who has written about political correctness which he says is "destroying" Australia, said 1,000 international scientists had dissenting views about the cause and extent of climate change.

He said there had been next to no recognition of this by academics who support the striking students.

"It's all very well to be politically correct, but there's no rationality or reason behind it that stands up," he said, adding that students should protest on the weekend so they didn't miss school.

"We're going backwards in international testing in terms of maths, science and English, and I really suggest they should be putting the effort into raising standards rather than stunts like this."

'We'll be striking every Friday'

Nyah Bacon has threatened to strike every Friday over climate change inaction. ( ABC Radio Adelaide: Malcolm Sutton )

Adelaide Year 10 student Nyah Bacon said the School Strike 4 Climate movement had three goals: to stop Queensland's Adani coal mine, to ban new fossil fuel exploration, and to have Australia commit to 100 per cent renewable energy by 2030.

She will be among the 3,000 young people expected to gather outside the SA Parliament for an 11:00am protest on Friday.

"We never expected anything this global or this large and it's amazing to see how far it has come," Nyah said.

"And to continue this movement, we'll be striking every Friday on the Parliament steps until our demands are met."

Nyah recently returned from Sweden where she participated in Friday strikes with Greta Thunberg, the teenager who inspired the global movement.

Greta has regularly protested outside the parliament in Stockholm since August and vows to do so until Sweden makes good on its commitments under the Paris climate agreement.

Students in 98 countries have now taken similar action against their governments.

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'They have every right'

Professor Mark Howden, director of the Australian National University's Climate Change Institute, said young people had every right to be concerned about climate change and "the world in which they're going to live".

He said he could understand why people might get upset about the short-term impacts of shutting down coal-fired power stations and transitioning to renewable energy.

"But I would suggest that school children have a different timeframe in mind," Professor Howden said.

"They're obviously concerned about the next 10 years, but they're also concerned about the next 50, and that's where I think the motivation for these climate strikes is coming from.

"These young people in their teens, they're going to be around when the Earth could be as much as three or four degrees warmer, and that would be an extremely challenging proposition for them."

Global warming recorded

The United Nations in February announced that 20 of the past 22 years had been the hottest on record.

Drawing from US, British, Japanese and European data, it said 2018 had been the fourth highest on record and cited a litany of extreme weather events across the globe such as wildfires, droughts and floods.

"The long-term temperature trends are far more important than the ranking of individual years, and that trend is an upward one," the UN's World Meteorological Organisation secretary-general Petteri Taalas said.

Australia endured its hottest summer on record during 2018-19, according to the Climate Council, when more than 200 extreme weather records were broken across the country.