The federal emissions reduction minister has defended Australia's land management practices after a new United Nations climate change report called for changes in the way the world produces and consumes food.

The UN's Intergovernmental Panel on Climate Change warned efforts to limit global warming while feeding a booming population could be wrecked without swift and sweeping changes to how we use the land we live off.

The report on land use and climate change highlighted the need to protect remaining tropical forests as a bulkhead against future warming.

It offered a sobering take on the hope that reforestation and bio-fuel schemes alone can offset mankind's environmental damage, underlining that reducing emissions will be central to averting disaster.

"Land is a source of emissions as well as a sink," IPCC chair Hoesung Lee told AFP.

"Obviously you want to reduce emissions from land as much as possible. But that has a lot to do with what's happening to the other side of the equation: greenhouse gas emissions, mainly from the energy sector."

But Emissions Reduction Minister Angus Taylor said Australia is already absorbing emissions from land management.

"This is a very, very important success story in Australia. Farmers, in particular, haven't been given the credit they deserve for the role, the enormous role, they've played on this front," he told ABC News on Friday.

But the minister brushed off concerns about the role meat-heavy diets play in climate change, suggesting the report was "forcing" people to become vegan.

"We're not going to tell people what they should be eating, that's just not the role of government," he said.

Land is intimately linked to climate. With its forests, plants, and soil it sucks up and stores around one-third of all man-made emissions.

The climate crisis is increasing the intensity & frequency of extreme weather events, forcing people to flee their homes. Find out more about disaster displacement from @refugees: https://t.co/AGEtYcMsRqpic.twitter.com/qHJhMb0247 — United Nations (@UN) August 8, 2019

Intensive exploitation of these resources also produces huge amounts of planet-warming CO2, methane and nitrous oxide, while agriculture guzzles up 70 percent of Earth's freshwater supply.

National Farmers Federation president Fiona Simson said the food warning should send "a shiver down your spine".

The Australian red meat industry has a target to be carbon neutral by 2030, she added, noting the local agriculture industry produced ust a fraction of the world's food and fibre.

But Ms Simson was surprised the report flagged reducing food waste as a means to reduce climate change.

"There are tonnes and tonnes of food that is wasted at the point of production," she told ABC News.

"Sometimes it's about misshapen vegies, carrots that look weird or those sorts of things, but also sometimes we just haven't got the labour to pick the produce in the fields.

As the global population balloons towards 10 billion by mid-century, how land is managed by governments, industry and farmers will play a key role in limiting or accelerating the worst excesses of climate change.

Farmers for Climate Action want the federal government to implement a national strategy on climate change and agriculture, and to speed up the transition to clean energy.

"With NSW marking one year since it was 100 per cent drought-declared ... and farmers across the country hurting from droughts, heatwaves and other extreme weather events, it is clear that climate change is already hurting Australian agriculture," the group said in a statement.

"Farmers are adopting climate-smart agricultural practices, including soil carbon sequestration. But agriculture cannot be left to carry the burden on this alone."

Teenage climate campaigner Greta Thunberg, who along with a group of activists presented IPCC co-chairs with a thank you letter in Geneva, said she hoped governments would act on the report's findings.

"Of course if you are a very powerful person in a very powerful position then I think you should definitely read it," the 16-year-old said.

"I just hope that the conclusion of this report becomes in a way common knowledge, so everyone knows the importance of those numbers and facts within a bigger perspective."

Trade-offs

The IPCC is the world's leading authority on climate change. Last year it warned that limiting global warming to 1.5 degrees - the optimal level aimed for in the Paris climate deal - would be impossible without a drastic draw down in greenhouse gas emissions.

Its land-use report presented a string of looming trade-offs in using land for climate change mitigation.

Forests, an enormous carbon sink, can be regenerated to cool the planet. But with industrial farming covering a third of land today, there's limited space.

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Bioenergy in the form of vegetation used to sequester carbon also has potential. But room for that must be carved from cropland, pastures or existing forests.

The report said that a "limited" allocation of land for bioenergy schemes could indeed benefit the climate.

It warned however that deployment at a scale needed to draw down billions of tonnes of CO2 from the atmosphere each year "could increase risks for desertification, land degradation, food security, and sustainable development."

Devastating impacts

The 1,000-page report takes a deep dive into the systems we use to feed ourselves and the devastating impacts they are wreaking.

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Not only does agriculture and its supply lines account for as much as 37 percent of all man-made emissions, but current industrialised production and global food chains also contribute to vast food inequality.

The report noted that while there are currently two billion overweight or obese adults, 820 million people still don't get enough calories.

In addition, a third of all food produced is currently either lost or wasted, adding to mankind's carbon footprint.

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The IPCC summary paper mostly steered clear of the controversial call to limit meat consumption but did burnish the credentials of "plant-based foods" and their ability to mitigate global emissions.

"There's a wide range of food systems that rely on meat, and many people rely on meat for protein," Cynthia Rosenzweig, a NASA climatologist, and report author told AFP.

"But we do need to develop low greenhouse gas meat-producing systems."

Temperature matters

The report considers a quintet of human development projections, from a low-consumption global society that feeds itself sustainably, to a resource-intense future where arable land is squeezed out by huge-scale bioenergy projects.

But under all scenarios, one axiom held true: the higher the temperature, the higher the risk.

"New knowledge shows an increase in risks from dryland water scarcity, fire damage, permafrost degradation, and food system instability, even for global warming of around 1.5C," said Valerie Masson-Delmotte, an IPCC co-chair.

At 2C the risk of food insecurity ticks over to "very high".

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"It's not only about reducing emissions," said Ms Thunberg.

"The science says that to stay below 1.5C of global temperature rise we need to make unprecedented changes in all aspects of society.

"Those are not my words. Those are their words."