The world must turn towards healthy plant-based diets to stop climate change, a UN-backed report has warned.

Our food system accounts for between 25 and 30 per cent of greenhouse gases, and is choking the life from fresh and coastal waterways with excess nitrogen.

In order to feed the predicted 9.8 billion people on Earth in 2050, the world will need to produce 56 per cent more food compared to 2010.

If the level of meat and dairy consumption rises in line with current food habits, six million square kilometres (2.3 million square miles) of forests would need to be converted to agriculture - an area twice the size of India.

Two-thirds would be changed to pasture land, with the final third being used for crops, according to the Creating a Sustainable Food Future report.

The world must turn towards healthy plant-based diets to stop climate change, a UN-backed report has warned (file photo)

HOW DOES EATING MEAT AND DAIRY PRODUCTS HURT THE ENVIRONMENT? Eating meat, eggs and dairy products hurts the environment in a number of different ways. Cows, pigs and other farm animals release huge amounts of methane into the atmosphere. While there is less methane in the atmosphere than other greenhouse gases, it is around 25 times more effective than carbon dioxide at trapping heat. Raising livestock also means converting forests into agricultural land, meaning CO2-absorbing trees are being cut down, further adding to climate change. More trees are cut down to convert land for crop growing, as around a third of all grain produced in the world is used to feed animals raised for human consumption. Factory farms and crop growing also requires massive amounts of water, with 542 litres of water being used to produce just a single chicken breast. As well as this, the nitrogen-based fertiliser used on crops adds to nitrous oxide emissions. Nitrous oxide is around 300 times more effective at trapping heat in the atmosphere. These fertilisers can also end up in rivers, further adding to pollution. Overall, studies have shown that going vegetarian can reduce your carbon emissions from food by half. Going vegan can reduce this further still. Advertisement

Johan Rockstrom, former director of the Potsdam Institute of Climate Change Impact Research, said: 'To have any chance of feeding ten billion people in 2050 within planetary boundaries, we must adopt a healthy, plant-based diet, cut food waste, and invest in technologies that reduce environmental impacts.'

The 'great food transformation' proposed in the report is at odds with other schemes that aim to tackle greenhouse gas emissions.

One report by the UN's Intergovernmental Panel on Climate Change (IPCC) proposes to convert areas the size of India to biofuel crops or CO2-absorbing trees.

Nearly all Paris-compatible climate models slot in a major role for a two-step process that draws down carbon by growing biofuels, and then captures CO2 released when the plants are burned to generate energy.

The amount of 'bioenergy with carbon capture and storage', or BECCS, required in coming decades will depend on how quickly we sideline fossil fuels and shrink our carbon footprints.

Capping global warming at 1.5C would require converting some 7.6 million square kilometres (2.9 million square miles) to BECCS.

Even if temperatures were allowed to climb twice as high, the report concluded, biofuels would still need to cover some 5 million square kilometres (1.9 million square miles).

But these proposals 'could compromise sustainable development with increased risks - and potentially irreversible consequences - for food security, desertification and land degradation,' a draft summary of the 1,000-page IPCC report warns.

Meanwhile, the fundamental drivers of Earth's environmental meltdown - CO2 and methane emissions, nitrogen and plastics pollution, human population - continue to expand at record rates, further reducing our margin for manoeuvre.

To have at least a 50/50 chance of capping global warming at 1.5C - the temperature guardrail laid down in a landmark IPCC report last year - civilisation must be 'carbon neutral' within three decades.

Earth's surface temperature has already risen 1C above pre-industrial levels, enough to trigger deadly extreme weather and sea level rise that could swamp coastal megacities by 2100.

Our food system accounts for between 25 and 30 per cent of greenhouse gases, and is choking the life from fresh and coastal waterways with nitrogen (file photo)

One report by the UN's Intergovernmental Panel on Climate Change (IPCC) proposes to convert areas the size of India to biofuel crops or CO2-absorbing trees. Pictured: the World Meteorological Organization ahead of the IPCC session

And yet, 2018 saw a record 41.5 billion tonnes of planet-warming CO2 added to the atmosphere, up two per cent from the previous record, set the year before.

At this pace, humanity will exhaust its 'carbon budget' for a 1.5C world before US congresswoman Alexandria Ocasio-Cortez, co-sponsor of the Green New Deal, turns 45 (in 16 years).

'Forest restoration is the best climate change solution available today,' said Tom Crowther, a professor at the university ETH Zurich.

'If we act now, this could cut carbon dioxide in the atmosphere by up to 25 per cent, to levels last seen almost a century ago.'

Crowther's 'trillion tree' initiative made headlines, but has come in for a drubbing.

His calculations, according to several climate scientists, appear to assume that every tonne of CO2 stored in replanted trees would be a tonne of CO2 removed from the atmosphere.

In fact, the ratio is 2:1 due to the nature of Earth's carbon cycle, which vastly reduces the scheme's projected benefits.

In addition, it takes decades for trees to reach their maximum CO2-absorbing potential, as the authors themselves point out.

Other critics warn against the 'moral hazard' of an apparently simple solution that may dampen resolve to purge fossil fuels from the global economy, a danger underscored, perhaps, by the enthusiasm of oil and gas giants for planting trees.

'Heroic reforestation can help, but it is time to stop suggesting there is a 'nature-based solution' to ongoing fossil fuel use,' noted Myles Allen, a professor of geosystem science at the University of Oxford. 'There isn't.'

The sharpest objections - which may also apply to BECCS - had to do with assumptions made about the type and quantity of land available for reforestation.

'It might sound like a good idea, but planting trees in savannahs and grasslands would be damaging,' Kate Parr and Caroline Lehmann from, respectively, the Universities of Liverpool and Edinburgh, commented recently in a blog.

The landscapes of lions, giraffes and vast herds of wildebeest cover more than 20 percent of Earth's land surface and can be as rich in biodiversity as tropical forests.

They are also home to a billion people, many of whom grow crops and raise livestock.

Andre Laperrière, Executive Director of Global Open Data for Agriculture and Nutrition, said: 'Our industrialised farming practices are in fact the largest contribution to soil erosion and pollution, and perhaps the biggest hurdle we face is to try and teach about half a billion farmers globally to re-work their agricultural model to be carbon sensitive.

'Other steps we can take would involve changing our collective diets to be environmentally ethical (avoiding mass produced, resource intensive and land pollutant foods such as avocados, palm oil and red meat), protect natural habitats and prevent largescale natural destruction (like in the amazon rainforest), improve crop varieties and engage in agri-forestry (instead of cutting down forests to farm).'