Geneva: Humanity faces increasingly painful trade-offs between food security and rising temperatures within decades unless it curbs emissions and stops unsustainable farming and deforestation, a landmark climate assessment said Thursday.
The UN's Intergovernmental Panel on Climate Change (IPCC) warned that 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.
Its report on land use and climate change highlighted the need to protect remaining tropical forests as a bulkhead against future warming.
But it offered a sobering take on the hope reforestation and biofuel schemes alone can offset mankind's environmental damage.
It cautioned that these mega-projects could endanger food security, underlining that reducing emissions will be central to averting disaster.
"This is a perfect storm. Limited land, an expanding human population, and all wrapped in a suffocating blanket of climate emergency," said Dave Reay, Professor of Carbon Management at the University of Edinburgh.
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.
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.
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.
"Land is where we live," IPCC co-chair Hoesung Lee said during the report's launch Thursday.
"Land is under growing human pressure and land is part of the solution, but land cannot do it all." The IPCC is the world's leading authority on climate change. Last year it warned that limiting global warming to 1.5 degrees Celsius -- the optimal level aimed for in the Paris climate deal -- would be impossible without a drastic drawdown in greenhouse gas emissions.
The land use report warned that any delay in reductions -- across industry, transport, agriculture and infrastructure -- "would lead to increasingly negative impacts on land and reduce the prospect of sustainable development".
It also 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.
Bioenergy in the form of vegetation used to sequester carbon also has potential. But room for that must be carved from crop land, 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." Linda Schneider, senior programme officer of International Climate Policy at the Heinrich Boll Foundation, told AFP the report left "no doubt about the devastating impacts large-scale bioenergy and afforestation would have on water availability, biodiversity, food security (and) livelihoods." The 1,000-page report takes a deep dive into the systems we use to feed ourselves, and the devastating impacts they are wreaking.
Not only does agriculture and its supply lines account for as much as 37 percent of all man-made emissions, current industrialised production and global food chains 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.
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.
"Some diets require more land and water and lead to higher emissions than others," said IPCC co-chair Jim Skea.
"We don't do recommendations, we produce the evidence." 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 of warming the risk of food insecurity ticks over to "very high".
"There are solutions in the hands of farmers. But there are also solutions in the hands of each of us, when we buy food, and don't waste food," Masson-Delmotte added.