The report, compiled by 107 authors from 52 nations and released in Geneva on Thursday, noted humans typically relied on land for their homes and the great bulk of their food, fibre and feed for animals.
Mark Howden, director of the Climate Change Institute at the Australian National University and an IPCC vice-chair, said the report was “a warning flag” about the threats and “how hard we need to go” to cut greenhouse gas emissions.
Land’s effect on climate
About a quarter of the earth’s ice-free land was already subject to human-caused degradation, with soil losses as much as 100 times higher than soil formation, the report said.
Australia, sub-Saharan Africa and parts of east and central Asia were singled out as regions where rising evapotranspiration (caused by hotter temperatures and reduced rainfall) were causing deserts to expand.
Climate change would “ramp up” existing degradation, such as through erosion caused by more intense rainfall events, Professor Howden said.
But land would also affect the climate because land-clearing, methane from livestock, fertiliser, and other emissions related to farming and forestry are major sources of greenhouse gases.
“Just under a third of our emissions come from our food systems, globally,” he said.
‘Not safe at 2 degrees’
Andy Pitman, director of the ARC Centre of Excellence for Climate Extremes, said the thermal inertia of the oceans meant land warmed faster than the seas.
Where lands dry out, the cooling role of evaporation diminishes, so extreme temperatures are more intense.
“It’s why the 2-degree ceiling agreed in Paris [at the climate summit in 2015] isn’t safe,” Professor Pitman said. “Two degrees in the global mean [translates to] very, very sizeable amounts of warming in heatwave conditions over land.”
He cited farming regions such as Moree in northern NSW where last January’s average temperatures “slaughtered” previous records, beating the norm by close to 4 degrees.
“We’re seeing those extreme temperatures rapidly rising in part because in some regions we’re seeing a drying,” Professor Pitman said.
Australia has warmed about a degree in the past century, and the Bureau of Meteorology says day-time temperatures were both the hottest on record in the year to June and for the first seven months of this year.
Average soil moisture for the 12 months to June 30 were also the lowest on record at just 8.5 per cent for the top metre. That beat the record low of 8.7 per cent 1914-15 and compared with an average of 12 per cent, the bureau said.
The IPCC report said warming, changing precipitation patterns and the greater frequency of some extreme events “has already affected food security”.
“Changes in climate can amplify environmentally induced migration both within countries and across borders,” the report said, adding increased displacement and threatened livelihoods may “contribute to exacerbated stresses for conflict”, it said.
Alana Mann, a lead researcher at the Sydney Environment Institute, said the report should be “a big wake-up call”, not least for the cities where people “assume supermarket shelves will always be full”.
Dr Mann said the report also highlighted how land management had to be brought back closer to what the environment could sustain.
“All of [excessive extraction] is about driving production of food at the expense of the environment,” she said.
The report noted populations could increasingly be exposed to wildfire as temperatures over land increase.
“Across the globe, we’re seeing both changes in the intensity and seasonality of fires … that’s happening in Australia as well,” Professor Howden said. “The projections are for those issues associated for fires to increase.”
Richard Thornton, chief executive of the Bushfire and Natural Hazard CRC, said authorities in Australia were preparing for another above-average fire season for much of the country.
“The evidence is all piling up from a hazards perspective,” Dr Thornton said. “The future doesn’t look like the past.”
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.