Land degradation is also a major contributor to mass human migration and increased conflict.
The dangers of land degradation, which cost the equivalent of about 10 per cent of the world's annual gross product in 2010 through the loss of biodiversity and ecosystem services, are detailed for policymakers, together with a catalogue of corrective options, in the three-year assessment report by more than 100 leading experts from 45 countries.
Produced by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the report was approved at the sixth session of the IPBES Plenary in this Colombian town.
The IPBES has 129 state members.
Sounding an alarm of serious danger to human well-being, the report says rapid expansion and unsustainable management of croplands and grazing lands is the most extensive global direct driver of land degradation, causing significant loss of biodiversity and ecosystem services -- food security, water purification, the provision of energy and other contributions of nature essential to people.
This has reached 'critical' levels in many parts of the world.
"With negative impacts on the well-being of at least 3.2 billion people, the degradation of the earth's land surface through human activities is pushing the planet towards a sixth mass species extinction," said Robert Scholes of South Africa, co-chair of the assessment with Luca Montanarella of Italy.
"Avoiding, reducing and reversing this problem, and restoring degraded land, is an urgent priority to protect the biodiversity and ecosystem services vital to all life on earth and to ensure human well-being."
"Wetlands have been particularly hard hit," said Montanarella.
"We have seen losses of 87 per cent in wetland areas since the start of the modern era - with 54 per cent lost since 1900."
According to the authors, land degradation manifests in many ways -- land abandonment, declining populations of wild species, loss of soil and soil health, rangelands and fresh water, as well as deforestation.
By 2014, more than 1.5 billion hectares of natural ecosystems had been converted into croplands. Less than 25 per cent of the earth's land surface has escaped substantial impact of human activity - and by 2050, the IPBES experts estimate, this will have fallen to less than 10 per cent.
"Through this report, the global community of experts has delivered a frank and urgent warning, with clear options to address dire environmental damage," said Sir Robert Watson, Chair of IPBES.
The IPBES report finds that land degradation is a major contributor to climate change, with deforestation alone contributing about 10 per cent of all human-induced greenhouse gas emissions.
Another major driver of the changing climate has been the release of carbon previously stored in the soil, with land degradation between 2000 and 2009 responsible for annual global emissions of up to 4.4 billion tonnes of CO2.
The report estimates that 50 million-700 million people will be forced to migrate by 2050.
"In just over three decades from now, an estimated 4 billion people will live in drylands," said Scholes.
"By then it is likely that land degradation, together with the closely related problems of climate change, will have forced 50 million-700 million people to migrate.
"Decreasing land productivity also makes societies more vulnerable to social instability -- particularly in dryland areas, where years with extremely low rainfall have been associated with an increase of up to 45 per cent in violent conflict," Scholes added.
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