Barring urgent action, land degradation that already has affected the lives of two-fifths of humanity will worsen, reducing crop yields and increasing social instability, nearly 100 scientists from 45 countries warned in a report released on Monday.

Worsening land degradation is driving the extinction of species and intensifying climate change in addition to ratcheting up mass human migration and increasing conflict, said the world's first comprehensive assessment of land health.

The three-year assessment was produced by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, a global scientific group founded in 2012 that has 129 members.

The report said the direct driver of land degradation is rapid expansion and unsustainable management of croplands and grazing areas. The deterioration is also driven by the "high-consumption lifestyles" in the most developed economies.

"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," said Robert Scholes of South Africa, co-chair of the assessment.

Currently, land degradation is reducing the annual global gross product by 10 percent due to a loss of biodiversity and ecosystem services, the IPBES report said.

Every 5 percent loss of gross domestic product is associated with a 12 percent increase in the likelihood of violent conflict, the report warned.

In a little more than three decades from now, an estimated 4 billion people will live on dry lands, it said.

"By then it is likely that land degradation, together with the closely related problems of climate change, will have forced 50 million to 700 million people to migrate," Scholes said.

It said that by 2050, the combination of land degradation and climate change could reduce global crop yields by an average of 10 percent and by up to 50 percent in some regions.

The report found that higher employment and other benefits of land restoration often far exceed the costs involved.

On average, the benefits of restoration are 10 times higher than the costs, and for regions like Asia and Africa, the cost of inaction is at least three times higher than that of action.

"Fully deploying the toolbox of proven ways to stop and reverse land degradation is not only vital to ensure food security, reduce climate change and protect biodiversity, it's also economically prudent and increasingly urgent," Montanarella said.

IPBES Chairman Robert Watson said: "Of the many valuable messages in the report, this ranks among the most important: Implementing the right actions to combat land degradation can transform the lives of millions of people across the planet, but this will become more difficult and more costly the longer we take to act."