A United Nations report Monday found that more than three quarters of the world’s land became permanently drier in the last 30 years, with rising temperatures and climate-change induced drought escalating the problem. The study was released as global delegates met at the COP16 summit on desertification in Saudi Arabia’s capital Riyadh.

Led by the UN Convention to Combat Desertification, the summit aims to restore 1.5 billion hectares of desertified land by 2030, and is seeking $2.6 trillion in investment to restore salvageable land and protect at-risk regions from degrading.

“This analysis finally dispels an uncertainty that has long surrounded global drying trends,” a UNCCD representative said, adding that desertification and the subsequent loss of arable land represents an “existential threat affecting billions around the globe.”

Some 2.3 billion people live in expanding drylands, the report found, with South Sudan, Tanzania, and China being the countries most affected.