The amount of farmland around the world that will need to be irrigated in order to feed an estimated global population exceeding 9 billion people by 2050 could be up to several billion acres, far higher than scientists currently project, according to a new study by Princeton researchers. The result would be a far greater strain on aquifers, as well as the likely expansion of agriculture into natural ecosystems as farmers search for water.

Existing irrigation models — which are widely used to define policies on water and food security, environmental sustainability, and climate change — suggest that the amount of agricultural land requiring irrigation could extend between 590 million to 1.1 billion acres during the next 30 years. But those projections likely underestimate population growth and too confidently assume how much land and water will be available for agriculture without having to find new sources.

The amount of irrigated land could in fact increase to as high as 4.4 billion acres, which is enough land to cover all of South America. The researchers urge policymakers to acknowledge that much more irrigated land may be required in order to avoid underestimating the potential environmental costs and more accurately plan for future food needs.