The United Nations (UN) projects that the global population will zoom from approximately 7.1 billion people today to 9.6 billion people by 2050. The World Bank and U.S. Census Bureau expect it to reach 9.4 billion. Other models suggest anywhere from 8.3 billion to 10.9 billion souls on the planet by 2050.

These models “assume a no-surprise future and focus on three main drivers of population — births, deaths and migration. Life expectancy is kept on a consistent upward trend, and unpredictable events like epidemics and wars are ruled out,” National Geographic explained in its population update this year.

In other words, the population forecasts that all policymakers around the world use are based on existing trends, not resources or surprise events.

But those who look at population through the lens of resources come to very different conclusions about population growth.