Each year, the planet has to feed more hungry, hungry humans. Right now, projections suggest that we might just be able to meet the challenge of feeding our growing population in 2050, but only if we make better use of the land that we use for agriculture.

For sub-Saharan Africa (SSA), though, the question gets a little more complicated. Even if there’s enough food globally to go around by 2050, will SSA be able to produce enough to be self-sufficient? A paper in this week’s PNAS suggests that the region might be stuck relying on imports unless it massively expands its croplands. This would be bad news for the environment, and it wouldn’t be easy.

Every region on Earth relies on food imports to some extent, but importing large amounts of food is only really feasible in countries that are economically developed. For developing countries, affording large quantities of food imports can stifle economic development. Right now, SSA produces around 80 percent of the staple grains that it needs. By contrast, North and South America, Europe, and Australia all produce well above 100 percent of their own needs. And the population of SSA is projected to increase more than that of other regions.

To avoid having to import even larger amounts of food in the future, SSA would need to make better use of its agricultural land so that the yield of the land gets closer to its theoretically possible maximum. For the region to achieve its maximum, SSA must optimize its use of water, nutrients, and disease and pest control.

But, if SSA checks every box on that list, will it be able to feed itself in 2050? To find out, the authors of the paper looked at 10 countries as a test case. These countries together had 58 percent of SSA’s arable land in 2010, making them relative agricultural powerhouses. Their average production for the five main grains that they rely on—maize, millet, rice, sorghum, and wheat—is 83 percent of what they need, which is similar to the continent as a whole.

The 10 countries also housed 54 percent of SSA’s population in 2010, and their estimated food demand is set to more than triple by 2050. Assuming that actual production from farms reached 80 percent of the theoretical maximum potential (and that’s a pretty generous assumption given that, in some cases, it’s only at 20 percent now), some countries would be able to produce more than 100 percent of their own needs. Region-wide, however, the average would still be below 100 percent.

But that’s just based on currently farmed land—what if more land were used? If yield gaps were to continue closing at their current, very slow rate, the region would need to increase the agricultural land currently used for grains by an alarming 185 percent. Quite simply, there isn’t enough land for this in seven of the 10 test case countries. Agricultural expansion on this scale would also mean worrying things for biodiversity and greenhouse gas emissions.

A particularly sticky point that the researchers raise is how generous many of their assumptions are. For instance, their land expansion estimate assumes that all of the new agricultural territory would be of the same quality as existing land. Yet, much of the best land has probably already been used, so any new land is likely to be lower quality. The researchers also haven’t factored in a changing climate or the social and political changes that would be needed to support closing the yield gap.

There’s one point of optimism, though: none of these estimates account for possible progress in genetic engineering that might improve yield potential. With modern farming methods and ongoing research, making substantial progress on closing the current yield gap should be possible. But modernization and research on their own won’t be enough. SSA will need to intensify what it can get from the land using new technology or else face expanding its land use, relying on imports, or both.

PNAS, 2016. DOI: 10.1073/pnas.1610359113 (About DOIs).