Climate change could cause severe crop losses in South Asia and southern Africa over the next twenty years, a study in the journal Science says. The findings suggest southern Africa could lose more than 30% of its main crop, maize, by 2030.

In South Asia losses of many regional staples, such as rice, millet and maize could top 10%, the report says. The effects in these two regions could be catastrophic without effective measures to adapt to climate change.

The majority of the world’s one billion poor depend on agriculture for their livelihoods. Yet, said lead author David Lobell, it is also “the human enterprise most vulnerable to climate change.”