We assess the insurance infrastructure needed to support hundreds of millions of African farmers facing climate-driven agricultural losses. Using household survey data from hundreds of thousands of farms and CMIP6 climate projections, we find annual payout needs will more than triple from 2.3 million farmers today to 8.7 million by 2050, with 174 million requiring support over two decades. Without urgent adaptation investment, millions will lose over half their income annually to extreme weather, risking an unprecedented humanitarian crisis.