The Antarctic Circumpolar Current is the world’s strongest ocean current. This vast current system is linked to ocean overturning and is pivotal to the uptake of ocean heat and CO2. The strength of the Antarctic Circumpolar Current has varied across Earth’s past climates, but the exact drivers of this change remain elusive. Ocean models have not been able to adequately resolve eddies and dense shelf water formation processes that control current strength. Here, we assess a global ocean model which resolves such processes to diagnose the impact of future thermohaline and wind conditions on the Antarctic Circumpolar Current. This model suggests the strength of the Antarctic Circumpolar Current will decline by up to ∼ 20% by 2050. This decline is supported by simple scaling theory, and is driven by ice shelf melting, which weakens the density gradient historically supported by surface temperature. Such a decline in transport would have critical implications for the global ocean circulation, and hence, Earth’s climate system.