Western boundary current (WBC) extensions such as the East Australian Current (EAC) southern extension are warming 2–3 times faster than the global average.  Among WBCs, the EAC has a more energetic eddy field relative to its mean flow. However, the mechanisms responsible for the enhanced warming over the EAC extensions are still debated. Here we show that barotropic instabilities are the primary source of eddy kinetic energy (EKE), and they control EKE variability in the EAC system. The ocean warming variability in the EAC is associated with the formation of anticyclonic eddies.  Enhanced eddy generation in the EAC extensions through changes in barotropic instabilities results in enhanced ocean warming as the eddies propagate. This results from a poleward shift of the EAC, associated with changes in the mid-latitude easterly winds. Consequently, the EAC have penetrated poleward but not strengthened and are now transporting more heat into their extensions. Our study clearly elucidates the dynamic processes driving increased eddying and warming in the EAC extensions and has implications for understanding and predicting ocean warming, marine heatwaves and the impact on the marine ecosystem in the WBC extensions under climate change.

西边界流,中尺度涡,海洋变暖