During the mid-Miocene (~16 to 14 million years ago), Earth was much warmer with CO₂ levels similar to what is expected for our future. Here, we perform simulations with a new geography of the mid-Miocene, which include changes in ice coverage, land and sea distribution, solar energy and CO₂ concentrations. Despite high CO₂ concentrations, our mid-Miocene is too cold compared to geological reconstructions, but shows great potential to understand future climate change and its sensitivity to CO₂.