Studying the Pliocene (5.33–2.58 Ma) is key to understanding Earth’s climate under current atmospheric CO₂ levels and the development of permanent Northern Hemisphere ice. We used ocean sediments and improved laboratory methods to reconstruct sea surface temperatures from Ocean Drilling Program Site 1090 (south Atlantic) from ~4.3–2.6 Ma. Our data suggests cooling patterns similar to those found worldwide, suggesting a global forcing, like decreased CO₂, triggered the shift to the ice ages.