Comment on egusphere-2025-5436

Abstract. The Pliocene epoch, 5.33–2.58 Ma, is considered a key analogue for near-future climate scenarios, as it had atmospheric CO2 levels (>400 ppm) comparable to today and similar continental positioning. Understanding Pliocene climate evolution is also critical to establishing the conditions that enabled large ice sheets to form in the Arctic region during the intensification of Northern Hemisphere glaciation (iNHG) around 2.7 Ma. The causes of iNHG remain unclear, with hypotheses ranging from tectonic changes to CO2 reductions. Based on anomalous, pre-iNGH cooling signals recorded in a sea surface temperature (SST) record from Ocean Drilling Program (ODP) Site 1090, located in the southeastern Atlantic Ocean, studies have posited that early cooling of the already-glaciated Southern Hemisphere could have driven Earth’s climatic descent into the Pleistocene. Here, we provide an orbitally resolved alkenone-based SST record of ODP Site 1090 spanning the time interval ~4.3–2.6 Ma with improved laboratory protocols that significantly revises conclusions based on prior work. Our revised record of SSTs from ODP 1090 shows similar cooling trends to those found of equatorial and high latitude Northern Hemisphere sites, suggesting that a global forcing, such as a reduction in atmospheric CO2, prompted iNHG, as opposed to an early cooling of the Southern Hemisphere.