Sea-surface temperatures during the last interglaciation period were like those of today, a new study reports. The trend is worrisome, as sea levels during the last interglacial period were between six and nine meters above their present height. The last interglaciation (LIG), which occurred 129,000 to 116,000 years ago, is thought to have been about as warm or a bit warmer than today, making it a useful reference to validate global climate models and understand sea-level response to a warming climate. Here, Jeremy S. Hoffman and colleagues compiled 104 published LIG sea surface temperature (SST) records from 83 marine sediment core sites. They compared each core site to data sets from 1870-1889 and 1995-2014, respectively. Their analysis reveals that, at the onset of the LIG 129,000 years ago, the global ocean SST was already similar to the 1870-1889 average. However, by 125,000 years ago, the global SST increased by 0.5° ± 0.3°Celcius, reaching a temperature indistinguishable from the 1995-2014 average. These results suggest that LIG global mean annual SSTs simulated with most global climate models are too low. As well, the data show that the Atlantic Ocean in the Northern Hemisphere was cooler at the beginning of the LIG, compared to temperatures in the Southern Hemisphere. Collectively, these results may help scientists better understand how oceans will respond to modern warming.