I've been looking at some sediment core data from the North Atlantic — it shows a pretty clear cooling trend from around 5,000 years ago to the past few hundred. The cooling seems to align with decreased solar activity and changes in ocean circulation. It's not a steady drop, but the overall direction is downward. The last few centuries, of course, have been an anomaly due to industrialization. But the long-term pattern still holds. [Source](https://www.nature.com/articles/s41586-020-2671-1)