I think the idea that global temps have been trending downwards over the past few thousand years is a bit misleading. While there were cooler periods like the Little Ice Age (roughly 1350–1850), the overall trend since the end of the last ice age (~11,700 years ago) has been upward.
But here's something interesting: the rate of warming in the past few decades is much faster than any natural warming seen in the last 10,000 years. For example, a 2019 study in *Nature* (https://www.nature.com/articles/s41586-019-1084-x) looked at temperature reconstructions and found that the current warming rate is unprecedented in the Holocene.
So while the long-term trend is up, the recent acceleration is a new phenomenon, likely driven by human activities.