Since this article is about Christians not worrying about the climate, I'll throw some Bible info into it.
1) The downward slope from above the 4 (4 thousand years ago, 2000 BC) that bottoms out at about 3,300 to 3,500 years ago (maybe 1500 BC) corresponds to the era of the Jewish patriarchs (Abraham, Isaac, and Jacob). Something to think about when reading the stories of shortages of food (i.e. Abraham and his nephew Lot having to part ways, the famine that Joseph managed as a ruler in Egypt). Ultimately that cooling period bottoms around the time of Moses's ministry.
2) From that point temps rise for centuries and top out around 11 century BC BC. This is called the Minoan Warm Period (not labeled in the graph, it's the red hump to the left of the Roman Climate Optimum). This rising of temps corresponds to the Era of Judges.
3) Where that tops off and goes back down is the Greek Dark Age cooling period, which corresponds to the Era of Kings. That bottomed out maybe 2nd or 3rd century BC.
4) The Roman Warm Period was going on during the time of Christ and the apostles (when the New Testament was written).