Really cool and interesting visualization. Since this is most likely a common chart for people looking at climate change and it may be explained by the parents

Really cool and interesting visualization. Since this is most likely a common chart for people looking at climate change and it may be explained by the parents feedback, I was wondering if anyone knew what shades are held in reference to? Are they being compared to the average temperature of the last century, average compared to 1849, or whether its sort of a running diff to the previous year?