Thanks for posting it.
Love the tiny green mark that designates the Thermometer Era.
Also, there have been three distinct kinds of thermometers used since the 1850s, and no clear way to distinguish how the 1-2 degree F measurement variation between them should be resolved in the historical record.
Also, most developed countries with extensive contemporary temperature stations use airport temperatures to calculate the average temperature.
The reason is valid - the exact temp at an airport is vital safety information for pilots.
Unfortunately, this hugely exaggerates the Heat Island effect, especially at night, when compared to lower temps just a couple miles away from the airport.
You and I could spend all day talking about temperature reading inaccuracies. IMHO some of it is deliberate (i.e. setting up thermometers near HVAC units).
When looking at pre-temp recording history, I prefer to look at proxy measurements but not like the left does (i.e. tree rings). I look at things we know from history.
For example, in my graph know that the city of Ephesus (Bible readers know it as the city Paul wrote the letter Ephesians to) was a port city beginning at about 1100 BC (top of the Minoan Warm Period in my graph, which is the red hump to the left of the Roman Warm Period). (Addendum, the Minoan Warm Period almost exactly corresponds to the Era of Judges from Moses to Samuel.) That Ephesus was a port city IMHO is an indicator of sea levels at the time. Then when the Greek Dark Age cooling period began (corresponding to the Era of Kings after the Jews demanded Samuel anoint them a king), the sea levels lowered enough to move the coast away from Ephesus. Amazingly, unlike other port cities Ephesus dug a canal out to the sea so that their city could continue acting like a port city. This gave them the can-do reputation (much like the prestige the U.S. got after putting a man on the moon). Then the Roman Warm Period (time of Christ) raised the sea levels and the canal for connecting Ephesus to the coast still existed, but was shorter. Then the Dark Age (roughly AD 300 to 900, depending on who you ask) lowered the sea levels and moved the coast so far out that Ephesus could no longer maintain its port city status. The Medieval Warm Period raised the sea level, but the Little Ice Age moved the coast many miles away from Ephesus. Today, the Modern Warm Period has raised the sea levels, but the coastline near Ephesus is still miles away from the ruins of Ephesus.
This is a data point suggesting that the Modern Warm Period's raising of the sea level isn't as warm as what was the norm back when Paul wrote the letter to Ephesians. The same with Pevensey Castle in the UK during the Medieval Warm Period being on the coast and sometimes having boats tie to the castle, plus a notorious history of drowning prisoners by putting prisoners in the ground floor when the tide was out, knowing it was a matter of time until they drowned when the tide came back in. Today, if they used the castle to drown prisoners they'd have to pipe in the water because the coastline is a mile away. LOL That's another historical data point suggesting that the Modern Warm Period ain't as hot as what was the norm in the Medieval Warm Period.
Then there's the fact that the warm periods are the good times to be alive (higher crop yields, more predictable rain patterns, less deaths by plague). There are more atrocities committed during the cooling periods while everybody is struggling to survive.