Update: global harmonization of climate data since 1850 follows next.
"CLImatological database of World OCeans" was my first outing using Esri tools as personal project. I found this fabulous dataset with ¼ M points! Detailed here, it came from a 5 yr. EU project to scan captains ships logs for climate data in the 17-19th c. before weather data were recorded. Tall ships were mainly British, Dutch & French, Portuguese notably absent due to Lisbon archive destruction in the 1755 "Great Earthquake" (Wikipedia).