| TLDR: Data sources include ships at the time that made records of temperatures as they traveled; coastal weather-stations kept pressure records indicating how strong the big weather pattern was; biological indicators from tree-ring growth, coral formations, and changes in agricultural output. _________ I found a NOAA paper about the 1877 El Nino [0] and here are two quotes with lengthy references omitted: > The existence of the strong 1877/78 El Niño event is supported by in-dependent data sources other than [Sea Surface Temperature], such as the Southern Oscillation index derived from sea level pressure, the drought indices derived from tree rings and corals, and records of famine or food production around the world. > [...] However, there were few in situ [Sea Surface Temperature] observations at that time. [...] These
sparse [Sea Surface Temperature] records in the east-central Pacific were measured during 14–31 December 1877 and provided by Deutsche Seewarte Marine (ship ID 120) and Met Office Marine Data Bank (ship IDs 4238 and 4270). IANAClimatologist and I can't guarantee that's exactly the research that went into the Washington Post article cited by the substack post... however I think it's "good enough" for your question about methods. P.S.: While I'm usually a "data is toxic" person when it comes to private data and surveillance, this kind of data is the polar opposite: It's amazing when humdrum daily information becomes useful to someone decades later, and I can only hope we continue "paying it forward" with similar gifts to those who will come after us. They are literally irreplaceable, without some form of time-travel. [0] https://repository.library.noaa.gov/view/noaa/46581 |