National Oceanic and Atmospheric Administration
https://psl.noaa.gov/gcos_wgsp/Timeseries/Data/nino34.long.data

National Oceanic and Atmospheric Administration
https://www.ncei.noaa.gov/products/extended-reconstructed-sst

National Oceanic and Atmospheric Administration
https://www.ncei.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.pdo.dat