The Climate.gov article Nature’s archives: piecing together 12,000 years of Earth’s climate story by Alison Stevens (4/15/2020) provides an overview of paleoclimate proxies and links to a new database of these records.
Paleoclimate proxies indirectly record climate and atmospheric conditions present when they formed or grew; air bubbles in ice cores sample past carbon dioxide levels, pollen and undecayed plant matter reveal growing conditions, and the ratio of oxygen isotopes in marine fossils indicate ocean temperatures. Proxies can come from all over the world — from glaciers in Antarctica to the tropical oceans — and compiling them into datasets can help place today’s warming climate into the context of a longer history.
The article links to the Nature post A global database of Holocene paleotemperature records with the data source at NOAA’s Temperature 12k Database.