From the GISS FAQ: https://data.giss.nasa.gov/gistemp/faq/index.html#q202 https://data.giss.nasa.gov/gistemp/faq/index.html#q202 > Q. Why does GISS show no da

From the GISS FAQ: https://data.giss.nasa.gov/gistemp/faq/index.html#q202 https://data.giss.nasa.gov/gistemp/faq/index.html#q202 > Q. Why does GISS show no data from before 1880? > A. The analysis is limited to the period since 1880 because of poor spatial coverage of stations and decreasing data quality prior to that time. Meteorological station data provide a useful indication of temperature change in the Northern Hemisphere extratropics for a few decades prior to 1880, and there are a small number of station records that extend back to previous centuries. However, we believe that analyses for these earlier years need to be carried out on a station by station basis with an attempt to discern the method and reliability of measurements at each station, a task beyond the scope of our analysis. Global studies of still earlier times depend upon incorporation of proxy measures of temperature change like tree rings, ice core data, etc.