The data presented here has been constructed from thousands of surface station measurements from around the world, and tends to be a couple hours behind real - time. (berkeleyearth.org)
Unlike the ground weather station measurements, these sample the entire world evenly, and sample at several heights in the air. (climate-skeptic.com)
We have temperature station measurements in 1940 to estimate the 1940 temperature, and data since then to estimate the warming trend. (skepticalscience.com)