text: Over land, near-surface? air temperatures are those commonly measured about 1.5 to 2.0 meters above the ground level at official weather stations, at sites run for a variety of scientific purposes, and by volunteer (cooperative?) observers . These stations often experience relocations, changes in instrumentation and/or exposure (including changes in nearby thermally emitting structures), effects of land-use changes (e.g., urbanization), and changing observing practices, all of which can introduce biases into their long-term records. These changes are often undocumented.