 20CR has been described as providing independent “observational” confirmation of the twentieth century warming seen in station-based datasets (Compo et al. 2013). More generally, despite the central role of computer forecasts in reanalysis, many climate scientists refer to reanalysis data as “observations” and use them as such: to investigate climate system dynamics, to evaluate climate models, to find evidence of the causes of recent climate change, and so on. Other climate scientists, however, emphasize that reanalyses should not be confused with “real” observations (e.g., Schmidt 2011). Parker (2017) argues that differences between data assimilation and traditional observation and measurement are not as great as one might think; she suggests that data assimilation can be understood as a complex measuring procedure that is still under development.