| The claims Hansen made are contained in his research papers. So you'd have to cite them, though in most of the papers I've read they tend not quote absolute numbers. In https://pubs.giss.nasa.gov/docs/2010/2010_Hansen_ha00510u.pd... paragraph 6: """
6] One consequence of working only with temperature change is that our analysis does not produce estimates of absolute temperature. For the sake of users who require anabsolute global mean temperature, we have estimated the 1951–1980 global mean surface air temperature as 14°C with uncertainty several tenths of a degree Celsius. That value was obtained by using a global climate model[Hansen et al., 2007] to fill in temperatures at grid points without observations, but it is consistent with results of Jones et al.[1999] based on observational data. The review paper of Jones et al.[1999] includes maps of absolute temperature as well as extensive background information on studies of both absolute temperature and surface temperature change.
""" The 2007 paper is https://pubs.giss.nasa.gov/docs/2007/2007_Hansen_ha09210n.pd... Jones' paper https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999... Section 6 discusses the anomaly vs absolute temp. https://core.ac.uk/download/pdf/19595636.pdf Introduction gives a brief history and list of the historically calculated values. So he was probably using the best value they had at the time. I don't know why any specific number was printed in the popular press at any given time though. The 90's "pause" is still reflected in the data (depending on how you long you want to average over), then temps started increasing again. |