> “Given the large climatic changes seen in the early 19th century, it is difficult to define a pre-industrial climate,” explains lead author Stefan Brönnimann, “a notion to which all our climate targets refer.” We shouldn't even by trying to "target" a global temperature. That's nuts. But if we were going to choose an ideal temperature, it would be that of the Roman period, which was nice and warm -- much warmer than it is now.