US. federal policy defines plagiarism as follows:
Plagiarism is the appropriation of another person’s ideas, processes, results, or words without giving appropriate credit.
Here is a discussion of the topic from Penn State, where Michael Mann of Steig et al has an appointment.
In an entirely unrelated development, Steig et al have issued a corrigendum in which they reproduce (without attribution) results previously reported at Climate Audit by Hu McCulloch (and drawn to Steig’s attention by email) – see comments below and Hu McCulloch’s post here.
They also make an incomplete report of problems with the Harry station – reporting the incorrect location in their Supplementary Information, but failing to report that the “Harry” data used in Steig et al was a bizarre splice of totally unrelated stations (see When Harry Met Gill). The identification of this problem was of course previously credited by the British Antarctic Survey to Gavin the Mystery Man.
Update: Pielke Jr picks up the story here
Here is a corrected version as calculated by RomanM below.