WGI
Also: WG1, 'Working Group I', 'Working Group1'
IPCC Working Group I
Working Group I produces the section of the IPCC reports describing the 'Physical Science Basis' for our understanding of Anthopogenic Climate Change - why it is happening.
Definition based on (revised from) IPCC AR4.
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.