The ranking methodology utilized by Greenpeace and Newsweek are radically different; the Newsweek rankings are based on a holistic view of the companies including greenhouse emissions, water consumption and supply chain management. Greenpeace study analyzes more focused benchmarks like the use of toxic chemicals.
Greenpeace's biggest knock on HP is it's continued polyvinyl chloride (PVC) and brominated flame retardant (BFR) usage despite a commitment to discontinue their utilization, while Newsweek recognizes their continued use— they give HP credit due to progressively diminished usage.
HP got especially high marks for it's Green Policy and Performance from Newsweek, issues Greenpeace did not consider. While Newsweek's ranking system is more comprehensive, there is good reason Greenpeace looks specifically at PVC and BFRs. Dioxin, an organic compound, produced as a byproduct of PVC production has been implicated in a broad range of health problems from acne to sarcoma.
Thanks Prof. Singaram for helping me work through organic chemistry.