Is GWP20 relevant?

At the 31st Open Ended Working Group of the Montreal Protocol meeting in Montreal in August 2011, a paper proposing to calculate GWP figures on a 20 rather than on a 100-year basis was released.
Authored by Janos Maté, veteran Greenpeace campaigner and David Kanter (PhD candidate at Princeton University), it draws from research by German consultants Öko-Recherche GmbH and HEAT GmbH and attempts to make the case that “policies based on GWP20 values of HFCs highlight the benefits of climate action more accurately”.
Greenpeace argues that the average lifeline of HFCs in use today is 21.7 years, which makes the 20 year metric better-suited. For instance, using GWP20 would redefine “low GWP” substances: as an example HFC-32, which has a GWP of 675 over 100 years, would have a GWP of 2330 over 20 years. According to IRHACE, this could lead to HFCs being taxed according to their climate impact across their atmospheric lifetime.