Varian considers the Nordhaus and Dasguptha critiques of the Stern Review in Recalculating the Costs of Global Climate Change. Here is the conclusion:
... the choice of an appropriate policy toward global warming depends heavily on how one weighs the costs and benefits it imposes on different generations. The Stern Review chose a particular way to do this, but many other choices could have been examined.
Exploring the implications of alternative assumptions is likely to lead to better policy than making a single blanket recommendation. At least at this stage of our understanding, exploration beats exhortation.
In other words, choosing a 0.1% discount rate and sticking to it is inappropriate.