UK fans... Years of Living Dangerously IS airing on UK National Geographic. I just found it on Tuesday at 10pm (I'm on Virgin Media which is channel 266).

This week's episode is David Letterman which is Ep1 and Josh is Ep5, so I'm guessing that should make it 20th December when his airs. Hope it doesn't get bumped because it's Christmas week!
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EDIT - Just checked Nat Geo UK website and it IS scheduled to air on 20th Dec at 10pm - set your recorders Josh fans.