Is this market resolved according to this comment, i.e. there has to be at least one week during which population decreases, or does population have to decrease over the whole year?

@StevenK Yes, although since I think this has to be clearly due to a massive disaster on an unprecedented scale, on the off chance that counters are not available (perhaps out of respect to the dead?) and Manifold is still up, I may use broader calculations than a simple counter. E.g., confirmed news stories of "two million dead due to that nuclear war last week" might trigger a resolution. (I would double-check all numbers used in that calculation before resolving though; 2 million a week is a rough guesstimate).