Humans require a pretty particular ratio of CO2 in their atmosphere.
Plants use oxygen to live, and only become net producers of oxygen when they're photosynthesizing.
If the sunlight were cut off to, say Earth for example, would humans, animals (and plants, I don't have good numbers for their sensitivity to CO2 - but they are sensitive to some degree) choke on the raising CO2 levels before freezing to death?
How long would it take to raise the CO2 levels to various thresholds? Obviously once you start killing off life you'll end up with less CO2 pollution, so at some point you'll level off the CO2 ratio.
Any idea of what a choked planet's atmosphere would look like?