Connecting the ecological themes of Cloud Empress with the threat of an increasingly long and harsh winter definitely sounds cool. Perhaps even in some way caused by the chalk as a pollutant - directly or indirectly - or nature's defence against the polluters.
Having a worldwide yearlong winter would definitely sound like a campaign-defining feature to me, rather than a local adventure. So if that's not what you're going for you could try making it a more local meteorological phenomenon, perhaps with the threat of its expansion?
However you choose to go about it, I'm looking forward to see what comes out of it!