The two concepts at work here are conservation of matter and the question about many surfaces vs. fewer surfaces absorbing heat. You may wonder what this story is doing in the Earth system science area, but it has to do not only with thermodynamics and conservation of matter but with water, arguably the most important material on the planet. It sounds more like a physics story but the author suspects that more integration of the various sciences is done in Earth science than in any other of the disciplines because it uses so many concepts from other areas in order to understand its overarching view of the world we live in.