This is probably my favourite phrase.
It has this beautiful, Stapledonian sense of sheer scale: summing up going on a fifteen thousand year span of time, containing the whole story of our race, from the last days of the protohuman apes of the Old Stone Age, into the Mesolithic dawn of humanity, the rise of language, agriculture, civilisation, bronze, iron, steel and silicon, from the Lascaux cave paintings to maps of the universe in a single phrase which ignores all of them in favour of a broad description of what the weather was like. And you know what? It's not missing the point - the temperature mattered; the rest of that stuff was detail.
As well as looking back at the past, it implicitly says something about the future: there will be future interglacials, and before we get there, there are going to be more glacials. People tend to forget that; when they think about the future, an ice age typically isn't part of the picture. Nonetheless, it's out there, waiting to happen.