In fact, climate sensitivities above 6K trigger a global glaciation, or snowball Earth-something that has happened in the past, but not for over half a billion years.

Pierrehumbert, R.T. 2004: "High levels of atmospheric carbon dioxide necessary for the termination of global glaciation", Nature, 429, 646-649.

This freezing happened over 650 million years ago in the Pre-Cambrian, though it's now thought that there may have been more than one of these global glaciations.

When the currents weakened, possibly because their salt content was diluted at a critical juncture by fresh water from melting icebergs, a global glaciation began.

It is not clear whether this can be taken to imply a global glaciation, or the existence of localised, possibly land-locked, glacial regimes.

Although the boron variations may be evidence of extreme climate change, they need not imply a global glaciation.

Synthesised evidence has produced models indicating a "slushball Earth", where the stratigraphic record does not permit postulating complete global glaciations.

The million year long Gaskiers glaciation did not lead to global glaciation, although it was probably as intense as the late Ordovician glaciation.

There is evidence of multicellular life before that, in fossils of the deep ocean in the Ediacaran, which started at the end of the last global glaciation.

That pushes them very close to the end of the last global glaciation of the Cryogenian period, and makes them older than the rangeomorphs.