This doesn't make sense: "With summertime temperatures typically -10°C to -20°C". Maybe the negative was mistakenly added, and nobody noticed in editing? 10°C to 20°C would be reasonable for a "forested and grassland plateau".

There was an ice sheet starting just north of this area, it would have melted at 10°C.

it's reinforced in the same sentence after you cut off your quote and is repeated again further into the article:

> Nash said the caves would have been "quite a cosy place to live, especially compared with the -20°C outside".

It is, but the number is still strongly disagreeing with any other value I can find reference to so GP does seem to be on to something being off with this reporting.

My best bet is perhaps "summer" and "winter" got swapped? That's a simple single word mistake and -10 C would seem to be about the winter average in Ireland during the last ice age from other sources I can find, regular dips to -20 C at night or particularly cold days would seem quite reasonable. Based on any other sources I can find, thea peak of summer should have been slightly warmer than freezing (which is not incompatible with year round glacial coverage, it takes a lot of energy to melt such enormous volumes of ice).

I've sent Dr Nash a short email asking if that section of the article was accurate in hopes he's willing to clarify one way or the other.

Agreed, that jumped out at me also. Those numbers make no sense

So this would suggest that the Goidelic languages (Irish Gaelic, Scottish Gaelic, Manx) are derived from the Brittonic languages (Welsh, Breton, Cornish). [1]

I wonder how this affects the different proto-Celtic to modern Celtic languages hypothesis. [1]

This would suggest the following language tree: Breton -> (Cornish / Welsh) -> Irish Gaelic -> (Manx / Scottish Gaelic).

[1] https://en.wikipedia.org/wiki/Celtic_languages

This migration predates the arrival of Celtic speakers by many thousands of years.

There were no Brythonic languages 15,000 years ago.

What are you talking about?