If no unit is specified, it is Celsius, as that's the world standard.
Of course, we could read some context, but that would be too easy.
In December we had lows about 20/-7 and since the lows 45/+7 or warmer. Last weekend the elms and a quince started budding out. Trim, trim, etc. Last night and the next two, back to 20/-7. Then it warms up to 24/-5. Then back above freezing.
Those trees are now in the unheated garage.