since one of my breeding survived and i did this 48hour torture with just fireplaces i want to share my experience, maybe someone can find some usefull information in this http://prntscr.com/mc1jbo
TDLR: for cooling down i found out that on a certain level of high, the temprature jumps 5°C down, so if u dont want to leave ur island and it has kinda hotish weather, u have to build a lift /tower far up. :x On the mountain i was breeding, it was normaly around 6-12°C, meanwhile on ground 16-22°C , on a heatwave the temprature even went up on the mountain to over 20°C, wich was death sentance on one of my cubs :c so i will build a tower on this mountain to have another 5°C less temprature.
PS: i know my english is horrible xD