I think they’re saying that scientists said that the mummy had been exposed to air multiple times (followed by being frozen in ice) in the past (presumably not

I think they’re saying that scientists said that the mummy had been exposed to air multiple times (followed by being frozen in ice) in the past (presumably not attributed to Climate Change) but the last exposure which resulted in its discovery is attributed to climate change. The implication is that either lower case climate change is a periodic thing or else something doesn't follow.