We have, or rather scientists have a very good record of past climate data going back a couple of million years.
Our best clues are from the pattern of climate change which has occurred during the present Holocene as a continuation of the Pleistoscene geological periods. Snow buried WW2 aircraft are no help whatsoever in determining the overall scientifically determined pattern of climate oscillations.
It was the Swiss researcher Louis Agassiz who first determined that there had been an ice age back in the middle of the 19th century. This despite the popular certainty that there had been a global flood. He showed evidence for his hypothesis which eventually was accepted. Later researchers showed that there was not just one ice age but four ice ages, this early 20th century idea also had evidence but it was the deep sea sediment cores from the Pacific mainly, which told the whole story. Arctic ice core information amongst others corroborated the sediment cores.
By the end of the 1980s, earth science had all the data to show the slow 'tide' of ice advance and retreat over the polar regions was due to the relative positions of the Earth and sun in their periodic changes of position. They 'wobble' with a periodicity having maximum effect relative to the amount of incoming solar radiation from max. to min. during an epoch of just over 100,000 years.
This last climate minimum (full on ice age) was between 20,000 to 18,000 years ago followed by global warming and pluvial period up to the present interglacial maximum which has been around for ten thousand years and might last another ten to fifteen thousand years.
The evidence for climate history is built up from dozens of types of sources in hundreds of thousands of locations. The faunal assemblages, the floral, the insects, the pollen, river life, river and lake deposits (varves), yes ice cores and dozens of types of other more esoteric data all add up to a real knowledge of what climate existed in the past.
There is not the slightest evidence that the Biblical flood could have ever happened but there is evidence to the contrary that it did not happen.