Actually, we can, because they would have physical effects that would leave evidence.
the christian faith is one of the only places where there is this weird.. coexistence of logic and miracles sharing time and space like Schrodinger's cat, alive and dead at the same time, waiting for someone to open the scriptures and choose their own interpretation.
I once got excited when i calculated that it might be possible to speed up the earth's rotation if you were to suspend 600 feet of water above the atmosphere and then have it all come crashing down.. from 360 days per year to 365.. but if you were to do that, the earth would be boiled alive and nothing would survive. but.. "God works miracles" --yes, but why would God send a flood one time, and an angel of death another? why not just send the black plague (of which many other plagues may have wiped out 30-60% of the earth many times before)
(even just increasing the rotation from 365 to the current 365.24xxx would boil everything) but, since creation was alledgedly perfect, why did God pick an irrational number for the days in a year?)
my sister had a dream showing her the flood was a local event in the middle east and the reason why was because God was sick of their child sacrifice. she had that dream when she was still a christian, yet had concerns about what was taught. perhaps my mom's homeschooling taught us critical thinking skills.. turns out both my sister and two younger brothers all knew the worship lyrics were theologically inaccurate, and woefully so!
anyhow, as many others have shown, all cultures have a flood myth, which Graham hancock has showed fairly well that it corresponds to the ice age of 12000 years ago. as such, anyone who had prophetic knowledge and convinced their tribe to move ahead of a catastrophe (whether drought or water) would have been regarded as a hero and the stories would be passed down.
yes the ice and flooding was global, but not all at the same time, otherwise we would not have the diversity of dna that we have today.