Actually global warming is real. It started some 15,000 years ago, finished off the glaciers, and caused sea levels to rise an estimated 400-460 feet. Most of this was finished by about 5,000 years ago; sea levels have risen maybe 30 feet since that time.
That's where a lot of our prime 10,000 year old sites are, under water offshore where they are really hard to get at.
I'll bet that was when humankind started to use fire! See! Global warming is the fault of humans!