i think they have core samples of ice that go back over 400000 years now and can show that the added load of global warming ingredients is due to man..primarily burning fossil fuels ..they were able to measure loads during previous cycles back 400k years and the current one..if you get a chance to watch the hearings that were on last week try to watch them if you have time..this question was asked by mccain last week and that's what they all told him
...hey...people still believe the earth is flat or 5 sided and that the moon landings were a hoax....i can understand healthy skepticism but not denial....there are already several pacific island communities that have been evacuated
because the sea level has risen over their islands....warming is here now...and we are driving it ....literally....