It wasn't mankind, that's for sure.
The fact is that our "scientists" insist that the earth has gone through "natural cycles" of  warming and cooling trends over eons of time.
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The earth has been going through a "natural warming trend" ever since the Little Ice Age ended.
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And oddly enough, global temperatures during the decades around WW2 were actually cooler than the last part of the 1800s to early 1900s.....exactly the opposite we should expect if mankind and pollution "causes" global warming/climate change.  
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And another scientific fact: Global temperatures today are right on par with global temperatures that existed in the century BEFORE the Little Ice Age.
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Thus you have 2 questions to ask Al Gore:
(1) What caused temperatures to be as high BEFORE the Little Ice Age as they are today.....if mankind is the problem.
(2) What caused the Little Ice Age.....and is that on our horizon in another 100 or so years?