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For starters global warming is a scientific claim, slavery was a state of law. A law can be overturned with another law and enforced by police. Global warming cannot be simply overturned by a law, dealing with its effects is itself a scientific debate. For instance, emmissions reductions versus geoengineering, or simply mitigation measures such as irrigation and seawalls.
So while the slavery debate was about up or down on a law? global warming is a scientific debate over various theories and approaches to solving complex systems.
And take a good note that your article sounds extremely shrill and desperate.