Illustrating global warming—What does "a 2°C increase" refer to?

Source: AMERICAblog (blog)
Details: The last few posts about global warming (the fast road to climate catastrophe) have referred to a 2°C (3.6°F) or 3°C (5.4°F) increase in global temperature as really really bad — not for the planet (she will do just fine), but for us. Those posts ...

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