Singer: 'I wondered, what is the significance of this 2⁰C number -- and I concluded that it is the "Goldilocks" choice. It turns out, 2⁰C is "just right" -- not too small, not too large. Consider for a moment what would have happened if they had given a number like 0.5⁰C. People would have shrugged their shoulders and said, "Oh, we've already passed that threshold, and nothing has happened. So why worry?'