Climate impacts for 1.5°C are:
1) 1.5°C is more than ¾ of 2°C of warming (nonlinear, convex)
2) 1.5°C is ¾ of 2°C of warming (linear)
3) 1.5°C is less than ¾ of 2°C of warming (nonlinear, concave)
4) It varies by climate impact
5) Insufficient evidence (doesn't fit on Twitter poll)