Update:
Visual:
I tried to give the tree a more "tree-ish" appearance trough "connecting the stemm more to the ground (slightly wider bottom)" I added a 2-coloured version to even stregthen the "tree-ish" appearancewith through  a leaf-covered look.

Claim:
I decided to use the claim "180° for green enrgy" because it 1. perfectly discribes what Greenpeace aims at politically and 2. at the same time discribes in words what the logo does visually: by turning the power-button 180° it becomes a tree as symbol for green energy.

Alternatives:
I´ve also add some alternatives with other positioning of the claim, and the claim itself changed if it needs to exactly say "100% green energy for 2050"

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180 degree for green energy....

... this idea I was lead to when playing with the "power-button", a good symbol for energy consumption since it speaks for all kinds of energy.

Turning it 180 degree it gets the look of an tree. Quite a good symbol for green energy.

Additionaly it says exactly what we have to do in energy-policy: turning 180 degree to a sustainable way of energyproduction.