The problem with trees is they are used as lumber. The national parks has always been protected. But Trump has unprotected parts of the national parks to be cut down for lumber.

Can't they just put the algae in the ocean?

Back when I was a kid, trees still lived under water.

I guess it would take a lot of time to accommodate Mars for trees. More than for algae ;)

even your trees will be slop. nice.

Alternative in what sense?

The issue with trees is you need to adapt the city to them, you can't adapt them to the city. And people have proven once and again that they would invent anything to not move by an inch when our way of life is put in question.

So we push forward with absurd solutions one after the other: carbon capture, atmospheric geo-engineering, a damned nuke in antarctica, and now "liquid trees".

Because the alternative is to change our ways, and we can't face that.