[Suicide Junkie]

"deadly" conditions are just conditions with a negative % (or maybe just really low like 0% to 15%) So, ten CI 3s should be able to boost that up 30% to 'harsh' or so over a year.
Whatever you do, It'll take a long time. I suggest throwing up a single CI3, and shuttling colonists over. Or, alternatively, destroy the planet, and rebuild it. Asteroids might not keep track of conditions.

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As for the race:

I knew it was gonna hurt reproduction badly when I chose it. I wanted to make the game harder without resorting to big AI bonuses.

Now, my pop grows by 50M people per turn Empire-wide, and I have to shuttle them around, and back to my homeworld.