When was the last time our scientists fully understood anything as broad as climate change or "OUR ONLY ecosystem"?

When mankind started to change the world through agriculture, deforestation and industrialisation, that's when we started to play russian roulette if you find that analogy useful.

We didn't know what it would do to our ecosystems but we did it because life back then was horrible and because we could. One bad crop and people were starting to die from starvation. Life is better now so we were right to take that risk.

It makes no sense to be alarmist about this basic disposition of mankind to take risks it doesn't fully understand.