The earth is 4.5 billion years old. Over those billions of years, the sun has gotten ~40% hotter, which counteracted the reduced atmospheric greenhouse effect.

The earth is 4.5 billion years old. Over those billions of years, the sun has gotten ~40% hotter, which counteracted the reduced atmospheric greenhouse effect. We can't directly compare our current climate to billions of years ago with just atmospheric conditions. Also, I notice you said "plants have thrived", and not "major staple crops have thrived". Toxic algae bloom has its own sort of natural beauty I guess, but rice and wheat are both temperate crops and won't be able to grow near the equator if it gets much hotter. Please note that while hotter temps would warm up croplands near the poles, heat is not light and the tropics are so valuable for farming because they receive more light, not because they're hotter.