Currently atmospheric CO2 is at a level where almost all crops will start growing faster than weeds with anything above 400 PPM. At 800 PPM crops would grow much faster than they currently do. I think you would probably be able to discern a global warming signal out of the data. Interestingly enough, corn and weeds and many grasses, show very little enhanced growth beyond 400 PPM.

None It would likely eliminate all humans, most animals and much of the marine life, On a positive note, the planet would eventually heal itself

Plants would love it and be more productive. Just ask any greenhouse owner who has raise the level of CO2.

A lot of benefits, because Carbon Dioxide is a very beneficial thing. It is hella useful.

I would live closer to the ocean.

massive increases in biodiversity all over the planet.

C prove it. Show us the evidence that animal and marine life was eliminated because of CO2 back when it was over 1000+ parts per million.

I am looking forward to it, a beautiful green world with very few deserts, agriculture so improved that we will have enough to feed our populations without having to encroach on our natural environment.

You might think Dook and C are joking. It would be a logical conclusion but I don't think they are. Plants would be able to close off their openings called stomata that allow CO2 intake and therefore plants wouldn't need as much water. This would probably be beneficial to most plants IMO. I suspect the warming associated with the addtional CO2 would be moderate and if anything the additional green house gases would tend to moderate the lowest night temperature and winter temperatures.

Year round ship travel across the North Pole between the desertified hell-hole that was once China, and the shrunken and relocated ports of Europe.