As CO2 has risen, agricultural productivity has increased. Life thrived on Earth with CO2 at 10-20X current levels. The Arctic Ocean was ice-free 6,000 years ago when CO2 levels were only 280 ppm.
During the last glaciation, which peaked 18,000 years ago, CO2 bottomed out at 180 ppm, extremely likely the lowest level CO2 has been in the history of the Earth. This is only 30 ppm above the level that plants begin to die. Paleontological research has demonstrated that even at 180 ppm there was a severe restriction of growth as plants began to starve. With the onset of the warmer interglacial period CO2 rebounded to 280 ppm. But even today, with human emissions causing CO2 to reach 400 ppm plants are still restricted in their growth rate, which would be much higher if CO2 were at 1000-2000 ppm.
If humans had not begun to unlock some of the carbon stored as fossil fuels, all of which had been in the atmosphere as CO2 before sequestration by plants and animals, life on Earth would have soon been starved of this essential nutrient and would begin to die.