[Graham67]

More CO2 makes plants grow taller, but not with more grain. Being taller, grasses (like wheat) often snap and fall over, particularly in storms. Crop fail.

We are at the shallow end of the changes that are coming. An exponential increase in CO2, means an exponential increase in temperature, slowed down by ocean cooling. The current +1'C is almost beneficial, the predicted +3'C..+8'C in 2100 will be devastating. The rain-forests will go brown and fail before +4'c. But currently it all seems so lovely.

[barney54]

How did plants survive in the past when co2 levels were much higher than today?

[benaadams]

We've just passed 400 ppm, everything was pretty different when it was much higher https://e360.yale.edu/features/how-the-world-passed-a-carbon...

> To find a time when the planet’s air was consistently above 400 ppm you have to look much farther back to the warm part of the Miocene, some 16 million years ago, or the Early Oligocene, about 25 million years ago, when Earth was a very different place and its climate totally dissimilar from what we might expect today.

Towards the end Miocene was when grasses began to emerge significantly

> The higher organic content and water retention of the deeper and richer grassland soils, with long-term burial of carbon in sediments, produced a carbon and water vapor sink. This, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. C4 grasses, which are able to assimilate carbon dioxide and water more efficiently than C3 grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago.

https://en.wikipedia.org/wiki/Miocene#Flora

[salty_biscuits]

Really well (jurassic had co2 of thousands of ppm), but the current rate of increase of co2 is unprecedented. We are in uncharted waters...

[losteric]

Those were different plants, adapted for their times. Thousands of generations of natural evolution and human domestication led to the crops of today.