Question: If "ideal" plant growth occurs with 1500 ppm CO2 and temperatures of 80-85F, why should we worry about 400 ppm CO2 and an average Earth temperature of 59 F?

Maximizing Your Plant Growth With CO2

The ideal level of CO2 supplementation to maximize plant growth in a well maintained garden is generally 1500 ppm

In one final twist of irony, as you begin to increase carbon dioxide levels to maximize plant growth you will reach a point where temperature becomes the limiting factor. In order to benefit from the highest levels of CO2 supplementation (1500-2000 ppm), you actually need to run your garden area warmer than normal (80-85 degrees)

Al's Journal : July 2007

the average temperature on Earth is a pleasant 59 degrees