I didn't know this. Do you have a source, or is this speculation only? In fact, the Googling I did, with several articles, seems to indicate this is not only wrong, it's heavily biased towards solar saving more CO2 output than trees offset.If you want to contain CO2, plant the same area in trees or other vegetation and you have reduced atmospheric CO2 more than by using solar power to generate electricity.
Example source: Tree Math 2: Solar vs. Trees, What’s the Carbon Trade-off? | The Energy Miser
Also note this is for New England, so areas where sunlight is stronger or less cloudy would see an even larger benefit.