CO2, photosynthesis, crop yields

Sadly, we may be finding far too soon.

Research seems to indicate that if the only change is CO2 then there will be an increase in crop yields. The problem is we don't know what other changes in climate will occur.
Too much rain will wash out many food crops.
Too little rain will eliminate any increase in yield from CO2 increase.

Then there are other issues.
http://news.nationalgeographic.com/news/2002/11/1122_021125_CropYields.html

Sadly, we may be finding OUT far too soon.

Re the history of CO2 levels: the (scientifically provable) fact remains that:"The present level is higher than at any time during the last 800 thousand years, and likely higher than in the past 20 million years."

Furthermore:

"This addition, about 3% of annual natural emissions as of 1997, is sufficient to exceed the balancing effect of sinks. As a result, carbon dioxide has gradually accumulated in the atmosphere, and as of 2009, its concentration is 39% above pre-industrial levels."

http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere

Here's yet another good info resource for projection of the effects of increases of CO2 on crop yields:

http://www.plantphysiol.org/content/early/2012/10/10/pp.112.208298.full.pdf

Nowhere online that I could find anything indicative of any data that discusses effects of increases of CO2 to levels of 1000 ppm.