Rise in CO 2 content is a tremendous benefit to global crop production .

A new paper prepared by CO2 Science's Craig Idso examines
Advancements in technology and scientific expertise that accompanied the Industrial Revolution initiated a great transformation within the global enterprise of agriculture. 
More efficient machinery and improved plant cultivars, for example, paved the way toward higher crop yields and increased global food production. And with the ever-burgeoning population of the planet, the increase in food production was a welcomed societal benefit. But what remained largely unknown to society at that time, was the birth of an ancillary aid to agriculture that would confer great benefits upon future inhabitants of the globe in the decades and centuries to come. The source of that aid: atmospheric carbon dioxide (CO2).   
The present study addresses this deficiency by providing a quantitative estimate of the direct monetary benefits conferred by atmospheric CO2 enrichment on both historic and future global crop production. The results indicate that the annual total monetary value of this benefit grew from about $20 billion in 1961 to over $160 billion by 2011, amounting to a total sum of $3.5 trillion over the 50-year period 1961-2011. Projecting the monetary value of this positive externality forward in time reveals it will likely bestow an additional $11.6 trillion on crop production between now and 2050.  

A great analysis worth reading here (pdf)