Agriculture is affected by global warming at least as much as global warming is affected by agriculture. This exchange is just one of many that point out the important reality that every action has a reaction. Many have argued that the indisputable fact of a warming earth could have a positive affect on growing things. This is true, but it is also not the whole picture. Increased carbon dioxide would certainly enrich a plant's ability to acquire nutrients, fix nitrogen and more, but there are other considerations.
Yes, oranges may be able to grow further north, but where does that leave the orange industry in Florida? What does it mean to the infrastructure already in place to grow soy, wheat, corn, cotton and so on in the new “orange belt”? In places like Canada, where entire forests and their products depend upon seasons, will all industry thrive or seep away like maple syrup?
Whereas, it is certain that plants need CO2 to thrive, and that in some regions a growing season can be increased, there are also other effects of warmer temperatures that are just as certain. In some places, increased (rain)precipitation, which is documented over the last fifty years, will green up entire ecosystems, but the increased severity of storms, and wildfires, and respectively droughts, will impact the same areas. Severe storms, such as heavy, rather than dry snow, as what is now frequently experienced in the now warmer winters of the Pacific Northwest, and Rocky Mountains, tumbles trees across homes, power lines, fields, denuded forests, and later, eroded soils.
This means more damage to falling trees, weakened branches and seed heads of most plants. This occurs in plains as well, where less protected soils are more likely to dustbowl away. Then, there is the economic costs, such as what is being seen with Super (Franken-storm) Sandy and hurricane Katrina, and various droughts and fires in the west.
Warmer winters also move animal species northward as well, but where do the northern species go? Extinction, and therefore a cascading spiral of diminishing bio-diversity follows. All food crops depend upon specific organisms, both animal and vegetable to live.
Humans need plants to live, and animals do as well. Plants need CO2 to continue to produce oxygen, and absorb higher levels of greenhouse gasses. However, a real life experiment with ever increasing heat asks for many consequences already being seen such as eroded topsoil, deforestation, desertification, acidification and depletion of marine life.
These are just the knowns, the total cascading and inter-dependent dance of life will no doubt lead to far many unforeseen consequences. These may not be worth tampering with while hands are already full with economic and logistical needs of areas already hard hit by floods, famines, droughts, wildfires and much more to come.