You cite a draft of the Sixth Climate Assessment Report (Chapter 5: Food, Fibre, and other Ecosystem Products). Indeed, that says the climate is stunting crop yields. I think that is false. Over the last 30 years we have seen massive increases in agricultural production and the greening of the earth in areas that had minimal vegetation. The climate assessment and the memo to President Carter run counter to the observed fact. By the way, the scary ABC graphic in your story shows emissions of water vapor, the primary greenhouse gas, not carbon dioxide, which is invisible.