The climate for growing crops is getting better not only because of CO 2 increases, but also because of changes in temperature and precipitation. A slew of papers, some by Yr. It is these airmasses that, when they migrate southward over the United States, will kill your tomato plants if you put them out too early in the spring or don't protect them in the fall. If these air masses warm up a bit, the growing season lengthens. Furthermore, observations of precipitation and streamflow in the United States show there has been a general increase in moisture availability during the last century.
More moisture means better growing conditions.
Figure 1 Global temperatures vs. crop yields Figure 1. Global crop yields continue to rise, even as global temperatures heat up. The other USNA model, from the Canadian Climate Centre, is one of the most extreme. After all, it isn't really difficult to imagine that a longer growing season, combined with an increase in rainfall, makes plants grow better, and that the additional kick in the chloroplasts from carbon dioxide will send them into orbit. None of us wondered about that.