A Little More on Climate and the Food Supply
I start with the table from Lobell et. al. 2011 which I showed in my previous post:
The issue was the effect on food supply, so it matters how much of each crop is used for food.
Of the 440 million metric tons (MMT) of polished rice produced in the world in 2010 ( Table 1), 85% went into direct human food supply ( 5 ) . By contrast, 70% of wheat and only 15% of maize production was directly consumed by humans. (Major Cereal Grains Production and Use Around the World)
Production and yield are from Table 1 above. The bottom right cell shows a net increase in the amount of the four crops used as human food of about a million metric tons. For a more precise calculation I should have converted tons of each crop into calories. I am assuming that the ratio is not very different for the different crops, but readers are welcome to check that.
In the course of the same conversation, one of the participants insisted that all studies of the future effect of climate change on the food supply showed it to be negative. I don't generally like getting into the game of dueling citations, for reasons I will probably discuss in another post. But I was referred to the latest IPCC report so looked at it, and found a table, Figure 7.5 in Chapter 7, that showed the distribution of predictions of the effect of climate change on mean crop yield over the 21st century. For both temperate and tropical regions, the median prediction was for a negative effect but more than 25% of the studies predicted a positive effect. Looking at the estimates that included the effect of adaptation, farmers changing what they did in response to changing circumstances, the median prediction was for a reduction in yield of less than half a percent per decade.