Thursday, August 16, 2012
After writing yesterday's post, I realized I was almost certainly thinking about the problem the wrong way. In particular, I implicitly set the problem up as question about whether the trend in yields might turn negative in the near future. But I realized that it would take an extremely severe scenario for that to occur - much worse than current science will support.
Let's take for example Dai's projections for the 2030s (based on analysis of the Palmer Drought Severity Index in climate models from the IPCC AR4). In that scenario, the maps looks like this:
They were certainly down, but they were 20-25% below normal, not 50-80% below normal.
Secondly, there will not be a drought every year from here on - even if we assume Dai's projections are right. Instead, in that scenario, there will be many relatively normal years in the next few decades, but the droughts will become gradually more severe and more frequent. In the normal years, yields will continue to increase as agricultural technology is likely to continue to improve (and in particular the biologists are likely to be very focussed on improving drought tolerance). We might expect the pace of increase to slow (as drought increasingly becomes normal) but it's very unlikely that yields in the more normal years will drop.
In short, we might expect the future projection to 2040 to look a bit like this:
This is a hand created scenario for corn yields that involves increasing variance and a slowing trend, but not an actual trend reversal. I think this is more what we might expect to see if Dai turns out to be right.
Of course, this is still not going to be fun - it would mean a lot more years like this one with big droughts and much higher food prices (particularly as population continues to grow against a slowing and choppier yield trend).
And by 2100, things could be seriously ugly.