Sunday, May 08, 2011

Climate change knocks wheat and corn production down 4-5%, US not hit so far

Interesting paper saying global production of wheat is down 5.5% from what it would've been without climate change (i.e., increased at a slower rate), and corn down 4%. Rice and soya unaffected.

Staple food tends to have inelastic demand, so a 5% drop added onto a shortage for stochastic reasons could have significant impacts on prices, with resulting social disruptions. Like Michael Tobis, I'm not sure why some people find this climate/food price issue to be such a strained argument.

I should note that the study gave an overall figure and not a specific for extreme conditions. Maybe climate change moderates the extreme conditions - or maybe not, and it makes extreme conditions worse so that the 4-5% figure is an underestimate in bad times. I'd guess the latter is more likely than the former, but we'll have to find out some other time.

The same study says North American hasn't been hit, yet. We'll have our turn at some point though.


  1. The latest IPCC projections I'm aware of were that the next 1-3 degrees of warming would on-net increase agricultural productivity. So for any crop you can find that's doing worse somewhere, you can probably find others that are doing better somewhere...and this should hold true for the next 50 years of warming. CO2 is plant food, and there are at least as many places that need more warmth to be maximally productive as there are that need less.

    This study didn't even say production was "down 4-5%" relative to any real-world benchmark - it rather said production was lower than some model predicted it *could* otherwise have been, while yields were still increasing.

  2. Got a cite for that, Glenn? I suspect the advantage is for increased CO2, not temps. And lots of weeds like the increased CO2.

    Agreed the decrease was relative to anticipated yields without climate change. No one disputes that yields are increasing from technology and breeding.

  3. No, I believe it's temperature more than CO2 that helps the food crops. Though they both do help. Sure, try this cite:

    Most reporters like to cherry-pick out only the scary negative speculations from pages like that, but if we instead consider the good parts, they include:

    "The preponderance of evidence from models suggests that moderate local increases in temperature (to 3ºC) can have small beneficial impacts on major rain-fed crops (maize, wheat, rice) and pastures in mid- to high-latitude regions [...] These results, on the whole, project the potential for global food production to increase with increases in local average temperature over a range of 1 to 3ºC, but above this range to decrease[...]Globally, commercial timber productivity rises modestly with climate change in the short and medium term, with large regional variability around the global trend (medium confidence)."

    Basically, the parts of the world that are *already* the best at producing food crops benefit from a longer growing season and being able to farm further north. There are also places where local warming would be expected to *reduce* existing crop productivity, but the increases in the places it gets better dwarf the losses where it gets worse, so the globe is better fed. (Also in tropical areas people probably would substitute into farming trees instead. Tree-farming *would*, as you say, benefit mostly from the extra CO2 and not be as much affected by the warming.)

  4. The problem with the headline "US not hit so far" is that the word "hit" implies it would be a bad thing. The same sources generally predict that if and when the US is measurably "hit" by climate change - when we have "our turn" - it will improve crop production. And is likely to do so for essentially the entire century. Which gives us quite a long time to wait for any downside to sow up. While waiting, our well-fed kids and grandkids and great-grandkids and great-great-grandkids seem likely to learn more science and invent/adopt more technology such that AGW seems as silly an old worry to them in the year 2100 as the problem of too much horse manure or not enough firewood seems to us now.

  5. I just found the quote I had been looking for specifically with respect to US crops being "hit". It is:

    "The IPCC concluded that, for North America as a whole [...] studies project likely climate-related yield increases of 5-20 percent over the first decades of the century, with the overall positive effects of climate persisting through much or all of the 21st century." (source)


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