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Maize harvest to shrink under Global Warming

Posted on 16 March 2011 by Rob Painting

With global food prices at an all-time high, out comes a new study demonstrating once again, that global warming will generally have a very negative impact on food production. The study shows that warming of 1°C will lead to smaller maize (corn) harvests throughout Africa.

David Lobell (Lobell 2011) and his co-authors analysed a dataset of over 20,000 maize crop trials which had been carried out in Africa between 1999 and 2007. These trials had originally been designed for the purpose of testing new varieties of maize, and were especially useful for climate research because the trial locations covered a broad range of environmental conditions dotted throughout the continent. By comparing the trial data with that obtained from local weather stations, the authors found a relationship between warming, rainfall and falling crop yields.

Surprisingly, for a crop previously thought to be tolerant of warming, the study revealed that maize yield fell in crops exposed to temperatures above 30°C. At sites in ideally managed rain-fed conditions, for every degree day (degree day = a tally of hours over 30°C adding up to a 24 hour period) over 30°C yields fell 1% And for plots in managed, but drought conditions, the yield fell further, a 1.7% decline for every degree day over 30°C.

Next the authors calculated the likely effects on crop yields if average growing season temperatures at each site, were raised an additional 1°C, as shown below:

Figure 1 - Model estimate of yield impact of 1 °C warming for trials at different average growing-season temperatures. Shaded areas show an estimate of the 95% confidence interval.

The last step in the study was to compare what effect an increase of 1°C might have on future maize cropping in Africa. They discovered some cooler regions benefit from the warming, but the majority fare poorly. Under ideally managed rain-fed sites, projections show yield declined in 65% of areas where maize is currently grown. Under drought conditions this decline impacts all areas, with 75% of areas seeing yields fall by over 20%.

Due to the large scale and geographical extent of the trials, the study analysis represents the best understanding, to date, of how maize/corn harvests will fare in a warmer world. Regions such as Central and South America, where maize is a diet staple, are also going to be badly affected by rising temperatures and falling yields.

That hammering sound you may hear is another nail being driven into the coffin of the argument It's not bad: it is that bad.

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Comments 51 to 56 out of 56:

  1. Rob Painting at 17:52 PM, re "All due to selective breeding?" For goodness sake, read the whole statement so you don't keep taking things out of context. If you were not up to imagining what "many factors" might include, I would have thought the very next sentence would have given some idea.
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  2. John D - "For goodness sake, read the whole statement so you don't keep taking things out of context." John, I don't see the point in comparing rich Australia with most of Africa which is poor. The higher yield of Australian crops are because of industrial farming practices, not primarily selective breeding, as in the case of the Lobell study. It's that apples and oranges thing (see I'm keeping the references agricultural). Probably a good thing in one respect, industrial farming practices aren't very good for the environment, particularly the aquatic one.
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  3. Rob Painting #48 "Charlie A - A 1C global warming is small compared to normal year to year variations and doesn't present a major challenge, on the average, to the crops in the areas that are currently optimal for that crop. Not what the study & particularly the rather obvious graph in the middle of the post reveal." If the graph in the middle of the post your refer to if Figure 1, then you are incorrect. The figure in the middle of the post is for all areas, not the areas currently under cultivation. The relevant figure has been posted in comment #25. And you also posted a couple of the relevant sub graphs in your comments. 1. Look at your comment #24. The 2nd graph. (D) current maize growing land (% of land area) chart. Please note the the heavy green area in South Africa, just north of Lesotho. 2. Now go to your comment #26 and look at those same areas. Note the blue, indicating INCREASED yield, not decreased? Look at other areas with a high percentage of maize growing. Then look at the modeled predictions for the effects of 1 C global warming. There is an interesting correlation that is highly unlikely to be random.
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  4. Charlie A at 23:32 PM, my first post on this thread began questioning whether the study told us anything not already known. It appears that the weak point in that statement centres on the word "us", so before the question was addressed I should have defined "us", however I think this thread has done that along the way. For myself, "us" means those people whose understanding is based on what is so readily evident and verifiable in the real natural world, the real physical world. For others, "us" means those to whom the same understanding only becomes real if it has been presented in a peer review study. It's not a matter of the first group ignoring that what the second group depends on, it's a matter of deciding what comes first, getting the job done with the paperwork to follow, or the other way around. This is often a point that defines the perspective of those who are in private enterprise and those who are not. In this particular case, if one wanted to understand how maize responds to changing temperatures, that question was being readily answered in the real world by observing where it is most prolific, and then observing how the growing of it diminishes as conditions change moving away from where they are optimum. If one wanted to know how a 1°C warming or drought conditions affected the crop, that evidence is provided by those who grow the crop under those conditions. If one wanted to know the limits to growing maize, then that will be found by observing where the cultivation ceases. Possibly one of the most authoritative sources as to what that limit is will be any peasant farmer who has avoiding perishing, perhaps merely (significantly?) by growing a different variety. Consider each peasant farmer a source of data. Collectively they yield the most meaningful data of all. It is therefore not dependent on conducting a study to identify those areas that are already beyond where maize is able to be cultivated to discover that if it warms even further that the yield of the non-existent maize will be even less. What would have been of value would be a study tracking the progress of the best of the new varieties being developed by measuring whether they are extending successful cultivation into those more marginal areas or if the pace of new development is failing and the marginal areas are advancing. Only with that knowledge would we be able to make projections into the future. There are two variables involved, the climate, and plant genetics. This study effectively froze plant genetics at a point more than a decade ago.
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  5. CharlieA @ 53- If the graph in the middle of the post your refer to if Figure 1, then you are incorrect. The figure in the middle of the post is for all areas, not the areas currently under cultivation. Both wrong and clearly doesn't make any sense. I think willful contrarianism is clouding your thinking. Read the study and the caption again. The graph, the one I placed in the middle of the post, is the average growing season temperature for the trials. The trials, quite obviously (but not to you) were carried out in areas already conducive to maize cultivation. Clear enough?. CharlieA -1. Look at your comment #24. The 2nd graph. (D) current maize growing land (% of land area) chart. Please note the the heavy green area in South Africa, just north of Lesotho. 2. Now go to your comment #26 and look at those same areas. Note the blue, indicating INCREASED yield, not decreased? Yes, as my comment at @26 points out, 65% of current maize growing areas decline under managed rain-fed conditions with 1°C of warming, not all areas. And your point is?.
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  6. With all the arguments there is one factor that seems to have been most carefully ignored, the one that has more impact than any other. Population 1960-2010-2050 projected. Southern Africa: 19 - 64 - 106 million Western Africa: 80 - 315 - 638 million There have been changes in the past and it is well possible that the same science and technology that has extended life and survival is now causing more changes but the biggest change of all is this vastly increased human burden.
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