RISING levels of carbon dioxide in the atmosphere may have a silver lining: doubling the size of the sweet potato, the fifth most important food crop in the developing world.
Most studies of the effects of higher atmospheric CO2 on crops have shown rising yields of rice, wheat and soy. The hardy sweet potato is increasingly becoming a staple in Africa and Asia, producing "more edible energy per hectare per day than wheat, rice or cassava", according to research group the International Potato Center.
Hope Jahren at the University of Hawaii at Manao and colleagues grew the plants at four CO2 concentrations: the current level of 390 parts per million, as well as 760, 1140 and 1520 ppm. The Intergovernmental Panel on Climate Change predicts that atmospheric CO2 levels will be between 500 and 1000 ppm by the year 2100.
For the least extreme scenario at 760 ppm, the team found the tubers grew up to 96 per cent larger.
The team is now testing their nutrient content. "Are these sweet potatoes any more nutritious," asks team member Ben Czeck, "or do you have to eat twice as many to get the nutrients needed?" Crucially, previous studies revealed the protein content in wheat, rice, barley and potatoes dropped by 15 per cent when grown under CO2 levels double those of today.
Czeck will present the work in December at the American Geophysical Union meeting in San Francisco.
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What About Warming?
Thu Nov 22 10:48:01 GMT 2012 by Eric Kvaalen
They increased the CO2 level but they didn't increase the temperature. The higher the CO2 level, the higher the temperature will be, and according to a recent New Scientist article, the overall effect on wheat and soy is to decrease yields. See (long URL - click here) and http://www.nber.org/papers/w13799.pdf
As for nutritional content, surely the CO2 wouldn't have much effect on the number of calories per gram of sweet potato. Sweet potatoes are not usually considered a good source of protein.
What About Warming?
Thu Nov 22 14:27:07 GMT 2012 by Tom Andersen
Eric,
(Re: paper you quote).
Do you really believe that crop yields in the USA will drop by 31% (best case) to 79% (worst case) in the the next 87 years?
Its a funny paper in that they predict that corn yields will fall everywhere in the USA with increasing temperature, even in north Wisconsin for example.
I can't follow how they go from how much a crop grows in one day to expected overall yield.
What About Warming?
Thu Nov 22 19:56:32 GMT 2012 by Eric Kvaalen
The authors themselves admit that the true effect would not be as bad as what they say, because farmers can plant earlier in the year when it's cooler ("These rather dire predictions hold growing areas and planting dates fixed"). But they go on to say, "A sensitivity check shows that moving planting dates one month forward would mitigate damages somewhat but would still result in sizeable impacts."
They say early in the paper that maize grows best at 29°C, which is 84.2°F. It does get that hot in northern Wisconsin, and with global warming it could go higher, and thus decrease the yield.
Without actually reading the whole paper, I think they model the distribution of temperature (or "heat") and estimate the yield on the basis of that.
What About Warming?
Thu Nov 22 21:42:44 GMT 2012 by David R Allen
Cassava becomes toxic to humans as you increase C02. Cassava feeds a third of the worlds population.
Research results here.
http://www.abc.net.au/catalyst/stories/2891924.htm
What About Warming?
Fri Nov 23 02:38:57 GMT 2012 by Karl
"The higher the CO2 level, the higher the temperature will be..."
That's only true if you average the earth as a whole. You could grow the plants at a higher altitude or in a different season.
A small increase in altitude has a large effect on temperature but a small effect on the partial pressure of CO2.
What About Warming?
Fri Nov 23 05:29:08 GMT 2012 by Eric Kvaalen
That's true. But I think the goal of the research was probably to know what would happen to the crops of people living in a given place.
It's true that they could plant earlier in places where the sweet potatoes are grown presently during a summer season. But in the tropics there's not much difference between summer and winter and maybe the people grow sweet potatoes all year long already.
The paper I cited above says that even if US farmers plant earlier, there would be a sizable negative impact on yields of wheat, maize, and cotton if the temperature goes up.
What About Warming?
Sat Nov 24 06:23:30 GMT 2012 by CA
Sweet potatoes are the main staple in many poor countries despite their low protein content. If that content were to be further reduced, this would be a great hardship.
What About Warming?
Sat Nov 24 16:51:45 GMT 2012 by Eric Kvaalen
That's true.
Climate Change May Supersize Sweet Potatoes
Fri Nov 23 14:51:50 GMT 2012 by W G Treharne
http://www.newscientist.com/article/mg21628924.300-climate-change-may-supersize-sweet-potatoes.html
Not only should we think of stopping population growth, we ought to reduce the population as well.
Is the CO2 take-up any greater for sweet potatoes as the CO2 level rises?
Climate Change May Supersize Sweet Potatoes
Fri Nov 23 18:43:17 GMT 2012 by Eric Kvaalen
Obviously if they grow faster they're taking up CO2 faster.
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