Global warming affects crop yields, but it's the water not the heat

March 4, 2013, University of Queensland

( —The effect that global warming will have on plants is now better understood thanks to advanced modelling provided by The University of Queensland's (UQ) Professor Graeme Hammer, one of Australia's leading crop scientists.

For more than a decade, the professor in at UQ's Queensland Alliance for Agriculture and (QAAFI) has been developing increasingly to predict the growth and yield of .

In a paper published this week in Nature, Professor Hammer and his colleagues have demonstrated that the anticipated increase in temperature associated with global warming is not directly linked to an expected decline in yield.

Previously it has been accepted wisdom that the yield losses being experienced by maize growers during hot seasons in the American mid-west were attributable to temperature increases.

The modelling study has shown that it is the associated increase in the evaporative demand for water – causing increased plant – that will ultimately cause the decline in crop yield.

It is not a direct effect of on plant organs from the increase in temperature.

"These two factors are often related, but until now we were simply attributing projected yield declines to increases in temperature and heat stress – and it's more complex than that," Professor Hammer said.

"Our computer models are able to separate the mechanisms and explain what is actually going on.

"Increasing temperatures mean increasing demand for water and so greater plant water use and ultimately more during the crop life cycle.

"A good human analogy would be to imagine someone standing in a desert.

"You would start to sweat more as the temperature increased and more rapidly use up your reserves of water.

"It's a relatively simple concept, but one that has been overlooked until now."

Being able to accurately predict declines in the maize harvest and explain their physiological basis is a reassuring validation of Professor Hammer's crop models.

Historical data used in the study was drawn from locations across the American mid-west spanning nearly 50 years.

Explore further: Study finds growing evidence of global warming threat to future food supplies

More information: A preview of the Nature paper, The critical role of extreme heat for maize production in the United States, is available online at

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2.9 / 5 (7) Mar 04, 2013
Probably never be done, because there's always some excuse for some corporation to do what benefits them most in the short term (5 to 10 years) rather than what benefits them and everyone else in the long term, but NASA already has the solution to this. It's aeroponically grown corn, of which they can get an extra growing cycle, and ultimately raise far more corn per unit water. It's like double or triple the yield per unit water.

Problem is it takes a lot of aeroponics facilities to grow as much corn as the U.S. currently produces. Granted you wouldn't need them everywhere right away, only in the most heavily effected areas, but still...

Unfortunately, it's currently much CHEAPER in dollars anyway, to just cut down more forests or grassland and turn it into farm land.
1.4 / 5 (11) Mar 04, 2013
What *decline* in crop yield in an era of high CO2 increases in yields? CO2 fertilization means plants need less moisture.

"Our computer models are able to separate the mechanisms and explain what is actually going on." much for empiricism as the basis for science.

1.4 / 5 (11) Mar 04, 2013
" much for empiricism as the basis for science."

Couldn't have said it better myself.
3.3 / 5 (7) Mar 04, 2013 much for empiricism as the basis for science.

You could do a multi-controlled experiment.

Three greenhouses plus an open field farm.

Open farm simply grows the corn as any farmer would, serving as a first control.

Greenhouse A replicates presumed ideal conditions, serving as a second control.

Greenhouse B uses the same amount of water as A, but with a very high temperature cycle simulating AGW in 2100.

Greenhouse C uses same temperature as B, but uses extra water to adjust for extra evaporation.

If the conclusions of the modeling are true, we would expect B to be the worst performing.
3.9 / 5 (7) Mar 04, 2013
What *decline* in crop yield in an era of high CO2 increases in yields? CO2 fertilization means plants need less moisture.

No, it doesn't. Photosynthesis requires 2 moles of water for each mole of CO2. You can't make up for a lack of water by adding more CO2.

Now, greater irrigation and greater CO2 levels in the atmosphere *could* result in better yields, as long as we're careful about depleting the water tables.
1.4 / 5 (10) Mar 04, 2013
"thanks to advanced modelling"

I feel so much better now that the AGW research whores are using "advanced" computer models.
The Alchemist
1 / 5 (8) Mar 05, 2013
Nick, plants make sugars/starches from both H2O AND CO2. How did you miss that? (Cordially).

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