Wheat Production Threatened by Warming

December 23, 2014


A popular myth propogated by climate deniers since the early 90s, is that, with global warming, we’ll see increased crop production.
The most recent research does not support this notion.  Crop yields are heading toward a heat-induced drop at the very time when population pressures will be increasing across the most vulnerable areas of the planet.


Global warming will cut average wheat yields by six percent for every degree Celsius (1.8 Fahrenheit) of temperature rise in a bigger-than-expected brake on food production in a hotter world, a study said on Monday.

The report, by a U.S.-led team of scientists, said a six percent drop would be 42 million tonnes of 701 million tonnes of wheat production worldwide in 2012, highlighting a need to breed more heat-tolerant crops.

In recent decades, wheat yields had declined in hotter sites such as in India, Africa, Brazil and Australia, more than offsetting yield gains in some cooler places including parts of the United States, Europe and China, the study showed.

At the peak of the 2012 drought in the upper midwest, I spoke to Agronomist Phil Robertson of Michigan State University, at MSU’s Ag research station, where the green, irrigated lawn in the background belied the brown and crunchy dry conditions elsewhere in the area. Dr. Robertson is an author of the US Global Change Research progam’s evaluation of climate impacts US Midwest. He gave a thoughtful and measured evaluation of what crop research is showing about yields in a warming world.


A fall of 6% in yield may not sound dramatic, but as the world’s population grows the pressure on staple crops will increase.

Food price riots have been seen in several developing countries following sudden rises of less than 10% in food prices in recent years, demonstrating the vulnerability of the poor to grain prices. The global population is currently over 7bn and is forecast to rise to at least 9bn, and potentially up to 12bn, by 2050, which will put more pressure on agricultural land and water sources.

The research also counters the optimistic projections of some climate change sceptics, who argue that more carbon dioxide in the atmosphere will increase plant growth, as they take up carbon from the air for photosynthesis. But that hypothesis has been widely questioned, as the boost to growing is likely to be outweighed by other effects, such as higher temperatures affecting germination and water availability.

The scientists behind Monday’s report, published as a letter in the peer-review journal Nature Climate Change, said: “Understanding how different climate factors interact and impact food production is essential when reaching decisions on how to adapt to the effects of climate change. Temperature changes alone are reported to have potentially large negative impacts on crop production, and hotspots — locations where plants suffer from high temperature stress — have been identified across the globe.”



9 Responses to “Wheat Production Threatened by Warming”

  1. neilrieck Says:

    I saw something similar to this in a lecture back in 2011. At that time, agriculturists published this rule of thumb: “For every degree of leaf temperature over 76 F degrees a C3 plant is at a loss of 10% of its photosynthetic ability.”

    Now you don’t need a green thumb to realize that you get 100% loss at 86 F when a C3 plant closes its stomata to limit water loss. I published some related stuff here:


    Note: C4 plants (like sugarcane, maize, sorghum, amaranth, etc.) close their stomata at higher temperatures while CAM plants (pineapple, cactus, etc.) only open their stomata at night (in effect, they take a deep breath then hold it all day). Both have lots of sugar but not much protein.

    • neilrieck Says:

      Correction: C3 and C4 have the same cutoff temperature of 86F it is just that C4 plants operate fairly consistently until they hit the limit. It is only CAM plants which can operate at higher temperatures.

      • uknowispeaksense Says:

        Many Arrhenius plots will produce these sorts of cut-offs and rates of change in many metabolic processes within plants as a reaction to temperature or light or humidity. Care should be taken generalising though as there are differences between species and even within species from different climatic zones. For example see Woledge and Dennis 1982


        That said, I still encounter idiots quoting controlled environment glasshouse trials as evidence that increased CO2 is good.

        • neilrieck Says:

          Thanks for this reference. I live in Canada where photosynthesis in nature stops during the winter due to freezing so assumed the process was irrelevant in most other northern countries. This article does reference ryegrass and clover (both not grain crops) which I thought were planted by farmers to allow fields to recover so I’m certain that you will agree with me when I say “these crops will not directly save humanity from starvation”

          Your comment on “glasshouse CO2 use” is right on the money. The very first step of photosynthesis involves the photolysis of water (retaining H while discarding O to the atmosphere) which means the whole process cannot go any faster than this stage no matter how much CO2 is available.

  2. dumboldguy Says:

    There is another facet of the problem that has strangely not received much attention, even though it has been known about for years. That is the “double whammy” of reduced nutritional value of food crops on top of reduced yields. The “enriched by CO2” faster growing plants also do not metabolize nitrogen and trace elements as well and do not contain as much protein. In parts of the world where people are living on the edge food-wise, this had led to the phenomenon called “hidden hunger”—-they may get more food, but it’s not meeting their nutritional needs.

    A ten-year-old article but a good summary of all that:


  3. j4zonian Says:

    Twice (implied) food demand increases were misattributed in the article. The increase in meat consumption, biofuel use and industrial stocks (corn, soy) are the main drivers of crop price increases and increasing economic demand for cropland. Land speculation and concentration in Africa and elsewhere by US, Chinese and other corporations also plays a part. In other words, the problem is rich people’s greed and extreme profligacy, and by greatly reducing US and developed world meat consumption and car driving we could feed billions more. Distributing land fairly, efficiently, and with global self-interest in mind as much as compassion could dramatically increase our chances of survival.

    • dumboldguy Says:

      Ho-hum. Came to this thread from the California-Batteries thread hoping to find a more cogent comment from JeffyZ, only to be disappointed once more. I will again remind all Crockers to google our boy and check out his CV and his participation on all those other “fora” he visits.

      You will find that JeffyZ says he “has a degree in environmental education”, which fact might explain why he seems to be more of a propagandist than a serious and well-informed commenter that understands the science, economics, and politics underlying his bald assertions.

      Implied? Misattributed? Meat consumption? Does JeffyZ not understand that the food riots of the Arab Spring grew out of not demand but shortages? That the conflict in Syria is a result of climate change induced drought?

      Jeffy baldly asserts: “In other words, the problem is rich people’s greed and extreme profligacy, and by greatly reducing US and developed world meat consumption and car driving we could feed billions more”.

      Really? How many “billions more”? And what’s the time frame for achieving this? And for how long can we feed them in view of the fact that human population is still growing at an unsustainable rate? Got some data?

      JeffyZ also asserts: “Distributing land fairly, efficiently, and with global self-interest in mind as much as compassion could dramatically increase our chances of survival”.

      Really? WHOSE chances of survival? Quantify “dramatically”. Define for us “fairness and efficiency” in the context of land reform. Tell us how those who own the land will be persuaded to give it up for the sake of “global self-interest”? Where does “compassion” fit in the present day model of run-amok capitalism?

      Sorry, Jeffy, but spouting strongly stated but weakly supported opinions as an “environmental educator” is simply the spreading of BS and propaganda, and that can get you banned from many sites. For instance:


      Sally on February 3, 2009 at 12:58 pm.
      “…..so glad you gave “J4zonian” the boot!”

      Dennis M on February 3rd, 2009 at 1:31 pm. (owner if the blog)
      “As for J4zonian, he tried another comment today after I deleted several of his yesterday. He even asked why I’d not published his earlier propaganda pieces. If he asks that then he really has lost the plot!”

      Enough for now on this thread. JeffyZ also made two lengthy comments on the dying “Glum and Glummer” thread that need to be answered. One in particular is a classic illustration of the narcissist’s response to anyone who dares to question them.

      I will, however, share some tidbits from the “JeffyZ Files” before going.

      One is JeffyZ’s “solution” contribution to a thread on a blog—-“Solar railroads with connecting bike paths”

      Another is a closing from a long rant in which JeffyZ is apparently doing quite a bit of projecting—–“I weep and howl with the monstrous pathetic tragedy of Sphinctorectus oralis, the “civilized” human”, he says. He needs to look in a mirror.

      Earlier in that comment we also find—–“This argument has been going on for years, and so you’re being hit with the fallout of my frustration with others who have made the same debunked arguments, over and over and over and over and over and over and over and over and over. And over. And over”.

      (That’s ELEVEN “overs”) Hmmmmmm?

  4. Gingerbaker Says:

    Who needs wheat? Let them eat cake.

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