How overfed are we?

One of the possibilities for GW-damage is reductions in crop yield – up to 25%, in extreme scenarios. My reaction to that was “we all eat too much anyway” (well I certainly do) but some people did point out the obvious, that not everyone lives in the overfed West. Eli was kind enough to point to the FAO who tell me that in 2000 global average calories per day per person was 2807 (up from 24xx in 1970). The NHS tells me that the average adult should eat about 2,000 per day (women) and 2,500 per day (men) which we’ll average down to about 2,250 (m/f) and then down to 2000 (including children).

Which seems to count out to there being, globally, about 1/3 more food available than is needed (neglecting trivia like distribution and ability to pay). So there seems to be a fair amount of fat in the system (so to speak). And thats neglecting gains to be made from switching from inefficient meat-based nutrition to all going veggie.

[Update: Mind you, thisisn't good -W]


  1. #1 James Annan

    One of the possibilities for GW-damage is reductions in crop yield – up to 25%, in extreme scenarios.

    Note that these “extreme scenarios” are basically make-believe in which there are no (or at most negligible) technological improvements in the agricultural sector and even no adaptation to the climate change that is projected (and by “technological improvements” I do not even mean some hypothetical future pie-in-the-sky that may not come to pass, but merely the application of existing modern techniques in currently primitive areas).

    I recall previously offering to bet that agricultural production would continue to rise indefinitely and have not been overwhelmed with challengers…

  2. #2 Geoff

    A recent talk I went to in Cambridge suggested that we already grow enough food to feed double the current worlds population – if we went vegetarian!

  3. #3 Brian Schmidt

    I continue to think, admittedly with little evidence, that the biggest human impact (in terms of dead people) from AGW will be from reduced productivity for subsistence farmers, resulting in malnourished and dying infants and children. I don’t expect subsistence farmers will have the economic ability to use technological improvements.

    There’s very little new arable land that could be put into production, so their only cultural adaptation would be increased migration to cities, where they will encounter (and be part of) another set of economic and environmental problems.

  4. #4 Nexus 6

    The problem with your theory is that AGW is just one potential adverse impact on food supply. Add reduced arable land due to urbanisation, reduced soil fertility, reduced availability of fresh water (due to popn. increase), reduced availability of fertilizers, among other negative impacts. All this at a time when population is increasing, and the wealth of a large portion of that population (India and China) is rapidly increasing. Wealthy people want more protein in their diet.

    Additionally, investment in agricultural science is falling sharply world-wide.

    Effectively, we’ll need to grow twice as much food on half the land we use now, with far fewer inputs.

    Without a major change in the way we go about feeding ourselves, there will be massive food shortages for the world’s poorest people by mid-century.

    James, what are the terms of your bet?

  5. #5 Barry

    As the developing world gets richer meat makes up an increasingly large proportion of its diet, which as you point out is inefficient — at least in terms of land use.

    Most of the world’s soya production already goes to feeding livestock rather than people: if meat consumption continues to increase, the land available for crops intended for people will drop and the poorest will starve.

    I hope I’m wrong.

  6. #6 CW

    Neglecting “trivia” like distribution makes this a basically pointless observation. Actually, forget the “basically”.

    It seems that your definition of “we” differs from mine rather dramatically. Not even here in the “overfed West” is everyone getting enough food now, to say nothing about what a reduction in availability would do.

    [Really? Its a commonplace observation, which may not be entirely correct, that the poor are generally fatter than the rich around here. Certainly, any problems of hunger in individuals in this country are not due to lack of food overall, but due to distribution. Which rather reinforces my point -W]

  7. #7 speedwell

    Sure, we could feed everyone easily and more if we just all eat nothing but soy and wheat. Monsanto-proprietary soy and wheat, the whole world one big monoculture. Instead of looking forward to a nuclear war wiping us out, we could just look forward to some crop disease that–oops!–our GM crops would wind up being more susceptible to than non-GM crops.

    I’m a recently-diagnosed-diabetic vegetarian currently holding my blood sugar in check with a diet as low in carbs as I can get it. It’s monotonous and difficult. If I had to eat beans and rice every day, I would have to up my meds and go on insulin and probably die without sight or feet. But other people would get the food they need, that’s the point. Unless they are allergic to soy, or allergic to wheat, or have some other problem with simple basic foods. Tough on us, eh?

  8. #8 David B. Benson

    A recent FAO report also points out that about 20% of ‘agricultural land’ is currently unused; about 35% is ‘arable land’ in production. I don’t know what the remaining 50% is, forests and committed grasslands?

  9. #9 Eli Rabett

    Western agriculture is a procedure for turning oil into grain

  10. #10 James Annan


    I don’t think it ever got as far as a firm proposal, but something along the lines of: rising trend of gross production over the next 2-3 decades (analogous to the global warming bets) seems reasonable to me. This is so self-evidently inevitable that I find it hard to take seriously any research that asserts the contrary (and a careful reading of such research inevitably reveals that it is not actually a credible prediction, rather a sensitivity study that ignores both the strong background trend and the reasons for it).


  11. #11 llewelly

    Just an anecdote here – When I was in college, I took a nutrition class. I weighed in at 5’9” 130 pounds (1.75m 59kg) at the begining of the semseter, and at the end. During the semester we were required to track how many calories we consumed. I averaged 4500 calories a week. I’ve never been an amateur athelete of any sort. I consumed that many calories a week because I didn’t own a car, and yet I had a lot of places I needed to go.
    So I’m very skeptical that 2500 calories a day is adequate for farmers without modern technology.

    [4500 a week? 700 a day? Are you sure -W]

  12. #12 Magnus W

    Hmm sounds to me that you completely miss the point. If we today or yesterday or the decade before that and so on… used the best technique available there would be no troubles with food or water supply. However the poor countries can’t (money and knowledge) and some times don’t want to implement them ad to this global warming with changing with changing weather patterns (and increased population) and you get misery. Me thinks you are starting to sound a bit to much like Voltaire.

    [Mais non, zut alors, and stuff like that. James doesn't believe the predictions of decline, but I'll leave him to fight that out. What I'm saying is that even if you believe the predictions of decline, the real problem is not the effects of GW, its the problems of distribution, or inequity, or knowledge. Consider for example Zimbabwe: an obvious illustration of how badly you can do if mismanaged -W]

  13. #13 Magnus W

    And being my usual sloppy self… I did mean as I guess you guessed… living in the best of worlds and so on…

    I sure hope it won’t decline but that just is beside the point… relatively we are actually improving but still the absolute number of starving people in the world is increasing due to population increase. The way the world works IMHO global warming will significantly ad to the problems of starvation in the third world… However, there is no way in proving that with numbers and trying to do so just puts you in an endless debate about economics and politic ideologies. Global Warming is not the main reason but it will amplify the starvation and water problems around the globe… look e.g. in the Unesco world water report It’s not just me…

  14. #14 Gareth

    Well, I might just say WG2 and leave it at that…

    But, as someone who has a small farm, the one thing I worry about is drought, causing me to lose a year’s production, or floods. The two things I worry about are drought and floods, which erode my usable land and send it on a one way journey to the sea, and extreme heat. The three things… usw.

    Global averages hide a multitude of realities. I can afford to irrigate (at the moment I have money and water – in the future I may have neither). Others can’t. Consider the fate of Chinese, indian and SE Asian agriculture when the Himalayan glaciers are gone.

  15. #15 ice

    where does that global figure -25 % come from ? IPCC ?

    [No, nothing so authoritative. I think it might havebeen Eli. If anyone has a better, or a source, let me know -W]

  16. #16 Adam

    “[4500 a week? 700 a day? Are you sure -W]”

    He probably means 4500 a day.

    People doing heavy labour (including agriculture) will need (burn) over 3000 cal a day (male and female). Even moderate exercise (eg walking or cycling everywhere) requires higher levels than the NHS recommendation, which assumes a sedentary lifestyle. Similarly for cold climates, too.

    The WHO may be a better place to get a required average than the NHS. Just guessing though.

    [I think you must be right. Then a meaningful calculation would need to know how many people are doing heavy manual work. In the West, not many -W]

  17. #17 Adam

    “In the West, not many”

    No, hence the NHS assumption.

    There is a pdf on the WHO website (sorry no link, I looked at it over a year ago as part of a “what was I googling for” digression) that discusses research into how many people worldwide do what exercise. It’s looking into exercise for health improvements (other than against caloric intake), but it may give a good pointer to a rough percentage of people doing exercise. IIRC it discussed discretionary exercise (jogging, etc.), work-related exercise (labour) and transport related exercise (eg not driving).

    That’s not to say that’s the only place the data may exist, but if you do want to find it, it could be a start.

  18. #18 Nexus 6

    OK James, let’s look at where increased gross production can come from:
    1. Increase in area farmed – apart from the odd back yard, there isn’t any spare arable land. Most cities are situated in the centre of the best areas of arable land (alluvial soils and all that). As they expand, the most productive land is lost.
    2. Increase in yield via non-biotech methods. Let’s include more efficient use of arable land (i.e. larger farms like in Oz), plant breeding advances, better animal husbandry. Some advances can be made here. Unfortunately, all the low hanging fruit have been picked. The genetic background,or germplasm,available has already been reasonably well exploited. There will not be a second green revolution using conventional methods. Maybe an evolution.
    3. Increase in yield through biotech. The great unknown. Huge potential, yet to be realised.

    Will the increases outweigh the loss of land, fertility, water etc. + the expected increase in population and demand for protein.

    It’s an even money bet, at best.

    I’m a little pessimistic. I think the food production per head of population will almost certainly decrease over time. As for the gross production – depends on what happens in biotech over the next decade.

  19. #19 Dunc

    neglecting trivia like distribution and ability to pay

    Otherwise known as “the important stuff”. ;)

    There’s pretty much never been an actual shortage of food – famine is caused by a shortage of justice. Ireland during the Potato Famine, India under the Raj, Ethiopia in the 1980′s… All were major exporters of food.

    [Aha, you have cunningly fallen into my cunning trap. What you say is precisely my point. GW won't make us short of food. The problems will remain, as they are now, of distribution -W]

  20. #20 Magnus W

    [Aha, you have cunningly fallen into my cunning trap. What you say is precisely my point. GW won't make us short of food. The problems will remain, as they are now, of distribution -W]

    However, do you agree that GW is likely to increase the problems?

  21. #21 bob koepp

    “However, do you agree that GW is likely to increase the problems?”

    In my view, GW might increase the problems, but indirectly, via stupid reactions to GW by people (the real locus of problems). If we behave intelligently, on the other hand, we can increase agricultural production while reducing the percentage of the planet’s surface being destroyed in the name of food production.

  22. #22 Eli Rabett


  23. #23 Raymond Arritt

    There’s a lot of untapped potential even without further advances in technology.

    For example, maize yield under subsistence or small-scale agriculture in developing countries is of order 1 tonne per hectare.

    By comparison, yield for large commercial growers in Africa is around 6 tonnes per hectare and average yield in the U.S. state of Iowa is around 10 tonnes per hectare.

    Granted from a climatological perspective tropical locations are less suited for maize than the U.S. “corn belt” (e.g., our severe winters help by preventing diseases and pests from overwintering). But there would seem to be plenty of room for improvement through improved crop management in the developing world. The ag types around here say that many such improvements are not costly or technologically demanding; much can be done simply by advising local farmers on good practice.

  24. #24 guthrie

    The smallllll problem is raising yields substantially whilst we have less or more expensive gas with which to make fertiliser. Either way, food gets more expensive and poor people starve.

  25. #25 Andrew C

    Cary Fowler (one of the Svalbard seed bank people) gave a talk at my work a few months ago. He’s an agronomist, and I think it’s fair to say that he’s quite concerned about the prospects for global food production in a changed climate.

    If I can paraphrase what I understood his arguments to be:

    Development of new varieties of high-yield food crops takes of the order of decades. New varieties need to be produced continuously, as pests and diseases adapt. These high yield crops are highly adapted to local conditions – not just average temperatures and precip, but variability and photoperiod. For these reasons you can’t just take your seeds further north when you find that the local variability has changed so much that your yields have dived.

    He was particularly concerned about bananas, which a surprisingly (for me, not for them) vast number of people rely on as a staple, and for which there are only a handful of breeders.

    The takehome message seemed to be that it’s by no means certain that we will have reliable new varieties of food crops in time to maintain yields in changed regional climates.

    [Thanks for the comment. I largely agree. Re bananas, I understand they are a staple crop for a fair fraction of people. Fortunately, temperature change should be least around the tropics. The trouble is making something usable out of "it is by no means certain". You can use it as "there is a danger of..." or use it as "but we'll probably be OK" -W]

  26. #26 llewelly

    I averaged 4500 calories a week. I’ve never been an amateur athelete of any sort. I consumed that many calories a week because I didn’t own a car, and yet I had a lot of places I needed to go.

    So I’m very skeptical that 2500 calories a day is adequate for farmers without modern technology.

    [4500 a week? 700 a day? Are you sure -W]

    My apologies. I meant 4500 a day.

  27. #27 James Annan

    Llewelly, 4500 calories is sufficient for a serious amount of manual labour, and far above the norm. But you are right that calorie requirements would be (were) a bit higher for a world of manual labourers.

    Raymond Arrit is right of course. What does that imply for the way in which Nexus has apparently been mislead about the nature of the food “crisis” and the “low-hanging fruit” of spreading basic agricultural competence, I ask semi-rhetorically…

    BTW I did work for 2 years at an agricultural research institute (primarily farm management), before shifting into climate science. There is no money in it in the UK for a number of reasons, none of which relate to yield limits (which are still being pushed higher and higher, ie we have not actually reached any identifiable limits). And we are close to the top of the heap as far as yield goes – around 8t/ha *average* for wheat, more in some areas.

    Bananas are a special case because they are effectively infertile clones. It is certainly an issue of some concern for them although the heralded death of the crop (which has been talked about for years now) seems to have been somewhat exaggerated. In fact I’m sure I read somewhere about some progress in defending against the virus that is threatening them…

    Peak oil/gas may be a threat but that is a separate issue from climate change. And a well-run traditional mixed farm can be pretty productive, although they are currently undercut by the arable empires with their cheap inputs…

  28. #28 Andrew C

    James, Raymond: I left Cary Fowler’s talk with a sense that there was a real risk that we may not be able to develop new varieties of crops in time to avert major food shortages, due mostly to the time required to get new varieties out of the lab and into fields. Do either of you think this risk is significant?

    Also viz ‘application of modern techniques in currently primitive areas’: are current increases in yields due largely to the penetration of modern methods into new areas, or increasing yields in areas where modern methods are already used? If they are due to the spread of modern methods then it seems reasonable to expect this trend to continue, and so a continued increase in yields.

  29. #29 James Annan

    I can only imagine that he’s bought into the apocalyptic “climate porn” that infests some quarters of the media (and even scientific research to a lesser extent). Decades is precisely what we do have in order to adjust to a ~1C change which is only comparable to (local) interannual variability anyway. Bear in mind that special interests will always want to hype up the importance of their work! Note I’m not arguing that absolutely nothing needs to be done, just that it *is* being done and I don’t see any particular cause for alarm.

    Also worth noting that political problems have a strong impact – yields in Zimbabwe have dropped precipitously and more generally war zones are always a disaster. That is, there are areas where we are even going backwards but nevertheless global output increases. As in many other fields, it is hard to see AGW assuming a dominant or even large role in future changes, although it may be detectable in some cases.

  30. #30 Dunc

    [Aha, you have cunningly fallen into my cunning trap. What you say is precisely my point. GW won't make us short of food. The problems will remain, as they are now, of distribution -W]

    Actually, I was just agreeing with you. A strange phenomenon on the blogs, I know. ;)

    [There had to be a first time. It was so unusual I didn't realise, sorry -W]

  31. #31 Magnus W

    Yes “political” problems are important very important and it’s reasonable to think that global warming will magnify this. E.g. look at Tigris/Eufrat who will build a dam first to secure water recourses and how will the neighbours respond? This is just one example… (Ob, Aral lake, the Nile, Mekong, Ganges, Senegal, lake chad, incomati, la pata… etc.) UNESCO say “recent estimates suggest that climate change will account for about 20 percent of the increase in global water scarcity”…

    Providing the calories per person per day needed for adequate nourishment requires an average of 1,000 cubic meters of water (around 2,800 calories). Irrigation accounts for around 70 percent of all water withdrawals and this number is increasing. In the developing countries the amount of freshwater that is used for agriculture already is at such a high percent that hard choices have to be made about where the water is of most use.

    Still there are improvements all the time, but global warming will make a already tough task tougher…

  32. #32 CW

    Aha, you have cunningly fallen into my cunning trap. What you say is precisely my point. GW won’t make us short of food. The problems will remain, as they are now, of distribution

    Oh please! Is this like the guns don’t kill people argument? A 25% reduction in food supply won’t kill anyone, the fact that nobody ships food to the people the reduction leaves starving is what will kill them. That’s like saying it wasn’t because of the fire that the houses burned down it was the poor response on the part of the fire department that did it. Regardless of any truthiness in your argument you can be sure that setting fire to 25% more houses is not going to improve the situation even if you, personally, happen to live right next door to a fire station.

  33. #33 Eli Rabett

    Raymond those high yields depend on a lot of artificial fertilizer, and with peak oil, that is going to get a lot more expensive

  34. #34 JCH

    I recently spent some time with a friend who ranches on land that his family purchased around 1890 in western Kansas. He was picking corn that day. When he was a boy he helped his father harvest the corn on the same field. His father ran the team of horses that pulled the wagon and he and his brothers and sisters picked the corn by hand and tossed it into the wagon. A good yield was 40 bushels an acre – some years better and some years worse.

    From memory – on the day I was there they were getting around 180 bushels per acre (his record on that field is 230) – same field. They are dry-land farmers-getting about 16 inches of precipitation on average per year. The reasons for the increased productivity center on improved seed, improved planting and tillage techniques (non-machinery), and fertilizers and pesticides.

    He agrees that giving up any of those factors will reduce yields, but not all will have to be given up. With climate change, it appears to me his field will be lost altogether, and I don’t really see any automatic way to replace it.

    [Why will cl ch automatically kill his field? -W]

  35. #35 BAllanJ

    Just because we could feed everybody by becoming vegetarians doesn’t mean we will. Come on. We could have stopped global warming by banning SUVs and commuting by bus. Did we? If we don’t have enough food for both the rich to be omnivores and the poor to get by, then the poor will starve.

  36. #36 JCH

    We have around 120 million cattle in the United States. If we didn’t eat them we would have around 500 million.:) We feed them corn to finish them because it speeds fattening, and that makes grass-fed noncompetitive. People have developed a taste for corn-fed beef.

    We could go back to exclusive grass feeding. It would take some acclimation. When I took my kids to Australia they refused to eat at McDonalds because they did not like grass-fed beef.

    You are not going to grow commercial tomatoes, or any other veggie, on the pastures where I grew up.

  37. #37 JCH

    WC – from the precipitation map I looked at in the IPCC report, it appears his land will eventually become desert. I’m unqualified to interpret that stuff, so I’m probably wrong. With an annual of 16 inches, it is not far from untenable farmland now – in amount or pattern.

    [I think people can be a little over-zealous in deciding that land will become desert. Ppn is harder than T to predict -W]

  38. #38 Eli Rabett

    If we didn’t eat cattle we would not have very many of them at all. Chickens are about the most successful fowl on earth.

  39. #39 Ian Forrester

    The IAASTD (International Assessment of Agricultural Knowledge, Science and Technology for Development) Report was released six months ago. The IAASTD is an international body which has been set up in a very similar manner to the IPCC. Their mandate is to look at the best methods to ensure that agricultural needs for the future are met.

    There are chapters on bio-energy, biotechnology, climate change, human health and a few other areas.

    The report was written by over 400 scientists active in the field (excuse the pun) and was signed by 60 countries. Only three countries in attendance refused to sign, Canada, the USA and Australia. All three have governments very strongly allied to the GMO industry.

    Calorie content is not the only parameter which should be used when discussing hunger and malnutrition. There are a number of other important classes of nutrients which are limiting in the third world (in fact because of the Western world’s excess production of starchy crops over the past few decades it has been convenient to ship them overseas as a “humanitarian” gesture).

    Most people are not significantly knowledgeable in nutrition so most accept this as the solution to third world famine. It is not.

    To test someone’s knowledge of nutrition ask them the following question:

    You have just been shipwrecked close to a tropical island. You are the only person to get out of the ship alive. You see a number of packing cases from the ship’s larder marked “cheese”, “corn”, “potatoes”, “steaks”, “oranges”. You can only manage to get one ashore, which one do you select to give yourself the best chance of survival until a passing ship comes by? (They are very large packing cases and should last a year or more).

    The Executive Summary of the Synthesis Report can be found at:

    [I'm afraid I found that document frustratingly silent on questions like: how much can food production be expected to change in future, with or without climate change? They identify risks and so on, which is trivial. Does the actual body of the report have anything more numeric to say?

    As to your packing cases... I would expect steaks and oranges to rot quickly; cheese and potatoes more slowly, so I guess I'd go for the corn -W]

  40. #40 JCH

    It’s a joke,Eli. In India they do not eat much beef, but they have, by some accounts, 4 times as many cattle as the United States does.