Guest Post by Willis Eschenbach
I keep reading these claims that we’re all going to starve because of global warming. People say it’s going to be the death of agriculture, that increasing temperatures will cause significant drops in crop yields. Here’s a typical bit of alarmism (emphasis mine):
A study by the International Food Policy Research Institute (IFPRI), indicates that climate change would hit developing countries the hardest, leading to massive decline in crop yields and production.
Whoa, a massive decline in crop yields due to increasing temperatures, sounds scary. So I thought I’d review the facts. Here is the global situation, showing the global yields of rice, corn, and wheat, along with the change in global temperature.
Figure 1. Changes in global grain yields and global temperatures 1961-2011. Data Sources: FAO, BEST, Photo
Now call me crazy, but what I see going on there is not a global crisis. Nor is it “massive declines”. Notice that (according to BEST) the global temperature has gone up one full degree centigrade … anyone remember any thermal crises that have resulted from that one degree of warming? Since two degrees is supposed to bring untold sorrows, where are the sorrows of one degree? Where is the lethal sea level rise? Where are the disasters? ¿Où sont les neiges d’antan? And most of all, where are the decreases in yield from that one degree of warming?
Of course, you could say that this is just because it’s a global average, and not all countries produce wheat, so we wouldn’t expect good agreement between global temperature and global grain production. And you might be right. So … here’s the same chart, only this time just for the US;
Figure 2. As in FIgure 1, except for the US rather than for the whole globe. BEST US temperature data.
Again, there is no thermal related decline in yields. According to BEST the US, like the globe, has gone up about a degree since 1960 … where are the climate refugees? Where are the corpses? Where are the thermal catastrophes? And more to the current point, where are the declines in food production? I don’t see them.
Finally, I thought “Well, maybe if I detrend all of the US data and then see how well related the change in annual temperature is to the change in annual crop yields” … no joy there either. Below are the measurements for those relationships. The strength of a relationship between two variables is measured by something called “R squared” (written “R2“), which varies from 0.0 for no relationship between the variables, up to 1.0 for perfectly related variables. Here’s the relationship of US temperature and US crop yields:
R2, US BEST Land Temperature and US Maize (corn) yield : 0.001
R2, US BEST Land Temperature and US Rice yield : 0.000
R2, US BEST Land Temperature and US Wheat yield : 0.022
In other words, no relationship at all. I gotta confess, I don’t see what folks are screaming about. If you believe the BEST data, we’ve seen a full degree of temperature rise in the last half century, and it hasn’t done us any harm—no atolls gone underwater, no millions of climate refugees, no increases in extreme weather. And through all of that temperature rise, the crop yields have kept going up. Will they reach a maximum? Assuredly they will … but it doesn’t seem like that maximum yield is going to be much affected by the temperature.
So I fear that once again we’ll have to postpone Paul Ehrlich’s celebration. He’s been predicting the global Malthusian food crisis for decades now, to no avail. Near as I can tell, according to the Malthusian philosophers like Ehrlich, the problem is that this continued increase in crop yields works in practice, but it doesn’t work in theory …
w.
Further Reading: I put up a post a while ago called “Border Transgressions“, about wheat production and temperature in Mexico. I also discussed how much food people actually have to eat in “I am so tired of Malthus“.
[UPDATE] Some people seem to have understood me as saying that because temperatures were rising and crop yields were rising as well, that the rising temperatures were causing the rising yields. I am not saying that. It may indeed be true that in a warmer world, the general yield would be better, and I see no reason it would not be better … but that’s not what I’m saying.
Some people seem to have understood me as saying that crops are not affected by temperatures above their optimum range. I am not saying that. All crops have preferred temperatures, above or below which they do not produce as well.
People are over-thinking this. What I am saying is simple. It is the answer to the question in the subject of the post—do increasing temperatures lower crop yields? I say no.
Note that I am not saying that increasing temperatures increase crop yields, although they may do so. Instead, I am falsifying the alarmists forecasting things like “massive drops” in crop yields. I’m not saying yields will or won’t go up if it gets warmer … I’m saying they won’t go down.
Here’s what lowers crop yields. Bad weather forecasts lower crop yields. If the farmer knows it will be colder next year, don’t worry, she’ll make money, she’ll plant later, use a different variety, plant beans instead of corn, get a bumper crop, be the envy of her neighbors. Same thing in reverse if she knows it will be hotter, she’ll plant early and have her crop in while the neighbors’ crops are wilting in the field.
But a bad forecast, she puts in hot weather seed and it turns out to be a cold year, the yield will go down.
So increasing temperatures, particularly predicted increasing temperatures, particularly predicted gradual increases over a century, will be lost in the noise of the thousands of changes that farmers do each and every year to account for the much larger interannual variations and interdecadal variations. Every year, the farmers successfully deal with the fact that not next century but next year may be two or three degrees warmer or cooler than this year … do you really think a degree’s rise spread over decades will affect those farmers’ crops? It’s lost in the noise, they’ve got three degrees to think about. Here’s the part that I think many folks don’t understand.
At the end of the day, crop yield is a measure of the farmers, not of the temperature.
In evidence of this, I offer the fact that the above analysis of the detrended US temperature data and detrended US crop yield data showed only an insignificant relationship between the two.
w.
[UPDATE 2] Someone downthread asked about the yields in the poorest countries. Here is that data.
As you can see, progress has been much slower in the developing world. However, even in the worst off countries on the planet, even with the warming of the last 50 years, the yields are still rising. And it is worth noting that the worst countries are all at or above the global average yield rates in 1961. In my lifetime, the poor of the world have moved to where the global average was when I was a kid …
And obviously, of course, at this end of the spectrum even the simplest of improved methods and seeds would double the yield … which is why temperature is not the issue, and never was.
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P.P.S: Anyone can see that the tropics are all desert. Vegetation cannot exist in a warm, humid environment. Show me the peer-reviewed evidence that suggests otherwise! You can’t be bothered to find it? Then I’ve won the argument. You didn’t respond? Then I’ve won the argument. You did respond with the peer-reviewed evidence that suggests otherwise? Then I’ve won the argument. Why? Because of peer review, arctic ice, the radiative properties of CO2, and Ultra Thundercane Sandy. That’s all I ever need to say.
What’s that officer!? I was speeding!? Perhaps you can point to where in the peer-reviewed literature it says I was speeding!? I wasn’t speeding, so just tear that ticket up. I can prove I wasn’t speeding because of peer review, arctic ice…well, you get the point.
–
markx says:
January 31, 2013 at 4:47 am
“Hang on, do you hold the position that storm was purely the result of climate change?”
–
Of course. Track with abrubt left turn by way of highly anomolous blocking high during and because of the Arctic sea ice minimum.
Tremendous intensification into the most energetic system the planet ever saw to measure, by crossing the axis of a record warm Gulf Stream.
It’s not hard to understand, but then I have something that is even easier to see: one swallow does not make summer, so a trillion swallows must mean Ice Age 🙂 Same logic gives Queensland, AUS, a flood of the century every year.
So well, Sandy just rinsed four thousand billion $ into the Atlantic. If you just kept up your dykes according to sea level rise for a tiny fraction of that cost, you know, you could still afford the luxury of climate revisionism. Now you guys are not just on borrowed money, you are operating on ruins.
As for the droughts hitting crops all over the world, biofuels won’t grow in droughts, like corn won’t. So maybe you really should start investing in biofuels 😉
/cRR
Most farmers are smart enough to grow crops suited to the prevailing conditions. As climate changes, in whichever direction, they will make the choices which make them the best returns.
I appreciated Mr. Hawkins’ adhockery, but the Procrustean narrative fallacy holds on public forums as well as in academia. Make your case and reserve argument (means defense) for peers’ reviewed literature (read the final clause closely).
“No adhockery. Bruno de Finetti coined the term “adhockery” to describe the profusion of frequentist methods.(http://www.johndcook.com/blog/2009/04/07/four-pillars-of-bayesian-statistics/)”
John Russell
seasonal weather variability would affect crops, normally causing a reduction in yields if the crops are already adapted to the historical average climate of the area and the year is beyond the ordinary range of fluctuation. Thus, if in a certain year you have extreme heat or a drought, the yields will be lower. In other years, with better weather, you’d get a bumper crop.
But this is not an effect of ‘climate change’. Climate change is a gradual change in the average climatic conditions, occurring over a number of decades and several generations. This involves also a gradual adjustment of plants, animals and farmers to the new conditions. Just as farmers in the past have adopted the most suitable crops, varieties, cultivars (or livestock breeds) and farming techniques for their particular farms, so would do their children and grandchildren (or the buyers of their farms if they decide to sell at some point) as the climate gradually changes amidst the endless year-yo-year weather fluctuations.
The main point here, I think, is to reckon that (as regards impact of climate change) agriculture is itself an adaptive activity of humans, not a natural system (as are, for instance, rainforests or ice caps). One cannot define or analyze future agriculture based only on the physiological response of plants: one should necessarily include the spontaneous response of farmers, and the exogenous progress and diffusion or agricultural technology. And one should also distinguish between a sudden jump in temperature or rainfall, either occurring in reality or simulated into a model, and a gradual change of average climate over 50-100 years.
Apols to Ed Hawkins for getting his affiliation wrong. I thought he was Reading Uni and MET Office.I know they work closely together anyway.
cRR Kampen says:
January 31, 2013 at 3:57 am
“O and climate change just dropped your economy into contraction…”
You are partially correct – O (aka Obama) DID cause our economy to contract (big time). Climate change…not so much. 🙂
Graham W says:
January 31, 2013 at 5:21 am
“P.S: Ultra-thunder-mega-super-hurricane Sandy!”
Remember those halcyon days back in the 60s when the climate was “normal” and our climate science geniuses were “turning on, tuning in and dropping out” at their liberal colleges? They NEVER had any bad storms back then, NEVER…
http://en.wikipedia.org/wiki/Hurricane_Camille
Willis,
This is the very first time I think you have overlooked something significant in your audits. In keeping with your excellent track record we must be careful to remain true to accuracy or else we risk opening ourselves up to questions of integrity. I’m not going to make a counter claim here but I would ask you to consider that U.S. agriculture is “Industrial Agriculture” which has benefited the most in the time frame you represented from advances in sustainable agriculture. On the flip side developing nations are primarily “Traditional Agriculture” which is well behind countries like the U.S. in areas such as soil conservation, pest control, etc. In short, our production has increased through knowledge and technology at a rate that climate variabilty either way cannot keep up with. It is true that climate warming or cooling could potentially and negatively affect crop yields worldwide. This would be more visible in developing countries. Still, the claims you respond to are alarmist in nature because temperature variability is only one aspect of cause. Shifting rain and wind patterns are due to ocean heat content (solar activity) are more likely to affect crop yields as they might limit irrigation and thus accelerate soil errosion issues in some areas while offering a net gain to others.
To Ed Hawkins:
Thanks for coming to defend your paper. One of your points have been raised by
others, e.g., there are temperature thresholds beyond which crops begin suffering.
Beyond that, you mention that 2003 was the hottest year in France and maize yields
went down by circa 20%. What was the rain situation that year?
Again, thank you for coming.
Did the study perhaps use Zimbabwe as the agricultural proxy for the rest of the world? Boy have they been hit hard by climate change (/sarc).
So much garbage in those claims; it’s hard to know where to start.
In addition to many available adaptive strategies (develop/use better adapted graine varieties), keep in mind that yield in the field does not feed people in the cities; bulk transportation infrastructure is required. Crop disruption due to floods, draughts, storms., etc. are regional events. In pre-industrial times they would also be regional disasters. Now we can transport sufficient food from unaffected areas to make up the regional shortfall. That is of course assuming we can continue to burn fuel to power the trucks, trains and ships.
To Chris R:
Good question – 2003 had lower than average rainfall, but not extremely low – 1962, 1964, 1986 & 2005 were all lower in rainfall for the maize growing regions. See Figure 2 in the PDF I linked to. Also, as irrigation has increased since the 1960s the sensitivity of yields to rainfall has reduced (Figure 4). In summary, both temperature and precipitation are important, but for 2003 it was predominantly the heat.
Ed.
Ed Hawkins says:
January 31, 2013 at 4:58 am
5) Our projection of a 0-12% drop in maize yields by 2016-2035 assuming no technology development is not exactly alarmist!
Props to Ed for commenting here at WUWT.
In the Guardian article linked on my blog, Ed says this:
“Our research rings alarm bells for future food security”
And his co-author Andy Challinor says this:
Supplies of the major food crops could be at risk unless we plan for future climates.
So if the paper only worries to a 0-12% extent, why make statements like these through major newspapers and scare the public?
1) For those in doubt about whether hot daily maximum temperatures reduce yields, then have a look at 2003 in Europe. The hottest (and presumably sunniest) summer ever in France, and maize yields went down 20% on the year before
Wrong on most counts. 2003 was no the hottest ever ever ever in france but it was very dry as most years have been since 2002. Watering of crops was banned in many important areas because rivers ran dry. Rivers like the Charente, Dordogne, l’isle etc. You need to do more research on science instead of funding.
My crops here have been very good not because it’s been cold but because it has been hot and I have been able to irrigate.
So gardeners and veg producers have been wasting their time and money all these years building green houses. Someone should tell them the new science “consensus” has dispelled this centuries old myth.
ROM has hit the nail on the head for a vast array of modern problems
“much greater danger from whack job city politicians and bureaucrats”
An interesting counterpoint to Ed Hawkins paper:
The paper states that maize has a temperature threshold point at 32 degrees C.
Above that threshold, yields drop. This is from the abstract:
“A significant reduction in maize yield is found for each
day with a maximum temperature above 32◦C, in broad agreement with previous estimates.”
Hmmm. That would be news in Hallam County, Texas. The daily high goes above
that threshold on 23 June and stays there for 52 days, on average. This is a very
far cry from the ~22 days above that critical temperature in France in 2003. Yet,
Hallam County’s corn harvest exceeded 20 million bushels in 2010 and yields this
year are still between 180-200 bushels per acre! The key is that Hallam County
corn growers, like all of the Texan panhandle corn growers, use irrigation.
Hawkins et al. attempt to correct for precipitation, and he correctly notes
that precipitation is negatively correlated with hot weather. I have not read his paper
in full detail, but it looks like an impressive piece of work.
I would say, to the title, it depends. Obviously higher temperatures will have different effects in different areas of the globe. Of course there is no such thing as a global mean temperature so a raise in one hemisphere could just as easily be a drop in an area of another. If higher temperatures lead to greater drought conditions on certain areas where irrigation is difficult then crop yields may indeed drop. However it could be just the opposite in areas where the temperature rises and annual rainfall rises with it, which seems to be the current conditions appearing in temperate climates ( here in the UK, despite the claims of record temperatures the annual rainfall is rising ).
The fact is that plants, on the whole, love warmer climes with wetter summers and higher available CO2. And given that’s what the alarmists are telling us is happening ( unless there is a convenient drought bandwagon for them to jump their hypocrisy to ) then I think crop yields, in general are in for favourable times.
Physiologically, crops are sensitive to temperature usually only during germination and flowering. A cold (or warm) spell at the wrong time can massively affect yield – 100% if you have, say, a frost during flowering in wheat and pretty high reduction for high temperatures during flowering in lupins (two crops which which I am familiar). Lack of moisture is also important, but here it is very difficult to separate overall rainfall vs a dry period in an otherwise wet year, which brings me to my main point regarding the study referred to by Tallbloke.
My first take on the french study is that the authors picked maize – a crop which is unusually sensitive to relatively short periods without adequate moisture. [In the US, the research into “drought tolerant” maize is focussed on withstanding a 4-week period without rain – not what you would call a drought for most people, but critical to maize yields.] I would like to know if the authors (I see Ed Hawkins has commented here) had considered rainfall as opposed to temperature in their paper, as well as periods between rainfall events. I would also like to see wheat yields for the year in question to see whether the high temperature affected a crop which is far less affected by dry periods (a far deeper root system).
As a researcher in plant genetics, I know that breeders can pretty much give you anything you ask for in terms of adaptation to growing temperatures. Temperate climates have massive within season temperature changes, far in excess of any postulated climate change, and there is no inherent reason why crop varieties cannot be bred to handle these small changes in average temperatures. If the outcome of the CAGW scare is to increase funding to crop breeding to increase the capacity to adapt to changes in the climate (in whatever direction), then this would be a benign, even beneficial, outcome. However, articles claiming the end of the world is nigh merely play into the hands of those who would hinder our capacity to adapt by forcing massive reductions in energy use to no useful purpose.
At the equator the world is covered in jungles. Plants like it warm. Thus we build greenhouses to grow them, and add CO2 to the greenhouses.
Why would plants object to turning the earth into a greenhouse?
And as a jab at those alarmists who enjoy talk of tipping points, if the Earth continues to warm as predicted by their silliness, there is a truly wonderful agricultural “tipping point.” That is, when farmers can begin to plant multiple crops on the same land, because the expanded growing season.
Don’t get me wrong. I don’t believe for a second that we’ll warm enough to have multiple planting seasons in most locations where only 1 planting season currently exists. I only mention this to note that not all tipping points are bad ones, and not all temperature increases, even massive ones, can be judged as all bad.
To Ed Hawkins:
Thanks for your gracious response. I see you state that irrigation has increased in
France.
I just posted, before I saw your response, a note about corn production in Hallam
County, Texas, where the high temperatures exceed your stated threshold for a very
long time, yet yields are quite high, due to irrigation.
Perhaps the corn (maize) cultivars used in France might be a little different from those
used in extremely hot Texas? Or perhaps increased irrigation could offset the heat
somewhat? That could obviate the concern you and your co-authors stated in section 4:
“Improved technology will need to increase base level yields by 12%
above current levels to be confident about maintaining current maize yields. The current
rate of yield increase due to technology is not sufficient to meet this target.”
Again, thanks for coming here to defend and discuss your paper, and I re-iterate my
appreciation for an impressive piece of work
Willis!
I made some calculations on world production of cereals (as production per hectar) in 1950-2010 and compared various parameters in relation to them. Actually I was interested in the difference in normal production and “organic” (“ecological” etc) production. For that purpose I tried to exclude the effect of some parameters to be able to extract the organic production. The increase in global production was more than twice in that period. The increase in cultivated area was about 10 %. So it was effectively about 100 % increase in the yield per hectar. Then I used data from Idsos on the effect of doubled CO2 levels on cereals (it was based on several hundred experimental studies). That gave about 7 % increase in the yield in 1950-2010 because of increased CO2. I never tried to estimate the effect of temperature because I thought it was too interconnected with humidity and varies a lot with latitude. I tried to estimate the relative importance of fertilizers, GMO and organic production. I could not do that because I simply did not find global statistics for organic production. I think most of the increase is actually attributed to fertilizers and partly to GMO combined with more efficient irrigation methods which prevent erosion. I estimated insecticides to have been a static parameter through times, that is they are continually developed in case of resistance.
Generally organic production gives something between 30-80 % of the normal production depending on latitude (it decreases towards high latitudes). I don’t know if there has been any progress in the yield.
I would really appreciate it if someone could clarify the following:
Is “CLIMATE CHANGE” intended to be a term describing
(1) a cause or:
(2) an effect
If it is meant to describe a CAUSE, then I would like to know
what it is that actually constitutes this ’cause’
and if it is an effect, then I would like to know what it is that is
the cause of this effect … and you are not allowed to cite
“global warming” !
Nice, Willis, but you left out the most important graph. What would the yield look like over time without global warming. For that you need imagination and a model, but it would be the only graph given credence by the nutters in charge.
Another chart, to be more serious for a moment, would be one that indicates demand for food grains. Regardless of weather (climate is stuck on 0) and increased yields, are we keeping up and warehousing the excess, keeping up and feeding the excess to our cars, or just staying even and starving the hungry while feeding our cars?