Saturday, September 10, 2016

Future Climate and the Food Supply

I recently had an experience both rare and pleasant, a civil and informative argument about climate on FaceBook. It was started by
One of the commenters, although not prepared to defend the hysterical tone of the posted piece, was willing to argue that climate change was making the global food situation worse and threatened to make it much worse in the future. In defense of that claim, he cited "one recent study showing four major global crops declining (relative to no climate change)." The article, "Climate Trends and Global Crop Production Since 1980"  (Lobell et. al. 2011), was an attempt to separate out the effects on four major crops of different environmental changes–temperature, precipitation, and CO2 concentration–occurring from 1980 to 2008.

Reading it, I noticed that what the authors defined as the effect of climate change included temperature and precipitation but not CO2; its (positive) effect was listed separately. Including it changed the conclusion from four crops down to two down, two up. The commenter who offered the article as evidence had apparently missed that fact.

I also noticed that while they found a significant warming trend over the period, the trend in precipitation was statistically insignificant – consistent with random change. Redoing the calculation using only the two effects we knew were associated with AGW, warming and increased CO2 concentration, made the percentage increase in rice equal to the decrease in maize, the increase in soybeans larger than the decrease in wheat. The figures are shown in Table 1 from the article.

The table showed no effect of increased CO2 on the yield of Maize. Maize, as the gentleman I was arguing with pointed out, is a C4 crop, the other crops C3, the difference being in the details of the mechanism for photosynthesis. The effect of CO2 fertilization on C4 crops is substantially less than on C3 crops but not zero. Looking at another article that had been linked in the discussion, this one from the EPA, I found:
The yields for some crops, like wheat and soybeans, could increase by 30% or more under a doubling of CO2 concentrations. The yields for other crops, such as corn, exhibit a much smaller response (less than 10% increase).
That suggests that the effect is less than a third as large as the effect on the C3 crops but still substantial. Including it on Table 1 makes the negative net effect on maize smaller than the positive effect on rice.

Looking at the EPA article I noticed that the increase in  yield due to CO2 fertilization was presented as a fact, various things that might decrease yields as possibilities.
"if temperature exceeds a crop's optimal level or if sufficient water and nutrients are not available, yield increases may be reduced or reversed." 
"Extreme events, especially floods and droughts, can harm crops and reduce yields."
 No evidence was offered that any of those things would happen or how large the effects would be if they did. It looked as though the authors wanted to give the impression that climate change would reduce agricultural yields but prudently stopped short of saying so.

I also noticed:
"Overall, climate change could make it more difficult to grow crops, raise animals, and catch fish in the same ways and same places as we have done in the past."
As conditions change, people change what they do in response. If temperatures rise, farmers will shift to crop varieties suited to a warmer environment. If rainfall increases or decreases, they will adjust crop varieties, irrigation, other details accordingly. What would happen if farmers ignored environmental changes in deciding how to farm tells us very little about what will happen in the real world. Whether or not we have global warming, it is quite unlikely that, a century from now, people will grow crops, raise animals, and catch fish in the same ways and the same places as they do now.

The same issue is relevant to the other article. The authors estimated the effect of increased temperature on yield by looking at how yields had varied with temperature, year by year, in the past. Those estimates were  used to calculate the effect of the overall increase in temperature over the period and suggest possible effects of future increases.

To see the problem with that approach, consider a farmer at planting time. He does not know how hot the year will be, how much rainfall there will be. Decisions such as when to plant and what varieties to plant can only be based on the expected value of those variables.

A farmer in 2100 knows what changes in climate have occurred over the previous century so  can take account of those changes in how he farms. It follows that models based on observations of year to year variation will show a more negative effect of climate change than can be expected from gradual change over a long period of time. The authors of the article noted that problem along with other limitations to their analysis.

Most of the time, all I learn from arguing climate with people on FaceBook is how unreasonable most people engaged in the argument, on both sides, are. This was a pleasant change. 

I will have to wait to see whether my opponent has become less confident that climate change threatens the global food supply now that he knows that the article that he thought supported that claim is, if anything, mild evidence against it.


At 9:19 AM, September 10, 2016, Blogger Fred Mangels said...

I would think it unlikely your opponent, a Believer, will change his mind. You can no more convince a Believer that man isn't responsible for climate change than convince a Christian there is no God.

At 9:34 AM, September 10, 2016, Blogger David Friedman said...

I am not trying to persuade him that man is not responsible for climate change–that was not what the argument was about. I am trying to persuade him that we have no good reason to expect climate change to reduce agricultural output below what it would otherwise be and no good evidence that it has done so.

As should have been obvious if you had treated my post as an argument rather than judging it as "my side good, their side bad."

At 9:40 AM, September 10, 2016, Blogger John David Galt said...

The key phrase "in the same ways and in the same places as we have done in the past" blows the rest of the piece away.

A warmer earth could conceivably put a few tropical island countries under water, though even the alarmist estimates I've seen didn't predict more than a few centimeters per century -- anybody who can't build the dikes up faster than that deserves to go under.

Meanwhile it would make vast areas of Canada and Siberia both arable and comfortable to live in.

@Fred: To judge the "climate change agenda" it isn't important whether climate change is man's fault or not. The question that matters is, what is the cheapest, easiest, and fastest way we can protect ourselves from its ill effects, assuming there are any at all. Sacrificing our rich civilization by cutting way back on energy use is unlikely to be that best way. Gregory Benford's scheme is only one of many alternatives.

At 2:55 PM, September 10, 2016, Blogger Fred Mangels said...

Points well made, all.

At 4:24 PM, September 10, 2016, Blogger Xerographica said...

Of course climate change threatens the food supply. Change threatens the supply of everything. Thanks to change... we're here and dinosaurs are not here. The optimum changed and mammals were closer to the new optimum.

In that case the climate changed relatively quickly. And sure you can argue that humans aren't changing the climate so fast that our crops won't be able to adapt. But I think it's far more important to consider how the system prevents our energy sources from being naturally diversified.

The problem with command economies is that far too many eggs are placed in far too few baskets. Our government is a command economy that exerts a huge amount of control on the supply of energy. So do you think that our current energy supply is as diverse as it would naturally be? No? Yet you sure seem to spend quite a bit of time defending it.

Let's say that people could choose where their taxes go. What would happen to the supply of energy? Would it become more diverse... or less diverse? Of course it would become more diverse. It would become a lot more diverse. And that would be a really good thing. It would facilitate the optimal evolution of energy.

With the current system... of course the government is going to mess up the supply of energy. And of course this is going to have unintended and detrimental consequences. Please allocate your energy to showing people these unintended and detrimental consequences. Or not. Feel free continuing to pretend that, thanks to the government, the supply of energy is optimal and wonderful and we have absolutely nothing to worry about.

At 6:22 PM, September 10, 2016, Anonymous Power Child said...


What do you think of the idea of AGW alarmism (and perhaps other forms of environmentalism) as a pressure safety valve for the natural conservative impulses of people who would otherwise recoil in horror at the notion they're being conservative about anything?

At 4:26 AM, September 11, 2016, Anonymous Anonymous said...

There is no climate stasis... in current parlance, 'climate change' is the CLAIM that changes in climate are being brought about over and above natural variation from accelerated rate of global warming cause by CO2 emissions from fossil fuels.

Simply correlating a variation in crop output with a claim and thus attributing cause to that claim, is logical fallacy - is it not?


Do global yields of crops take into account the switch by farmers from producing food crops to producing crops for biofuels as encouraged by Government subsidies to 'fight' the alleged climate change? A switch that was sufficiently significant to affect global prices.

What other factors might affect global crop output - wars, local droughts, other natural catastrophe such as Tsunami, Earthquakes, for example? Were these allowed for?

Since atmospheric CO2 concentrations was not excluded, as noted, it is likely other factors were too.

The climate change debate is an interesting one, in that the 'change' is contingent on an increasing RATE of global warming, yet there has been no increase in the rate of global warming since 1995 and a decline over the last few years. The sudden increased rate of global warming that set this hare running occurred between 1979 and 1995, then stopped despite increased rate of CO2 emissions.

The net increase in global warming for the period 1979 to date, is nearly zero.

How then can the effect (climate change) be present in the absence of its cause (accelerating global warming)?

And that being so - how can 'climate change' have affected crop production?

At 4:28 AM, September 11, 2016, Anonymous Anonymous said...


"Since atmospheric CO2 concentrations was not excluded, as noted, it is likely other factors were too."

Should be:

Since atmospheric CO2 concentrations was excluded, as noted, it is likely other factors were too.

At 2:23 PM, September 11, 2016, Anonymous Anonymous said...

There is a way to reduce global agricultural output. If everyone were to adhere to veganism, then domestic animals would disappear (no more cows, pigs, chicken, sheep or donkeys; perhaps we would keep dogs and horses, because they are cute). If there were no animals for meat or hide or bones then there would not be any need to grow as much crops as we do now.

This would affect insects and birds and other animals that feed on crops. I suspect there would be less humans, as a vegan diet is not adequate for the reproductive purposes of omnivorous animals.

Of course, we would not use combustion of any kind of fuel as a means to produce energy. In fact, we would require less energy because diet would be raw and everyone would just happilly walk from one place to another.

Then the superintelligent surviving humans would measure the atmospheric CO2 level, and perhaps would find that it was the same if not more than today, in the dark ages of unhampered laissez-faire capitalism and hideous egoism. That would be problematic.

Or perhaps the level CO2 in this ecologistic utopia would be in the optimal level to allow horses to evolve into unicorns and pegasi. And, if horses can grow feathered wings, why not humans?

A reduction in agricultural output would only be horrifying to those who don't want to see people and animals starve. Whimsical people.

At 7:18 AM, September 12, 2016, Blogger montestruc said...

Interesting book that shows in the long term without human intervention plants on earth will die from lack of CO2

At 7:45 AM, September 12, 2016, Blogger TheVidra said...

I had always wondered why the entire climate change (ex global warming) conversation focuses only on the costs, while ignoring the potential benefits of the phenomenon. The cynic in me might say the focus on doomsday scenarios is due to "vested interests". The naive in me wants to recognize that Americans have a visceral fear of the heat (air conditioning in all months, everywhere, ice in every drink, light clothing made out of cotton or polyester worn year round) - so the idea of the planet warming triggers certain phobias.

At 9:45 PM, September 12, 2016, Anonymous Anonymous said...

How many CO2 emissions are attributable to Microsoft Windows use? Software companies are not responsible of the use that humans give to their programs. But a growing number of people believe today that humans are just machines, like all animals, and that our actions are determined by the software that emerges from our brains. Therefore humans, like software companies, are not responsible for the damages. It was just bound to happen.

At 12:07 AM, September 13, 2016, Anonymous js290 said...

If there was only one variable that affected climate, it's not CO2, it's the output of the Sun. If there was a second variable that affected climate, it's the kinematics of the Earth about the Sun. Neither of which should be considered constant. What kind of society would deceive itself with calendars into believing climate is constant and predictable? One that's getting ready to double down on more command-and-control.

"Every culture that has depended on annual plants for their staple food crops has collapsed." @RestorationAgD

"Name one ecosystem that is better off for having agriculture moved into it?" Toby Hemenway

At 2:54 PM, September 13, 2016, Blogger David Friedman said...

The Vidra:

I think part of it is a conservative bias. Change is presumptively bad.

Beyond that, the catastrophic narrative makes for more exciting news stories, and it provides an argument for doing things that people pushing it are already in favor of doing.

At 10:11 PM, September 13, 2016, Anonymous RJ Miller said...

I too can't help but get a Julian Simon vibe from this particular question, in the sense that we're probably underestimating how agriculture would differ in response to a change in climate patterns (e.g. GMO advances, vertical farming, etc). It's never a good idea to view present practices as indefinitely static.

But something else we have to take into account regarding climate change is how that change is *distributed* throughout the globe. A one degree increase in temperature in arctic regions is certainly going to have a different impact on agriculture than a change in actual farming areas. I'm not an expert on this topic either, but it seems like all general discussion assumes that temperature change has been globally uniform.

On a related note David, have you seen this NYT mini-documentary about Paul Ehrlich's failed predictions?

At 12:57 AM, September 14, 2016, Blogger David Friedman said...

RJ: I haven't seen the documentary. I knew Simon and had a chapter in one of his books.

So far as distribution of temperature increases, the general rule is that they are larger in cold times and places than in hot. The reason is that water vapor is a greenhouse gas, the more of one greenhouse gas in the atmosphere the less the effect of adding another, and the colder it is the less water vapor in the air.

That means that the pattern is biased in our favor, since warmth is typically a good thing when it's cold and a bad thing when it's hot.

At 9:57 AM, September 14, 2016, Blogger Josiah Neeley said...

Redoing the calculation using only the two effects we knew were associated with AGW, warming and increased CO2 concentration, made the percentage increase in rice equal to the decrease in maize, the increase in soybeans larger than the decrease in wheat.

Unless I'm missing something, what should matter here are not the percentage changes but the change in total output. When you do that, it looks like the reduction in wheat production from increased temp + CO2 is about three times as much as the increase in soybean production from those factors (rice and maize roughly cancel each other out).

At 11:41 AM, September 14, 2016, Blogger J Oliver said...

Also per acre yields of crops is very much a function of the price the grower can get for the crop. The typical average USA yield per acre of corn is 175.1 but the record is 532.0271 bushels per acre to get to that type of yield requires inputs that raise the cost above the price. Most of the world is well bellow the USA yield. I cannot find a link but I have heard that world per acre yields are growing faster than population.

So if AGW reduces yields and that causes a price rise, farmers will use more inputs and increase the yields to meet the demand.

At 11:53 AM, September 14, 2016, Blogger J Oliver said...

One point other point, I think that if you taxed co2 put into the air and paid out the proceeds of the tax for removal of co2 from the air (enhanced weathering, biochar, deep ocean iron fertilization) that it would be surprisingly cheap to reach equilibrium.

It still may be cheaper to live AGW though.

At 3:23 PM, September 17, 2016, Blogger David Friedman said...


A point I didn't discuss in the post but should perhaps add is how much of each crop is used to feed humans. For maize it's only about 15%, with the rest going for animal feed and biofuels. For rice it's 85%. Wheat it's 70%.

Put all of those numbers in, leaving out soybeans because I don't have the figure for them, and it works out as just about zero net effect on the food supply.

At 9:11 PM, February 16, 2017, Blogger The Skip Bureau said...

Another thing that concerns me about the AGW crowd is there complete unwillingness to consider engineering fixes. In another comment, I pointed out they won't consider benefits from a warming world, such as increased rainfall and possibly reduced weather extremes, which is a defensible position to take.

Increased rainfall would make lots more land arable, for instance. It's not just the warming of the areas in Canada and northern Asia that are huge and would be arable in a warmer climate, with production equal to the Midwestern US, but the deserts would be greener as well, leading to the ability to grow crops there. They grow crops in West Texas, after all.

Also, at one point, a proposal was put out for a large mylar film to be placed between the earth and the sun, which could be furled and unfurled as necessary, which would completely negate any need to deal with CO2 at all, even presuming CO2 was the tail of the tiger. Such a solution would certainly be cheaper than ruining the entire world's economy.


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