Wednesday, February 16, 2011

Climate Change Wrecks Agricultural Yields! (Not)


It has become pretty common to hear otherwise well informed left-leaning observers claim that climate change is affecting food production. Krugman said the other week
Why is production down? Most of the decline in world wheat production, and about half of the total decline in grain production, has taken place in the former Soviet Union — mainly Russia, Ukraine, and Kazakhstan. And we know what that’s about: an incredible, unprecedented heat wave.

Obligatory disclaimer: no one event can be definitively assigned to climate change, just as you can’t necessarily claim that any one of the fender-benders taking place right now in central New Jersey was caused by the sheet of black ice currently coating our roads. But it sure looks like climate change is a major culprit. And it’s not just the FSU: extreme weather elsewhere, which again is the sort of thing you should expect from climate change, has played a role in bad harvest around the world.
And here's John Podesta and Jake Caldwell in Foreign Policy last summer:
There was already little margin for error in a world where, for the first time in history, 1 billion people are suffering from chronic hunger. But the fragility of world food markets has been underscored by the tragic events of this summer.

The brutal wildfires and crippling drought in Russia are decimating wheat crops and prompting shortsighted export bans. The ongoing floods and widespread crop destruction in Pakistan are creating a massive humanitarian crisis that has left more than 1,600 dead and some 16 million homeless and hungry in a region vital to U.S. national security. These and other climate crises trigger widespread food-price volatility, disproportionately and relentlessly devastating the world's poor.
This was something Joe Romm linked to in a scary piece today. But, for the ultimate fix of climate doom, you should subscribe to Desdemona Despair, where you'll try to swallow the output of a well-cranked firehose of news stories about floods and droughts and harvest failures all around the world.

Now clearly, there are concerns about climate change affecting agriculture in the future.  But look at the FAO's global data for average cereal yields, for example:


See the big slowdown?  Me neither.  In addition to the data (blue), I've added a linear trend, which explains 99.132% of the variance in the data, and a quadratic trend, which explains a completely insignificant additional 0.16% of the trend.

So, clearly, the overwhelming story in global agricultural yields is this: improving agricultural technology has increased yields at a steady, reliable pace - they have more than doubled over the last 50 years.  There just is absolutely no support in the data for the idea that climate change, or any other negative or scary factor you care to name - eroding soil, depleting aquifers, peaking oil supplies - is causing the agricultural yield curve to start bending downward.  Maybe they will in the future, but it sure isn't happening yet.

But wait! you say.  Aren't the wiggles in that graph getting bigger?  Isn't wild and crazy weather all round the planet at least making harvests less predictable?

Well, given that nice straight line being such an excellent fit to the data, we can take the residuals (the difference between the yield each year and what the straight line said should happen), and then ask, how big is the residual as a percentage of the expected value?  That basically is how big the wiggles are as a fraction of the currently expected average yield.

That's this graph:


So you can see that, as a fraction of the whole, the fluctuations in yields are actually going down over time.  Slowly, ok, but still: the worlds harvest's are not only getting bigger, they are getting gradually more predictable, not less.  Wild and crazy weather happened in the past too, and apparently the global agricultural system was more vulnerable to it back then.

So if food prices are at record levels, we have to look elsewhere for the cause: climate change driven yield losses or fluctuations is a non-starter as an explanation.

Update: Graph of the fraction of US corn planted which is then actually harvested.  See comment discussion with kjmclark below.

57 comments:

Mr. Sunshine said...

Sysco declares Force Majeur on 2/8/2011:

ALL OF OUR GROWERS HAVE INVOKED THE ACT OF GOD CLAUSE ON OUR CONTRACTS DUE TO THE FOLLOWING RELEASE. WE WILL BE CONTACTING YOU PERSONALLY TO REVIEW HOW THIS WILL AFFECT OUR CONTRACTED ITEMS WITH YOU GOING FORWARD.

THE DEVASTATING FREEZE IN MEXICO IS WORST FREEZE IN OVER 50 YEARS…

THE EXTREME FREEZING TEMPERATURES HIT A VERY BROAD SECTION OF MAJOR GROWING REGIONS IN MEXICO, FROM HERMOSILLO IN THE NORTH ALL THE WAY SOUTH TO LOS MOCHIS AND EVEN SOUTH OF CULIACAN. THE EARLY REPORTS ARE STILL COMING IN BUT MOST ARE SHOWING LOSSES OF CROPS IN THE RANGE OF 80 TO 100%.

EVEN SHADE HOUSE PRODUCT WAS HIT BY THE EXTREMELY COLD TEMPS. IT WILL TAKE 7-10 DAYS TO HAVE A CLEARER PICTURE FROM GROWERS AND FIELD SUPERVISORS, BUT THESE GROWING REGIONS HAVEN’T HAD COLD LIKE THIS IN OVER A HALF CENTURY. THIS TIME OF YEAR, MEXICO SUPPLIES A SIGNIFICANT PERCENT OF NORTH AMERICA’S ROW CROP VEGETABLES SUCH AS: GREEN BEANS, EGGPLANT, CUCUMBERS, SQUASH, PEPPERS, ASPARAGUS, AND ROUND AND ROMA TOMATOES.

FLORIDA NORMALLY IS A MAJOR SUPPLIER FOR THESE ITEMS AS WELL BUT THEY HAVE ALREADY BEEN STRUCK WITH SEVERE FREEZE DAMAGE IN DECEMBER AND JANUARY AND UP UNTIL NOW HAVE HAD TO PURCHASE PRODUCT OUT OF MEXICO TO FILL THEIR COMMITMENTS, THAT IS NO LONGER AND OPTION.

WITH THE SERIES OF WEATHER DISASTERS THAT HAS OCCURRED IN BOTH OF THESE MAJOR GROWING AREAS WE WILL EXPERIENCE IMMEDIATE VOLATILE PRICES, EXPECTED LIMITED AVAILABILITY, AND MEDIOCRE QUALITY AT BEST. THIS WILL NOT ONLY HAVE AN IMMEDIATE IMPACT ON SUPPLIES, BUT BECAUSE OF VERY STRONG BLOSSOM DROPS, THIS WILL ALSO IMPACT SUPPLIES 30 – 60 DAYS FROM NOW.

SOME GROWERS ARE MEETING WITH THEIR BOARDS RIGHT NOW TO DETERMINE WHETHER THEY SHOULD IMMEDIATELY RE-PLANT, HOPING FOR A HARVEST BY LATE-MARCH-TOEARLY-APRIL, OR WHETHER THEY SHOULD DISC THE FIELDS UNDER AND WAIT FOR ANOTHER SEASON.

Source: Sysco Release/Memo: Mexico Freeze [PDF] http://www.stevequayle.com/News.alert/11_Cosmic/110209.Sysco.Mexico.Freeze.pdf

KLR said...

Climate Change Wrecks Agricultural Yields! (Hasn't Yet)

Fixed that for you.

There's no way the departure from the trend in 1965 was greater than that of 1985, you can tell that from simple eyeballing. Your math is skewed in some fashion here.

How does this break down regionally? Sure they're going gangbusters in Iowa but what about in Pakistan?

All in all, pretty funny stuff, in the devoid-of-context department of humor. Burning coal is good for soybeans, kids!

risa said...

In other news...

Stuart Staniford said...

KLR - the absolute fluctuations are greater more recently. But as a percentage of the harvest they are smaller. One would expect bigger harvests to result in larger absolute fluctuations - if a storm devastates X acres, but now X acres produces twice the yield, the size of the yield fluctuation would be larger. But the percentage would not be.

Stuart Staniford said...

Mr Sunshine:

The fact that there's a disaster in a particular place at a particular time proves absolutely nothing. It's like me linking to, oh, say, the Bangladesh floods and famine of 1974, which killed a million people.

You just can't reason from individual episodes because the temptation to cherry pick what you want to see is too great. You have to look at large scale averages and trends over reasonable periods of time, and if you do that, the evidence of a climate signal is just not there.

between-the-lines said...

I agree with you KLR, this first graph looks very broad brush. It's no use, for example, if US farmers are sqeezing ever higher yields out of their soils at great expense in energy, fertilser and pesticide inputs, if farmers in poor countries are being devastated and forced into ever greater dependence on imports.

Couldn't see the actual graph when I clicked on the link to find out more about the assumptions behind it. Did I miss something?

And these researchers seem to have different figures.

Mr. Sunshine said...

Stuart, I understand the difference between weather and climate, but one must pay attention to one's local weather. When the cost of a flat of tomatoes rises from $9 to $24 in a week, as it has, when they're available, it is relevant.

Of course, the next planting will restore yield from these same fields, and as long as they're available, "green revolution" farming techniques (mechanization, fertilizers, expanding use of GM techniques, herbicides , pesticides, pumped irrigation from aquifers, etc)will continue to increase overall yields. Given the energy invested in modern food production, the climate's role is probably minimal, other than due to local events such as the superbowl freeze.

kjmclark said...

I think there's a problem here. Here's their definition of yield:
"Crop yield

Definition
Harvested production per unit of harvested area for crop products. In most of the cases yield data are not recorded but obtained by dividing the production data by the data on area harvested. Data on yields of permanent crops are not as reliable as those for temporary crops either because most of the area information may correspond to planted area, as for grapes, or because of the scarcity and unreliability of the area figures reported by the countries, as for example for cocoa and coffee."

I had to search their glossary. The problem is that if your crop fails, you often don't harvest it. You just plow it under and plant something else. If you don't harvest it, the yield is not zero, it's just not counted. So if a million acres of wheat in Russia wasn't worth harvesting, it doesn't get recorded as 0 yield for a million acres, it gets recorded as no harvest, and ignored for yield purposes.

between-the-lines said...

"If you don't harvest it, the yield is not zero, it's just not counted."

LOL. Well found kjmclark. This illustrates well a common fallacy of thinking. I remember being at a talk by the botanist Tim Rich where he was trying to explain to some would-be plant recorders that random sampling necessarily entailed their recording grid squares covered by roads, tarmac, concrete etc as NIL. It took them ages to get it, sadly.

Alexander Ac said...

Stuart,

nice post which pretty much shows that food (and oil price) is a fear driven speculation and 2nd phase of market crash is close. The only way why I see you dont see it is that you did not see the first crash (deducing from your conversations with Stoneleigh in 2006 at TOD) :-)

regards,

Alexander

KLR said...

Alright. But there are a preponderance of other factors that should go into such an analysis - how much of this is owing to greater use of land instead of progressing tech; how does it shake out regionally; how has per capita consumption of food changed?

Krugman and Romm, eh? How about academia? crop yield climate change - Google Scholar

Nonlinear temperature effects indicate severe damages to US crop yields under climate change

We find that yields increase with temperature up to 29° C for corn, 30° C for soybeans, and 32° C for cotton but that temperatures above these thresholds are very harmful. The slope of the decline above the optimum is significantly steeper than the incline below it.

So you hit a tipping point beyond which yields plummet, with a 20% decline in corn from 2020-2049 under scenario B1. If there's any validity to that we should know soon enough, assuming linear rise in temp.

Frozen in the North said...

Interestingly Canada's wheat production was off dramatically in 2010, from the 2009 performance... taken as a snapshot it looks terrible, when you realize that 2010 production was still 15% than 2007 production.

I would suggest that with a growing middle class in China, that requires meat rather than vegetable, which is less efficient to produce, we are seeing a shift in the demand/supply equilibrium. Also 2010 was the year of El Nina which always shifts weather patterns.

However, in Northern Africa food prices are clearly having a serious impact, so something is afoot!

Gary said...

It is also interesting to note that the world population has increased by a factor of 2.3 during which time your cereal yields have increased by 2.5 - so we are keeping up with population pressure as well. However, if global inequality is increasing, which it seems to me it is, then we could easily be pushing those at the bottom into starvation when those little fluctuations on your graph push prices up.

John said...

Wait a minute, you can't eat yield! people eat grain (TONS) not yield Tons/Unit Area. Why look at production RATE if you want to claim climate has no impact on Food production? A rising rate tells you NOTHING about total annual harvest:
Global Cereal PRODUCTION fell from 2008 to 2009 from 287 to 219 million tons.

http://www.fao.org/docrep/011/ai482e/ai482e13.htm

Who cares about gloriously monotonically increasing rates, if you have no food on your plate. You know better, why are you touting such nonsense as significant?

ondrej said...

Well, it is average of crop yields, but what about total production?

You can have rising average, but most common going down.

I still have feeling that production in total is stagnating...

Douglas said...

A couple points:

The data do not include 2010, which at least “felt” like a freakish year for the climate. So the Russian drought and Pakistani floods are not included. Not to mention 2011 events in Australia and China.

Another complicating factor is the extent to which people in developing countries are “forced” to rely on commercially produced food, as wild sources of fish, game and produce come under greater pressure. I have no idea the magnitude of this effect -- if it exists at all -- but I do wonder about it. If it does exist it could impact the demand side of things.

But I do think yield per hectare can keep increasing for a while, as the more intensive agriculture practiced in the West becomes more common in developing countries.

Kenyon said...

The anecdotes did seem to pile up a bit this past year, from Russia, Pakistan, Australia, the Mexican freeze, the looming Chinese drought. The sensationalism of the events themselves definitely added drama to all the claims about the impending impact of climate change on the food supply.

Has per capita grain production remained relatively constant over the last few decades?

Stuart Staniford said...

Kjm saith:

The problem is that if your crop fails, you often don't harvest it. You just plow it under and plant something else. If you don't harvest it, the yield is not zero, it's just not counted. So if a million acres of wheat in Russia wasn't worth harvesting, it doesn't get recorded as 0 yield for a million acres, it gets recorded as no harvest, and ignored for yield purposes.

That won't wash either. We already established on Monday that over the same period that yields doubled, "area harvested" increased by about 30%. So there's not much scope for massive weather damaged areas to be hiding the climate signal.

Stuart Staniford said...

Alex:

Yes I did foresee a recession and a credit crunch. I just disagreed with Stoneleigh that it would be the end of the world, as opposed to a bad recession.

Stuart Staniford said...

KLR:

I am not claiming there is no reason to be concerned about the future. I am claiming there is no evidence in the global data so far of a climate signal.

Regionally, there may be, and that's an interesting question to explore. But if so, it's being washed out by gains elsewhere.

Stuart Staniford said...

Douglas:

True the data for 2010 are not yet available. But if 2010 were to be a massive trend break, it would be very hard to attribute that to climate change since climate change has been going on steadily for a number of decades.

kjmclark said...

Stuart, I'm not sure we're talking about the same thing. I'm not saying your point is wrong, I'm saying that you're showing one set of data and saying it means something slightly different, so it's hard to tell. Unless I'm missing something, both today and Monday, you've shown FAO data, which are *harvested* hectares, but you're making it sound like that's *planted* hectares. These are different things. *Harvested* hectares is only that land that was planted and subsequently harvested.

As I pointed out above, when a crop fails, you often don't harvest anything. You just plow the destroyed crop under and report that nothing was harvested. So the harvested hectares should be less than the planted hectares, by the amount that wasn't harvested. That all fits the FAO definitions. There is no yield - not zero, not anything - on hectares not harvested. If anything, you'd check a box to say X hectares had no crop. It shouldn't show up in the yield, since there was no harvest.

So in your chart above from the FAO source, you should probably label it as "Yield on harvested hectares", which is what the FAO is reporting with their data, according to their website. If you think they're really reporting "Yield on planted hectares", you might be right, but that's not what their definition says. I'm not saying that yield on harvested acres isn't rising, or that acres harvested isn't rising.

If you want to say that the climate signal isn't showing up, you'd want to show planted hectares * expected yield, so 'expected harvest', and compare that to actual harvest. Or, you could compare planted hectares to harvested hectares, and yields (harvested) over time. If climate is causing problems, you might find that the difference between planted and harvested acres is increasing, and/or yields (which again, is just the harvest) are falling.

BTW, I sent a question to FAOStats about how they handle destroyed crops for yield calculations. I'll pass along what they say.

Douglas said...

I don't know Stuart. The agricultural revolution has also been going on steadily for a number of decades. But eventually climate change may trump this...you indicate as much in your "maybe they will in the future" comment.

Maybe 2010 is when the trend started to break? We'll know soon enough.

Greg said...

Nice to hear the voice of reason, Stuart!

Hunger and famine have never been due to problems with supply. Distribution has always been the issue, and that's down to politics. This seems unlikely to change over the course of the century. (Russia's response to its crop failure is a warning that this century's politicians know no more than those of the eighteenth century. China's responses to its smaller problems, likewise.)

Let's assume that climate modelling projections are right: Amazonia, the mid-west USA, southern Europe, northern China and cereal-growing Australia become deserts, and northern India becomes barren because of the heatwave problem you discussed last year.

At the same time, the areas that are now cold-temperate and sub-arctic will warm sufficiently to be able to support cereal crops, and the Sahel and East Africa will get increased rainfall. With a small investment -- half a percent of world GDP for a decade, say -- the new areas could be developed to compensate for the losses.

The wild cards are the Asian monsoon and crop disease. If the monsoon becomes very erratic, with two years of intense flooding followed by three years of no rain, that could make things awkward - i.e., require much greater investment in boreal croplands. Similarly an onslaught of "crop superbugs" could cause difficulty for a while. But overall there is no technical reason why we would run short of food.

Of course this is hypothetical. Politics-as-usual will ensure that the transition is extremely fraught - and possibly unsuccessful. The food problem will continue to be one of politics, not production. Just like all the other hard problems we face.

Stuart Staniford said...

Kjm: That idea didn't sound very plausible to me, but I recalled that the USDA NASS separately estimates area planted and harvested. So as a quick check, I grabbed the data for corn (probably the most important US crop) and plotted the ratio. The graph is in the Update in the post above. As you can see, the fraction of plantings that actually gets harvested has been rising in recent decades, not falling.

So absent some other data showing the opposite, this doesn't seem a very promising place for the climate signal to be hiding.

Eric Thurston said...

"I am not claiming there is no reason to be concerned about the future. I am

claiming there is no evidence in the global data so far of a climate signal."


While reading 'Under a Green Sky' by Peter Ward, I came across this: "There is

already significant human mortality from the current greenhouse-induced global

warming of Earth. A 2004 study by scientists at the World Health Organization and

the London School of Hygiene and Tropical Medicine determined that 160,000 people

die every year from the effects of global warming, from malaria to malnutrition,

children in developing nations seemingly the most vulnerable. These numbers could

almost double by the year 2020."

There are probably many more fatalities from climate change related to storms,

heat waves, etc. that are difficult to quantify but nevertheless very real.

It may be that the crop yield statistic is somewhat of a moot point, especially

given the perennially gross mal-distribution of food worldwide and the virtual

certainty that this mal-distribution will get worse as time goes on. Further, I

expect we will see a tipping point in crop yields that could be rather abrupt if

the apparent acceleration of climate change continues.

The study I'm quoting here I see as an 'Early Warning' while the crop yield

figures (and the statistics on de-leveraging you cited yesterday) seem to me more

like an 'Optimistic Exception'

Alexander Ac said...

Stuart,

point taken. So lets see how the things play out in the near future...

I still think nothing has been truly resolved since the first crash. Neither do I think current growth in liquids is long-lasting and structural problems are probably much worse (debt etc...)

Cheers,
Alex

Stuart Staniford said...

Eric:

I'm not taking a general climate contrarian line. I agree messing with the climate is a terrible idea, and I'm taking significant steps in my own life to lower my own impact on it.

However, my first commitment on this blog is to the truth and to following the data wherever it leads, and I just cannot see the slightest evidence of a climate signal, or any major supply-side problem, in the data on global agricultural production. I accept the evidence that climate change is making weather extremes more common - it just isn't feeding through into global agriculture enough to matter, at least so far.

The overall goal here is to improve our insight into why food commodity prices have spiked up twice in the last three years. And I don't think attributing much of that at all to climate change is sound reasoning. The other obvious suspects are biofuel production and increased meat consumption - and I'd like to somehow quantify how much of each (or whether there are other important factors).

However, I have at least one more climate/food connection post first.

Hypnos said...

It's understandable that many people are taken aback by this kind of data, given the horrible year 2010 was for food.

Stuart, I'd like to hear your opinion on a couple of things then: what do you think is causing the spike in food prices? Is it the events in Russia, Argentina and China, coupled with high oil prices? Or are there fundamental economic reasons - such as distribution, hoarding, or speculation - also at play?

Secondly, do you think the rise in yelds means that so far, technology improvements are keeping abreast of climate change, or that actually climate change has been beneficial to crops so far?

And BTW thanks for your blog posts - so much discussions on global warming and peak oil are based on vague assertions rather than data, that it is extremely refreshing to be able to read articles that are solidly grounded in data-informed reality, and completely devoid of ideology (as shown by your willingness to go against received wisdom on the negative effects of climate change, without being a "skeptic"). Great job!

kjmclark said...

Stuart, that's helpful, though I think we should be much more interested in world production than that of one crop in one advanced country. Again, I'm not saying that your point is wrong, just that the FAO data aren't the whole story, which your update agrees with, though I agree that in the case of US corn, the improving harvest/planted ratio helps make your overall point.

Also in support of your point, there's this article about the Russian drought: http://www.agrimoney.com/news/disastrous-yields-worsen-fears-for-russian-grain--1959.html. Much of that crop apparently *was* harvested, with yields 20%-40% below normal. And this article: http://www.agrimoney.com/news/record-us-wheat-yield-limits-losses-in-world-crop--1962.html, which points out that US wheat yields and production were very good, which helped offset the problems in Russia.

Hal said...

If differences were to show up in some crops between acres planted and acres producing, then it would still not necessarily be a climate signal. It would be more likely that it's a result of commodity row crop production moving into marginal land. That is most likely a result of perceived rises in commodity prices. I'm not necessarily talking about the recent price spikes, but in a trend over the last decade or so to build in long-term price rises by planners.

Drive west on the I-10 and I-20 corridors these days and you will see vast acreages in Arizona and West Texas planted to cotton. Yields are very small and risky, but the price of planting non-irrigated cotton on cheap land makes it worth the risk. That plus increased production out of Africa and Asia has dramatically decreased cotton production in the Mississippi Delta. Meanwhile, predictably, corn and soybean production in the Delta has skyrocketed, which also adds to the increases in those grain crops. (Soy is considered a "grain" in ag econ.)

Also, the Mexican freeze stats have nothing to do with the figures in the OP. Mexico in winter is a big fruit and vegetable producer, and that is, of course what Sysco is all about. No one's going to starve because restaurants can't get enough fresh arugula.

Hal said...

I do have one question to the original point, however. If world grain production is rising linearly, and population is rising exponentially, how can grain production be outstripping population?

Stuart Staniford said...

Hal - population isn't exponential. It's (very roughly) sigmoidal, and is a bit past the inflection point. The growth rate is dropping.

Bytesmiths said...

I'm a bit confused, and admittedly not so wired into the details to be able to post a cogent rebuttal, but might you be "cherry picking" your data a bit here?

I've been seeing things like "grain reserves declining" and "per-capita food production down" and "alternative uses for grain increasing." Sorry I don't have references, but these data don't jive with your data.

In short, most of what I've seen vindicates the WORLD3 model published 40 years ago (Club of Rome, "Limits to Growth"), whereas your data seem to be cornucopian.

Can you explain (for example) why Gail The Actuary is wrong, as linked above?

Eric Thurston said...

Stuart,
Thanks for the considerate response. Like others, I will be watching the crop situation closely --as well as the climate situation-- on into the future.

The more I read on climate change, the scarier it gets.

dimposter said...

If there really are no crop shortages, then maybe the last food price spike really was caused by the great vampire squid wrapped around the face of humanity

dimposter said...

dang, a typo in my html tag.
The last link of course should have been to the rolling stone article

Hal said...

D'oh. I knew that. Or should have. I guess too long since my last ecology class. You don't need to post this. Thanks for the correction.

Bytesmiths said...

Don't let them intimidate you, Hal.

You can only claim growth isn't exponential when it stops being so. Claiming it is sigmoid ignores the fact that it is still growing nearly 2% per year, and is based upon some "prediction" that it will level out at 9 billion mid-century, due to what sociologists call "demographic transition."

Ecology is hard science; sociology (like economics and politics) is soft science. If it comes down to what some sociologist thinks will happen, and limits to trophic exchanges, I'll bet on the physics.

Now if someone had the guts to stand up and say that population growth is not exponential because while it is exponential, we out-strip our food supply and then die off, I might be kinder, but it would still be predicting the future.

Stuart Staniford said...

Bytesmiths:

Here is the data on annual growth rate in world population from the UN population division. Observe that the growth rate peaked in the late sixties and has been declining ever since. It is now almost down to half the peak value. An exponential would have a fixed growth rate (that's pretty much the definition of "exponential")

1950-1955 1.77
1955-1960 1.80
1960-1965 1.94
1965-1970 2.02
1970-1975 1.94
1975-1980 1.77
1980-1985 1.76
1985-1990 1.75
1990-1995 1.54
1995-2000 1.36
2000-2005 1.26
2005-2010 1.18
2010-2015 1.11

kjmclark said...

Two more points on this. First, note that your sample for showing improving harvest/planting was for corn in the US. But the climate map you showed that projected increasing drought for the Mediterranean also shows increasing precipitation for the corn-growing regions of the US. So, if the climate projection is correct, we might expect corn harvests to be improving in the US. But that doesn't necessarily say that harvests will improve in the Mediterranean.

Next, there are some studies on this question. In particular, "Global scale climate–crop yield relationships and the impacts of recent warming", 2007, by David Lobell and Christopher Field, published in Environmental Research Letters. Their conclusion, looking at FAO yields of wheat, rice, maize, soybeans, barley and sorghum, was that measures of growing season temperatures and precipitation explain about 30% of yield variation, and that warming between 1981 and 2002 resulted in an estimated loss of 40 Mt per year, or about $5 billion/yr (2002).

So, there's at least some research that backs up well-informed observers that claim that climate change is affecting food production, but you're still right that, so far, it isn't "wrecking" yields. $5 billion is pretty small potatoes in the world ag market.

Bytesmiths said...

Stuart, I don't have time to fact-check all your data, but I do note that the World Development Indicators database from the World Bank (as reported by Nation Master) says the current population growth rate is 1.4%, rather than the 1.11% that you claim (without reference) that the UN has measured.

I also disagree with your peculiar definition of "exponential" being a "fixed growth rate" -- but so does WikiPedia, which says only that the the rate is proportional to the current value. Thus, any growth expressed as a percentage of current population is, by definition, exponential.

You argued that, because the growth rate conformed to a particular curve (sigmoid function), it could not be exponential. However, there is nothing mutually exclusive between these two terms -- unless population change stops from being a function of the current population, it is still exponential, no matter what curve it may appear to fit.

Contrast this with a linear growth rate, in which some quantity increases by a fixed increment. Perhaps that's what you were thinking of when you used the word "fixed."

Kamil said...

Another important question is How much the CO2 in the atmosphere contributes to the global warming? In my opinion CO2 contribution is not significant and it helps the plants. How reliable is IPCC? Have you read about climategate? http://en.wikipedia.org/wiki/Climatic_Research_Unit_email_controversy

Stuart Staniford said...

Kamil

Yes. My opinion is that people who believe human CO(2) emissions aren't contributing to global warming are roughly on an intellectual level with people who believe that the earth is flat, or that the moon is made of green cheese, and are not worth the time to debate with. Sorry to be so blunt, but you might as well know where i stand.

Kamil said...

I know where you stand. Can you put some arguments, or is it only a belief? Have you seen the data prooving it?
I agree on global warming, but how can you be so sure about the main causes?

The main influences on weather are the Sun's radiance, the Earth's orbit, the continents setting. Other influences include greenhouse effect, the main greenhouse gas is water vapor 36–70%. CO2 has only 9–26% influence on greenhouse, and it's concentration is rising very slowly, about 2.2 ppm per year.

Stuart Staniford said...

Kamil - as I said - I have no more interest in debating it than I have the moon/green cheese hypothesis. You'll have to find somewhere else to have that discussion. There are plenty of fora on the net that are happy to rehash that stuff endlessly.

Kamil said...

Stuart, I am sorry to violate your article. Maybe you can forgive me and next time your will respond with facts or arguments not with bullshit. I am not looking for a fight, I am looking for the truth.

Bytesmiths said...

Kamil, I understand how Stuart feels. He is weary of the denial.

If you are truly interested in the truth, I suggest the following WikiPedia page as a good starting place. From there, you can follow lots of references.

It is unfortunate that you used the word "bullshit," because that is totally meaningless, and is in fact something that can equally be said of anthropogenic climate change deniers.

Like Stuart, I have zero interest in debating that topic. If you are looking for argument, the WikiPedia page should have plenty of links where you can troll for arguments.

Kamil said...

The comparision of moon/green cheese hypothesis to global warming and it's causes is IMO bullshit, because the causes of global warming are not that clear and are only expressed with probability not exact. I am not that good in english, I don't want to insult anyone.
Thank you for the link. I didn't know there are climate change deniers, I thought everyone (big majority) is aware that the climate is changing in time.

Every scientific thesis has to be verifiable, prove able. CO2 influence on global warming is not certain, that is why I expressed my opinion.

Bytesmiths said...

"Every scientific thesis has to be verifiable, provable."

Kamil, have you actually studied science and the scientific method? Or are you drinking the "prove it" kool-aid of the deniers?

Science doesn't work like that. Things we take for granted, like gravity, are not "provable," and science often entertains "thought experiments" to the contrary of such self-evident things as gravity.

Anthropogenic climate change is a theory. Like evolution. Like gravity. It has a preponderance of evidence in its favour, but if you want it "proved" or "verified," you need to come up with a control and an experiment. Unfortunately, when you're dealing with the Earth or a human life, you can't "verify" or "prove" such things; you just continue accumulating evidence.

If you look at that link I posted, you'll see plenty of evidence, and a near-concensus of scientists who accept the theory just as soundly as they accept gravity.

Kamil said...

I have studied science, it works with hypothesis, but accepts it as a fact only if that hypothesis is proved.

Gravity is provable, by experiments. Gravity is not self evident, it requires 4 dimensional thinking as we understand it now.
Darwins theory of evolution was experimentaly proved.

"It has a preponderance of evidence in its favour" - I would say more people supports anthropogenic climate change. I admit that humans have inlfuence on climate, the dispute is here about how much.

What is needed to be done is a political question, nothing to do with science.

Bytesmiths said...

Kamil, not to be argumentative, but "correlation is not causation." If you let go of something and it falls, that does not "prove" gravity exists.

Take Newton's laws of motion. One could "prove" them by experimentation -- and one would be wrong!

Einstein came along and demonstrated that Newtonian motion was only true within a limited frame of reference, but not as one approached the speed of light.

The current theory is that gravity is caused by the Higgs Boson. But that may only be a special case, just as Newtonian motion is just a special case of General Relativity.

You write "What is needed to be done is a political question, nothing to do with science," and yet before, you wrote "Every scientific thesis has to be verifiable, proveable. CO2 influence on global warming is not certain."

So now I'm confused. Are you changing the rules when you don't like them? When someone shows you that almost all scientists agree, you say it is now a political question? I guess I don't understand what you expect.

Kamil said...

Newton's gravity can be proved by observation of planet movement around the Sun same as Einstein's. This experiment has of course it's error and the theory is true within the error margin. This is prety good for practical use.

I am not changing rules. To be done by people is political, because people are driven by politics.
If scientist agree on something that is their opinion. If it can be verified by an experiment (with error) everyone can make that experiment and prove it to (her)himself, or other people.
CO2 influence on global warming can not be proved by any experiment. If something is not proveable, it is considered unknown. We don't know how much is the influence of CO2 on global warming.

If we want to emit CO2 or not is a political choise, not scientific. Politicians makes those decisions, scientists are only looking for the patterns of the nature. Politics decides, what is good and what is wrong (makes laws).

Hal said...

Hey< Kamil, we WERE having a discussion here about whether climate change (which you claim to recognize) was affecting food production. The owner of the blog asked you not to argue the unrelated issue of causation. So not only have you demonstrated yourself as dense as a brick, you're pretty rude to boot.

Stuart, it's amazing to me how much math I've lost since finishing school. I'm going to go off and do some reading on "growth rates" now.

Kamil said...

Thank you Hal, you redirected me back to topic.
So my conviction is that high CO2 levels in air helped the plants to grow. This contributed to the rise of agricultural Yealds.
The growing consumption of CO2 in atmosphere supports this: http://4.bp.blogspot.com/_VM8D_181RjE/S9-N1EOydaI/AAAAAAAAAEY/sW5HT9XfTWo/s1600/C%25_in_atm.jpg

It is also known, that plants need warmth for producing, a little increase in global temperatures, could helped too.

But I think the most contribution to this growing production is made by fosil fuels used to cultivate the soil and used for fertilizers, pesticides production on a bigger scale.

BOP said...

Douglas said:
But I do think yield per hectare can keep increasing for a while, as the more intensive agriculture practiced in the West becomes more common in developing countries.

I suspect this is a key issue. If the growth in yield is being "fueled" by the increasing adoption of energy intensive western agricultural practices then at some point this will intersect with emerging market demand for transport fuels and world oil depletion rates.

Cheers!

Kyle said...

Nice graphs.

Obviously, increasing production means there is no problem, and never will be.

Ten years ago, we could plot similar graphs to "prove" that peak oil wasn't an issue.

It's rather odd the way peak oilers and climate change people each try to either deny or downplay the significance of the other issue. It's like the Pauli Exclusion Principle but for Problems, instead - only one problem may occupy a person's mental space at any time.