Global Warming to Threaten California Fruits and Nuts?

I found this press release on the UC Davis website interesting, because it discusses something new to me, “winter chill”. I found it interesting. But immediately, I thought of this study on irrigation by Dr. John Christy of the University of Alabama, Huntsville.

Irrigation most likely to blame for Central California warming

Given that the UC Davis researchers seem to have only looked at temperature records to establish trends, it looks like they may have missed a significant contributor to the trends – increased humidity due to irrigation. – Anthony

From UC Davis News: Warming Climate Threatens California Fruit and Nut Production

July 21, 2009

Photo: cherry

No more cherry picking?

Winter chill, a vital climatic trigger for many tree crops, is likely to decrease by more than 50 percent during this century as global climate warms, making California no longer suitable for growing many fruit and nut crops, according to a team of researchers from the University of California, Davis, and the University of Washington.

In some parts of California’s agriculturally rich Central Valley, winter chill has already declined by nearly 30 percent, the researchers found.

“Depending on the pace of winter chill decline, the consequences for California’s fruit and nut industries could be devastating,” said Minghua Zhang, a professor of environmental and resource science at UC Davis.

Also collaborating on the study were Eike Luedeling, a postdoctoral fellow in UC Davis’ Department of Plant Sciences and UC Davis graduate Evan H. Girvetz, who is now a postdoctoral research associate at the University of Washington, Seattle. Their study  appears July 22 in the online journal PLoS ONE.

The study is the first to map winter chill projections for all of California, which is home to nearly 3 million acres of fruit and nut trees that require chilling. The combined production value of these crops was $7.8 billion in 2007, according to the California Department of Food and Agriculture.

“Our findings suggest that California’s fruit and nut industry will need to develop new tree cultivars with reduced chilling requirements and new management strategies for breaking dormancy in years of insufficient winter chill,” Luedeling said.

About winter chill

Most fruit and nut trees from nontropical locations avoid cold injury in the winter by losing their leaves in the fall and entering a dormant state that lasts through late fall and winter.

In order to break dormancy and resume growth, the trees must receive a certain amount of winter chill, traditionally expressed as the number of winter chilling hours between 32 and 45 degrees Fahrenheit. Each species or cultivar is assumed to have a specific chilling requirement, which needs to be fulfilled every winter.

Insufficient winter chill plays havoc with flowering time, which is particularly critical for trees such as walnuts and pistachios that depend on male and female flowering occurring at the same time to ensure pollination and a normal yield.

Planning for a warmer future

Fruit and nut growers commonly use established mathematical models to select tree varieties whose winter chill requirements match conditions of their local area. However, those mathematical models were calibrated based on past temperature conditions, and establishing chilling requirements may not remain valid in the future, the researchers say. Growers will need to include likely future changes in winter chill in their management decisions.

“Since orchards often remain in production for decades, it is important that growers now consider whether there will be sufficient winter chill in the future to support the same tree varieties throughout their producing lifetime,” Zhang said.

To provide accurate projections of winter chill, the researchers used hourly and daily temperature records from 1950 and 2000, as well as 18 climate scenarios projected for later in the 21st century.

They introduced the concept of “safe winter chill,” the amount of chilling that can be safely expected in 90 percent of all years. They calculated the amount of safe winter chill for each scenario and also quantified the change in area of a safe winter chill for certain crop species.

New findings

The researchers found that in all projected scenarios, the winter chill in California declined substantially over time. Their analysis in the Central Valley, where most of the state’s fruit and nut production is located, found that between 1950 and 2000, winter chill had already declined by up to 30 percent in some regions.

Using data from climate models developed for the Intergovernmental Panel on Climate Change Fourth Assessment Report (2007), the researchers projected that winter chill will have declined from the 1950 baseline by as much as 60 percent by the middle of this century and by up to 80 percent by the end of the century.

Their findings indicate that by the year 2000, winter chill had already declined to the point that only 4 percent of the Central Valley was still suitable for growing apples, cherries and pears — all of which have high demand for winter chill.

The researchers project that by the end of the 21st century, the Central Valley might no longer be suitable for growing walnuts, pistachios, peaches, apricots, plums and cherries.

“The effects will be felt by growers of many crops, especially those who specialize in producing high-chill species and varieties,” Luedeling said. “We expect almost all tree crops to be affected by these changes, with almonds and pomegranates likely to be impacted the least because they have low winter chill requirements.”

Developing alternatives

The research team noted that growers may be able change some orchard management practices involving planting density, pruning and irrigation to alleviate the decline in winter chill. Another option would be transitioning to different tree species or varieties that do not demand as much winter chill.

There are also agricultural chemicals that can be used to partially make up for the lack of sufficient chilling in many crops, such as cherries. A better understanding of the physiological and genetic basis of plant dormancy, which is still relatively poorly understood, might point to additional strategies to manage tree dormancy, which will help growers cope with the agro-climatic challenges that lie ahead, the researchers suggested.

Funding for this study was provided by the California Department of Food and Agriculture and The Nature Conservancy.

About UC Davis

For 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world. Located close to the state capital, UC Davis has 31,000 students, an annual research budget that exceeds $500 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges — Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science — and advanced degrees from six professional schools — Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.

Media contact(s):

• Minghua Zhang, Land, Air and Water Resources, (530) 752-4953,

• Eike Luedeling, Plant Sciences, (530) 574-3794,

• Pat Bailey, UC Davis News Service, (530) 752-9843,


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Antonio San

And THIS is called science?


Cold Snap Threatens California Citrus Crop

Already battered by an early winter storm that delivered heavy rain, snow and low temperatures, California is bracing for more unseasonably cold weather that poses a threat to the state’s big citrus crop.
Joel Nelsen, president of California Citrus Mutual, the industry trade association, said temperatures could drop to the upper 20s by tonight, leaving the potential for enormous economic damage. About 85% of the 64 million cartons of fruit produced annually in California’s San Joaquin Valley are still on the tree, he said.

Seems there was plenty of “winter chill” last winter.
Here we have another example of people attempting to influence policy (in this case influence crop selection policy of farmers) by using models that have proved incorrect year after year.

Using data from climate models developed for the Intergovernmental Panel on Climate Change Fourth Assessment Report (2007), the researchers projected that winter chill will have declined from the 1950 baseline by as much as 60 percent by the middle of this century and by up to 80 percent by the end of the century.

There has never been a climate model produced that has accurately predicted temperatures that far in advance. Every single one has proved wrong. Why are these people insistent on using the output of these models so far ahead as if they represent any relation to reality?


The authors of that “study” need to be taken by the hand to a computer, navigated to NOAA’s NCDC site and show that continental US temperatures have been declining at a rate of 8 degrees per century over the past 10 years. That is using the government’s own data collected using a network that is biased warm due to siting issues of the recording stations. If that kind of cooling keeps up another 10 years, their problem is certainly going to be “winter chill” but not of the sort they imagine.


In the long run reality always win over computermodels!
Especially due to the fact that computers can’t help if the programmers aren’t up to the standard ‘we’ had in early 70’s when I myself studied for and became Systemprogrammer….
Especially when the computers can’t help the old known fact that the output data can’t be better than the input….

Farmers who act on the recommendations of the IPCC and The Nature Conservancy are few and foolish. UC Davis is well-respected, but they are doing their best to shoot themselves in the foot.


The only nuts in California are the idiots who are repealing the protection for Agricultural land (Williamson Act?). So they can be swooped up by developers or sold to foreign interests.
UC Davis would do well to read up on the incessant winds from the period mid 1860’s to mid 1890’s. They portend the same cooling now as they did then.
Coming back to back, are these two items related?


We should regard the regional projections of the chosen climate models as “sufficiently uncertain”
In support of your Irrigation hypothesis it is worth noticing the origin of the data:
“We obtained records of hourly temperatures
for all 205 (active and inactive) stations of the California Irrigation
Management Information System [CIMIS; 29].”

For as long as there have been farmers, there has been complaints about the weather.

Allan M

“The researchers found that in all projected scenarios,” “IPCC”
No need to worry then.
Just who or what are the nuts.

Alec, a.k.a Daffy Duck

Hmmm…have you seen the multi-state press release from the Union of Concerned Scientists???
July 28, 2009
Unchecked Global Warming Would Mean More Heat Waves, More Flooding, and Reduced Crop Yields in [INSERT STATE NAME HERE], New Report Finds
Congress Considering Legislation that Could Help [Insert State Name Here] and the Rest of the Nation Avoid Worst Effects
CHICAGO (July 28, 2009) — If the United States does not significantly curb heat-trapping emissions, global warming will seriously harm [Insert State Name Here] climate and economy, according to a new peer-reviewed report released today by the Union of Concerned Scientists (UCS). The report also found that a combination of clean energy policies—such as those currently under consideration by the U.S. Senate—would help blunt the extent and severity of global warming in [Insert State Name Here] and nationally….
For Missouri, Press #1
For Indiana, Press#2:
For Minnesota, Press #3
For Ohio, Press #4

Geoff Sherrington

So the farmers grow other crops if the predictions eventuate. Might relieve some boredom and add to skills. It’s a bit precious to state production $ now as if they will all be lost in the future. Why, the next lot of crop selection might be much more valuable and profitable. Always look on the bright side.


Delusional like most if not all forms of prophecy


“To provide accurate projections of winter chill, the researchers used hourly and daily temperature records from 1950 and 2000, as well as 18 climate scenarios projected for later in the 21st century.”
I’m almost embarrased to ask this, but having learned that everything, no matter how unbelievable or outlandish, is possible, especially in this realm, is that a typo in the above statement, and should it really say “…from 1950 up to 2000”? They surely didn’t use just two year’s worth of data for this study?


There is an english phrase which describes these authors well and which they have put in there title.
A bunch of fruits and nutcases

layne Blanchard

Didn’t CA already decide the Central Valley and it’s entire crop are no longer important? Didn’t they cut off the flow of irrigation to the entire central valley to save the tiny Delta Smelt? I think the solution here is to paint all the barns and silos in the central valley white! 🙂


OT, perhaps, but this Canadian radio interview with respected Environmentalist
Lawrence Soloman is, IMHO, unmissable! It’s nearly an hour long but its the clearest explanation I’ve ever heard about the background to the superstition of AGW and the dangers to the Envirnment posed by anti-carbon activities.

Shawn Whelan

And from the latest fish before people report.
Turning off the water to save the smelt and starving the people.
Mr. Howitt estimates lost farm revenue in the San Joaquin Valley could top $2-billion this year and will suck as many as 80,000 jobs out of its already-battered economy.
“This is one of the classic, really difficult trade-offs we are faced with in hard times: environmental values versus human suffering,” he says.
“The rest of California should care about this because what’s happening in Fresno is a forerunner of the essential environmental and economic debate that we’re going to have because our environmental rules were set up before people were confronted with the real effects of an economic downturn.”
The bottom line, Mr. Howitt says, is that “we are going to have to make fundamental choices. … It’s fish versus jobs and communities.”



And at what point will researchers realize that as long as they continue to stop at 2000, they will have NO credibility?…we’re half way through 2009 already…almost a full decade of data that they chose to ignore. And yes, I got the double-play of “cherry picking” 🙂
Pamela, glad to see you here. Hadn’t seen you post in awhile, and you’re one of the regulars that I enjoy reading. Hope all is well.


Just now broadcast on the BBC’s lunchtime news:
Explaining how the Met Office have been wrong about the last three summers a spokesman said ” it is much easier to predict 50 years ahead than to predict a few months ahead”. I would like to nominate this as a quote for the week.

An Inquirer

Those who live by the IPCC forecasts will “die” by the IPCC forecasts.
There is trouble for those who actually believe and base actions according to AGW forecasts — whether it is planting olive trees in England or trying to kayak to the North Pole. Meanwhile, we are not changing seed-corn maturity dates to a longer growing season; although it would nicely increase our yields if we could count on a longer growing season.

“Winter chill”, is a real phenomenon. I live in Ontario Canada, where there are lots of plants called trilliums. Our main variety of these plants, grandiflorum, can only survive if we have very cold winters, which is why they thrive here.

David Y

Not to be cynical (well, okay maybe a little bit) here, but shouldn’t one early paragraph read:
““Depending on the pace of winter chill decline, the consequences for California’s fruit and nut industries could be devastating,” said Minghua Zhang, a professor of environmental and resource science at UC Davis {WHO RECOGNIZES THE VALUE OF FEAR MONGERING IN ATTRACTING GRANT MONEY AND DOESN’T RECOGNIZE THAT AGRICULTURAL PRACTICES, NOTABLY IN CALIFORNIA, ARE NOT STATIC THROUGH TIME, BUT CHANGE IN ACCORDANCE WITH MARKET DEMANDS/OPPORTUNITIES AND CLIMATE.}
Take a look at all the acreage in the Sierra Foothills that has been used for harvesting walnuts and now grapes and olives (and likely other ‘crops’ by the earlier Native Americans–never mind the ‘harvesting’ of gold from the same areas). Sorry, Professor, but this ain’t the end of the world here. And from here in Sacramento, there’s been PLENTY of chill in winters of late–notably resulting in some serious citrus losses locally.

David Y

Anthony, I’ll understand if you ‘snip’ my comments. This stuff just irks me. Sorry if that came across as character assassination of the good Professor.

Retired Engineer

If they base this on IPCC projections, it is more likely that all the trees will freeze.


“found that between 1950 and 2000, winter chill had already declined by up to 30 percent in some regions.”
So has fruit and nut production decreased by some corresponding amount?
“Each species or cultivar is assumed to have a specific chilling requirement”
You know what they say about assumptions.


“Each species or cultivar is *assumed* to have a specific chilling requirement”
I really don’t understand science where assumption plays a large part in reaching conclusions which are then expressed as fact.

Pamela Gray

They are warning us that California will produce fewer nuts????? And they think this is BAD????

Jim Papsdorf

OT: Drudge Posts Pilmer :
Global warming is the new religion of First World urban elites
Geologist Ian Plimer takes a contrary view, arguing that man-made climate change is a con trick perpetuated by environmentalists
By Jonathan Manthorpe, Vancouver SunJuly 28, 2009


Who are the researchers on this study? What research have they already published? I would like to add their names to my list of prevaricating (you know what I mean) (pseudo)-scientists. And guess what. They used perfect dates to fudge their findings.
California farmers know better. They have signs up along much of I5 informing the millions of drivers how much agriculture has been destroyed/taken out of production by the current politicians.


“A better understanding of the physiological and genetic basis of plant dormancy, *which is still relatively poorly understood*”
And all these predictions rest on poorly understood plant dormancy factors, which are then related to poorly performing computer models of climate? And they’re using a temperature history from poorly sited stations, right? And they’re *assuming* the specific chilling requirements for each species? And the winter chill index is arbitrarily centered around certain temperatures, making the percentage change essentially meaningless?
More like alchemy than science…

Douglas DC

Anyone got idea of the frost line in California? that’s more accurate than ‘winter chill’.
Also, how about Urban Heat Islands-ya think that might be a factor too?
I smell grant money!
The Oakland Fire back in Oct. ’91 was made worse by the dead eucalyptus trees,
that were still scattered about from the nasty winter of ’89. I just missed that little clambake by one week-back in my Aerial Firefighting days..


I moved to Bakersfield in 1950 when the San Joaquin Valley was hot and DRY.
Subsequent “AGW” was caused not by CO2, but by increasing water vapor from increasing irrigation. Since then, the major valley weather stations as found on USHCN show no increase (or slight decline) in mean MAXIMUM temperatures. However, the mean MINIMUM temperatures are rising as much as one degree per decade. To say the general climate is warming is false. The truth is the regional humidity is increasing and affecting the weather, a situation NOT present in areas outside of the Valley.

Jason S.

Can any of the 30% reduction be attributed to the mandatory water rationing handed down from Cal Gov? I know Central Valley farmers are fighting for their lives because of the water shortage. I can’t think of one year over the last decade where there was a winter lacking the right conditions for “safe winter chill”.


I’m looking forward to the next Iceage change or yellowstone caldron showing the world what a real volcano can do. Otherwise worring about it is like stepping out your front door and being hit by a bus. Theres nothing you can do about it.
Is it time for another evolutionary step. Has everything stagnated and we need a push. Has a natural population control begun. This terrarium has become a bit crowded.
Wispers in the dark.
Rob in the US.


The best of your post: “No more cherry picking?” …it will produce great suffering where these are used most: In Boulder, Colorado.
As we all know, PDO changed to cool phase, which means drier weather.
As Aron put it the other day: “Hey kids, repeat after me: warm brings rain, cool brings drought”
We all knew, also, about the Napa valley frozen grapes. What is it happening now?
Last question: IPCC and gwrs. statistics froze at 2000, the y2k bug or just a consequence of all California´s green measures?

Steve Keohane

So science is now extrapolated fantasy, no data, no cause and effect. From what I’ve seen of irrigation effects modulating overnight temps, long term it will increase average of minimum. Haven’t read Cristy’s paper yet, but Anthony covered this with Tucumcari, NM.

George Tobin

At Roger Pielke Sr. ‘s site, he cites a paper that finds cooling from irrigation.
It’s all beyond me. Apparently, if you irrigate a dry area, the additional moisture at night creates net warming but if you irrigate an fairly moist area, the additional daytime evaporation makes for net cooling.
Pielke, Sr.’s favorite points are (a) human impact on climate is lot more complex that CO2 emissions and the scientific approach should reflect that; (b) surface temp measurement is probably a lousy metric–we should use ocean heat content in some uniform fashion. I find these points highly persuasive.


I’m just bemused by the whole study which can be summarised as: IF computer models are correct THEN these particular crops will decline, causing $x worth of losses. This is all so moot anyway, since IF computer models are correct, then human civilization will cease (or so they tell us). It’s like a study that finds that IF an asteroid strikes the earth, then the peanut industry in Tennessee will loose $93,899,00. But IF the models are wrong, then the amount of money lost is zero.
As Geoff Sherringham alluded to in his post, in reality, all that would happen is that a different crop will be substituted. This is just basic economics and really, so much common sense, a commodity that seems to be in short supply. If any conclusion can be drawn at all, it is that Pamela Gray is right on the button when she says – there are already too many nuts in California!

I thought this quote by Thomas Jefferson-possibly the greatest and certainly the earliest keeper of a detailed diary on American Weather-was pertinent
This extract is especially relevant as it refers directly to the problems caused by climate change to fruit growing in the mid 1700’s.
” A change in our climate however is taking place very sensibly. Both heats and colds are become much more moderate within the memory even of the middle-aged. Snows are less frequent and less deep. They do not often lie, below the mountains, more than one, two, or three days, and very rarely a week. They are remembered to have been formerly frequent, deep, and of long continuance. The elderly inform me the earth used to be covered with snow about three months in every year. The rivers, which then seldom failed to freeze over in the course of the winter, scarcely ever do so now. This change has produced an unfortunate fluctuation between heat and cold, in the spring of the year, which is very fatal to fruits. From the year 1741 to 1769, an interval of twenty-eight years, there was no instance of fruit killed by the frost in the neighbourhood of Monticello. An intense cold, produced by constant snows, kept the buds locked up till the sun could obtain, in the spring of the year, so fixed an ascendency as to dissolve those snows, and protect the buds, during their developement, from every danger of returning cold. The accumulated snows of the winter remaining to be dissolved all together in the spring, produced those overflowings of our rivers, so frequent then, and so rare now.
Thomas Jefferson
This is from;
(Go to the second to last paragraph at the end)
Plus ca change…

Fred from Canuckistan . . .

“Global Warming to Threaten California Fruits and Nuts?”
It won’t help to threaten Nancy Pelosi . . . she just ignores them.

F. Ross

Generally I have a lot of respect for UC Davis but in this study …
“Using data from climate models developed for the Intergovernmental Panel on Climate Change Fourth Assessment Report (2007), the researchers projected that winter chill will have declined from the 1950 baseline by as much as 60 percent by the middle of this century and by up to 80 percent by the end of the century.”
[emphasis mine]
Models, models, and yet more models – pretty well says it all.

The biggest threat to agriculture in California are the bureaucrats. Many farms on the west side of the San Joaquin Valley have had to let their crops and orchards go fallow due to the Fed and California Dept. of Water Resources shutting off water supplies from the Sacramento Delta, creating a man-made drought. All because of the plight a little minnow called the Delta Smelt, a dish genetically non-distinct from other minnows found throughout the US. And if that’s not enough, the east side of the valley will see its share of water diminish exponentially as the Powers That Be have forced the continuous release of water from the Friant Dam to revive and restore permanent water flow to the now dry San Joaquin River, in order to restore the migration run of salmon, something even the environmental advocates admit may never happen. Fish are more important than people and jobs. At this rate, the San Joaquin Valley will be a dust bowl within three years. Seeing as we grow as much as 25% percent of the nations food supply, everyone get ready for prices on produce to increase dramatically in the next two years.
Rant Off.


Scientists by their nature generally look at their work with a “black/white” “true/false” perspective. They are not generally good at assessing how species will adapt to changes in their environments.
There were a series of devastating freezes in Florida in the 1970s that nearly wiped out the citrus groves north of Orlando. The industry responded by planting new groves further south. Today there remains an abundant supply of Florida grown oranges and grapefruit.
I am certain that even California’s fruits and nuts will be able to adapt to future climate changes, be they colder or warmer.

Milwaukee Bob

Wow! Glad I read the whole post. Reading just the headline I thought they were talking about some friends of mine in San Francisco….. No really, i do have friends there, having lived there for a long time.
As a matter of fact I remember the day John Muir and I, heading to the Sierras from SF first gazed upon the great San Joaquin Valley in – the spring of 1868 – i think it was. What a sight! Far as the eye could see, north to south, and from our feet to the mountains on our eastern horizon – flowers! Every color imaginable but mostly orange. Poppies! Millions of poppies! Ah yes, I remember it well. Then just a few months later upon our return trip, it became clear why California is called the Golden State – everything had died and dried up and turn to straw. It was a desert! HOT and DRY! As we crossed, we wished for the rains and cool of winter…..
Now, any summer day in Modesto is HOT and MUGGY and I am continually astounded by the massive transformation we have brought forth upon the valley and the CONTINUAL shifting of crops from area to area as conditions AND markets change. Yes, COTTON still reins as KING of the valley but RICE and grapes are not far behind and fruits and nuts continue their LONG decline as a percentage of overall land area. I guess they just don’t do that well in a humid climate…. shame really, their flowering in the spring so reminded me of my days with John….
Alas, time marches on.

dr kill


Fred from Canuckistan . . .

The REAL problem with the California Fruits & Nuts . . . the Fruitcakes & Nutters

Wanna guess how she voted ?


Winter 2006-07
California Freeze Threatens State’s Citrus Crop

State officials said that there was no clear way of knowing yet how much damage had been done from the freeze, which sent temperatures plunging in the teens and 20s from Eureka in the north to near the Mexican border for the last four nights. But farmers in some areas of the Central Valley, the state’s 400-mile long agricultural engine, and further south were reporting a near complete loss of fields full of oranges, lemons and other citrus.

Mid-Spring 2008
Late freeze harms Northern California crops

utter County Agriculture Commissioner Mark Quisenberry says farmers are reporting losses in walnuts, canning tomatoes, peaches, pears and prunes. The county’s prune crop, California’s largest, was hit hardest.
In neighboring Yuba County, prune orchards lost between 10 percent and 100 percent of their fruit. Pear farmers reported 30 percent of their fruit destroyed.
It may take longer to determine the damage to walnuts. Yuba and Sutter counties produce California’s fourth-largest walnut crop.
Read more:

Scott B

When will all of these “scientists” realize that these climate models are basically useless? Look at how weather models were 20-30 years ago. They were not reliable. Only through repeated cycles of verifying their predictions and updating / rewriting the code have they now become reasonably accurate out to 7 days. Yet they still get many details wrong are not reliable except for getting ideas of the overall pattern past 7 days. Yet climate scientists think that our climate is so simple they can plug in some variables and accurately model things out for decades? It just doesn’t make sense. Even if everything was being done properly, it will probably take decades if not centuries to have enough information available to be able to tweak the models to be anything useful. And we’re supposed to make trillion dollar decisions based on this now? Just ridiculous.


This will be the first time in history with so many people complaining that their nuts aren’t cold enough.


Not only do they miss the impacts of irrigation, they are also apparently clueless about all the urbanization along the 99 and 80 corridors. Like there is no heat flux from any of that! Right!