Claim: Fall foliage season may be later, but longer on a warmer Earth

From Princeton University we’ll have to put up with fall colors longer, damn that global warming! Oh, wait, they said “could” and “possibly”.

The researchers also found that the timing of leaf change is more sensitive to temperature in warmer areas than in colder regions -- the more southern the region, the more likely there is to be a delay in leaf coloration. In addition, the nearly 20 species the study reviewed respond differently to the sustained summer conditions projected to occur with climate change. For instance, the particularly sensitive paper birch could change color one to three weeks later by the end of the century, the researchers found. Pictured here is one of the studied species, an American beech, from the Institute Woods. Credit: Photo by Christine Medvigy

The researchers also found that the timing of leaf change is more sensitive to temperature in warmer areas than in colder regions — the more southern the region, the more likely there is to be a delay in leaf coloration. In addition, the nearly 20 species the study reviewed respond differently to the sustained summer conditions projected to occur with climate change. For instance, the particularly sensitive paper birch could change color one to three weeks later by the end of the century, the researchers found. Pictured here is one of the studied species, an American beech, from the Institute Woods. Credit: Photo by Christine Medvigy

The fall foliage season that prompts millions of Americans to undertake jaunts into the countryside each year could come much later and possibly last a little longer within a century, according to new research.

Climate change could postpone fall leaf peeping in some areas of the United States as summer temperatures linger later into the year, Princeton University researchers report in the journal Global Ecology and Biogeography. For instance, the paper birch — a popular foliage tree that is the state tree of New Hampshire — could change color one to three weeks later by the end of the century, the researchers found. Although some trees will be less susceptible to the ongoing heat than the paper birch, the more southern the region, the more likely there is to be a greater overall delay in leaf coloration, the researchers found.

Trees need daily temperatures to be low enough and daylight hours to be short enough to produce the vivid vistas of fall, explained senior author David Medvigy, an assistant professor of geosciences and associated faculty member at the Princeton Environmental Institute. He and first author Su-Jong Jeong, a former Princeton postdoctoral student now at NASA, found that daily temperature and daylight hours can not only be used to predict the timing of leaf coloration, but that the influence of these factors depends on the individual tree species and the specific geographic area.

“We’re really interested in understanding how these systems will change as we experience global warming or climate change,” Medvigy said. “What these results are suggesting is that different locations will change in different ways, and that these differences are actually going to be quite interesting.”

Aside from fall foliage and its economic importance to many areas, the research has broad implications for predicting growing seasons, agricultural productivity and ecosystem productivity, Medvigy said. In particular, a delay in when leaves change color could affect how much carbon an ecosystem removes from the atmosphere, which would partially combat the climate change that caused the delay in the first place, he said.

“When plants have green leaves, they’re doing photosynthesis and taking carbon out of the atmosphere,” Medvigy said. “The longer you have green leaves, the more carbon dioxide you can take out of the atmosphere. At least, that’s how the current thinking goes. So, figuring this out could potentially be important for understanding the impacts of climate change.”

Mark D. Schwartz, a distinguished professor of geography at the University of Wisconsin-Milwaukee, explained that fall leaf coloration marks the end of the growing season in temperate climates, so understanding its current and future cycles illuminates what’s to come for agriculture, water supplies and animal behavior, among many other areas.

Longer or shorter growing seasons influence the type of crops that are planted, the pests that are present, and when animals begin feeding (either on plants or animals that eat plants) and reproducing, said Schwartz, who is familiar with the research but had no role in it. In the western United States particularly, water availability is affected by plants, which are like “little water pumps” that drain soil moisture throughout the entire growing season, he said.

Spring, the onset of the growing season, is well studied, but fall — which is more complex and dependent on geography — is more difficult for scientists to characterize, Schwartz said. Existing models tend to be based on localized data and do not account well for how plants respond to regional fall conditions, he said. Medvigy and Jeong provide valuable, consistent criteria — temperature and light level — for determining leaf coloration that still allow for regional differences, Schwartz said.

“When you get at the growing season you can relate this to a huge number of things. In order to understand how it might change in the future we have to understand how it functions now,” Schwartz said. “This research is a useful addition to what we’re trying to do in terms of improving the way that we model plants. A lot of models that we use in terms of global change are fairly simplistic.”

The study originated when Medvigy, who studies the larger outcome of small-scale interactions between the land and atmosphere, noticed that models had a difficult time explaining the timing of when leaves should change color. He and researchers at the Geophysical Fluid Dynamics Laboratory (GFDL) — which is operated by the National Oceanic and Atmospheric Administration and based on Princeton’s Forrestal Campus — had an idea for solving this problem by using continental-scale data.

“What we noticed from observations was that some trees were keeping their leaves later in the autumn,” Medvigy said. “We tried to make predictions of these phenomena with our models a few years ago, but the results were disappointing. These interesting phenomena have been going on and we had no way of explaining them.”

Medvigy and Jeong sought to test if having information on several species spread over a large area would improve a model’s projections. They collected data on leaf-change dates for several tree species, both in Alaska using the USA National Phenology Network, a free online database of seasonal-change observations recorded by scientists and the public, and in Massachusetts using data and observations from Harvard Forest, a 3,500-acre research property managed by Harvard University.

The species examined were American beech, aspen, black oak, northern red oak, paper birch, red maple, sugar maple and sweet birch. They grouped the tree species into three categories based on their tolerance of shade. For example, birches need a great deal of sunlight; beeches can survive in a shaded environment; and oaks are somewhere in the middle. The nearly 20 species the study reviewed fell neatly into one of these three categories.

Medvigy and Jeong found that prediction modeling for the entire United States indeed improves dramatically when the analyses include data from macro-scale observations, meaning from multiple sites spread over a large area. In addition, they report that temperature and duration of sunlight are both significant factors in determining when tree leaves color in the fall. Previous studies have tended to rely on one factor or the other, not both, Medvigy said. Predictions based on those studies were less effective over broader regions.

The researchers also found that the timing of leaf change is more sensitive to temperature in warmer areas than in colder regions. So if there is an increase in fall temperatures, for example, tree species in Massachusetts will respond to a greater degree than species in Alaska, Medvigy said. Alaska’s foliage season is in September and is unlikely to change in the next 100 years. But Massachusetts’ foliage season will likely occur in November instead of October as it does now, he said. It would take place in southern states even later. With northern climes remaining unchanged and southern areas experiencing coloration later, there is an altogether extended coloration season under climate change, Medvigy said.

Now that Medvigy knows what information is needed to predict what the future holds for leaf coloration, he plans to again collaborate with his colleagues at GFDL to do more sophisticated modeling based on the study results, he said.

“We now have a much better understanding of how temperature, day-length and leaf color are related,” he said. “This understanding will help us make better forecasts for climate, as well as for the basic dynamics of forests. My group is now investigating these issues together with researchers from GFDL.”

###

The paper, “Macroscale prediction of autumn leaf coloration throughout the continental United States,” was published online-ahead-of-print by Global Ecology and Biogeography. The research was supported by the National Oceanic and Atmospheric Administration (grant no. NA08OAR4320752).

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71 thoughts on “Claim: Fall foliage season may be later, but longer on a warmer Earth

  1. So from a previous post tornado season shorter fall colors longer. What’s not to love? Global Warming is there nothing you can’t do?
    You are awesome Global Warming. You too Gaia.

  2. “Oh, wait, they said “could” and “possibly”.”
    yes, all science is probabilities. math and logic are certain.

    • True, but some uncertainties are wider than others, and for you and I we can choose which to take with a grain of salt. There’s a lot of this in climate science. Yogi Berra said it best.

      “It’s tough to make predictions, especially about the future.”

      • I like G.K Chesterton who said.
        “I agree with the Irishman who said he preferred to prophesy after the event.”
        Too bad climate models can’t even get that right.

      • I like the new “lightly significant” term used for the Tornado study. Kinda like significance on a diet. Low cal. Good for you. Maybe someone will market a new statistics program and call it, “Stat Lite”, and market it as the answer for climate data number crunching. Guaranteed to produce the results you need.

    • Astronomical autumn occurs when the Sun is over the equator and spiraling south.
      Meteorological summer is September 1 to November 30. (For folks in the norther hemisphere, of course, I assume you aren’t.
      Foliage season around Concord NH starts in early September, peaks in early October, and November is dark, gray, and chilly. It’s a popular vacation month for the owners of Mom and Pop Motels and B&Bs.

    • I was about to say the same thing – and temperatures in New England and the Northern Plains are not exactly summer like at the moment.

    • Last winter here in western New York State was the longest, coldest winter we’d experienced in a while. We had none of the usual “January thaws.” With the frost being 48″ deep for such an extended period of time, many trees died this year.
      This year, trees started showing signs of Fall color in mid-August, and I covered my tender plants last night as a frost was possible. So if Fall is going to be longer, it’s because it’s starting sooner.

      • 29 deg F here this morning.
        leaves started about 2 weeks ago here (central maine) but are turning very slowly. they never had much sun this year, rained a lot here.

    • The flowering cherry trees have already lost their leaves and some of the other trees are turning yellow in Central MD. Fall is a little early..not late this year. It has been a cool summer.

  3. The paper birch at my house in So Cal (and many others I’ve seen in the neighborhood) have been killed in recent years by an invasive species of boring beetles from Asia. I guess that I won’t have to endure the indignity of the delayed change in foliage color!

  4. Here in New Hampshire the past few foliage season have been a bit disappointing. It may be a bit of acclimatization, as I’ve seen out of state relatives agape at displays I wouldn’t give second chance (and my brother grew up in among the maples and dead elms of NE Ohio).
    Foliage started changing early this year per the consensus. Somehow it always seems to peak around the same week. However, this year we’ve had the chilly September weather that I think gets things on the right path. My neighbor had a maple tree that in 2001 was saturated red, it’s been a relatively drab orange since then. Some of that may be from a leaf fungus that spots up leaves at the end of the season. We’ll see.
    Frost advisory tonight! A few days from now things ought to be looking promising.
    http://wermenh.com/images/autumn_tree.jpg

  5. This is disgusting. It is rank speculation that conjectures a growing season extended by one month in the fall, because of warming. This infers a similar advance of the planting date of one month in the spring or two months added to the present day growing season. A NOAA grant, naturally. Thus winter is reduced by two months. Who would defend crap like this?

  6. So, was anything new, different, unusual, never seen before discovered here? If you remove the global warming / climate change words, the article is just rehashing what I have observed going on all my life. Nothing new discovered here. Same old BS.

  7. They seem to have missed some critical factors such as moisture, exposure and soil types Some trees start turning colour in what appears to me, after 68 years of observation, with the changing daylight hours. Others are less sensitive and often carry leaves well into and through the winter providing browse for a number of animals. Dry years start some trees in our area turning yellow in mid August and if it is hot as well, they drop their leaves early (heat stress). A killing frost also starts many trees and other plants turning colour early even if it warms back up. Tree leaves in moist areas can last longer or shorter depending on whether there is too much moisture or just enough. Monday’s forecast is for 27 C in my area (a couple of weeks after getting 8 inches of snow) and the golfers won’t be finding many balls with all the leaves down on the courses.
    It appears they obtained data from Alaska and Massachusetts. And adjusted it for three species (and some assumed exposure).
    I don’t believe two variables are enough to give good predictions. But perhaps a general trend will be observable if all that CO2 plant food doesn’t throw a spanner into the works.
    I live in a “northern clime” so I guess the comment on Alaska applies: ” Alaska’s foliage season is in September and is unlikely to change in the next 100 years.” So, the animals will graze the leaves as they fall in September like always.
    But the take away is this whole “study” is based on assumptions: “Climate change could postpone fall leaf peeping in some areas of the United States as summer temperatures linger later into the year…”
    Whose assumptions I would ask, and is it going to be dry areas dryer, wet areas wetter, dry areas wetter, or wet areas dryer, and which ones will be warmer and which ones will be cooler? Now, how many variables is that in addition to the multiple tree types, then add in exposure and soil …
    Ok, they may have it right based on their assumptions but are the assumptions correct?
    And if they do get a longer leaf period, they might get a little more of this: https://www.dropbox.com/s/xsqd3kt0ai0mp7f/SnowDay.jpg?dl=0
    Darn Global Warming.
    Still a reasonable paper given the assumptions. But clearly YEARS of study still needed to create a good predictive model, probably right into retirement for them. Good on em. Hug a tree. Reminds me, gotta go finish cutting my winter wood.

  8. The cause was a Nor’easter into a cold arctic airmass moving out of Canada. The Halloween Storm as we called it. Towns all over New England “rescheduled Halloween” by several nights for the kiddees. I spent 3 days without power, while using the gas rangetop to heat the house best it could, and cut-up tree limbs with my chainsaw for 2 days.
    Now I live in Tucson Arizona. Never another snowstorm-snowblower-snow shovel again for me. Ever.
    Global cooling has the potential to be far more catastrophic on mankind and our grain food supplies, than any green-up enhancing warm-up from adding some more trace gas to the atmosphere.
    A major Cooldown for the next 5-30 years is likely coming. That is more likely than any CO2 attributable AGW. And our dishonest US Federal government, taken over by watermelons and eco-fascists, is too corrupted by a “renewable energy” agenda to admit what needs to be done and warn Americans to prepare.

  9. The first trees to change in New England are the swamp maples, down in the low places. I used to think it was because because the cold air settled down in the low places. However I have lived through a few wonderful Septembers where it seems summer will never end. It made no difference to the swamp maples. I am starting to think they wear wrist watches. (They do have limbs, after all.) They just know when the days are getting nearly as short as the nights. Even if the weather is downright hot they start to change around September 10-15, and are at their most brilliant around September 30.
    A light frost doesn’t seem to bother them, early in September. However a prolonged cool period does seem to make there be less crimson at first, and instead they take on the peculiar purple hue that plants adopt under duress. (Apparently plants have a strange ability to function at cold temperatures by minimizing chlorophyll. If you put out your tomatoes too early in the spring, their leaves turn purple.)
    An unusually harsh and early freeze (as occurred after Pinatubo) doesn’t hurry the swamp maples. It just browns the leaves around the edges, and makes them less brilliant.
    The summer here in New Hampshire has been cool and wet. Thermometers make us look warm, as nighttime lows haven’t been as low, but my garden has seen a lot more rot than usual, due to cool and moist days. The swamp maple leaves have a lot of the purple color. That won’t keep them from turning crimson a week from now, but I’m noting the purple down as a sort of indicator.
    The old-timers always said a wet summer led to the most beautiful fall foliage. This will be the year to test out that theory. Cillecting that data must wait, as the sugar maples don’t get going until October (unless they are injured.)
    However my own experience is that trees are not very good thermometers, and are better when used as rain gauges. This involves fall foliage, and the tree ring circus as well.

    • Caleb
      September 18, 2014 at 10:31 pm
      The first trees to change in New England are the swamp maples, down in the low places. I used to think it was because because the cold air settled down in the low places.

      Here in a frost hollow I can attest that this is the case — at least here. I can look up right now & see sugar maples down low & on my bottomland lot beginning to change w/others a few hundred feet up the nearby ridge still solid green. Happens every year.

      • You can also see the effect of temperature by driving north, and seeing the foliage become increasingly glorious (or else, later on, increasing “past peak.”)
        However the other thing I noticed, (about individual trees turning at the same time irregardless of temperature), needs to be investigated further. It was driven home to me because my wedding anniversary is in late September, and my wife and I like to drive to a place where we first got mushy, and I couldn’t help notice the trees were always at the same stage, irregardless of whether the autumn had been warm or cold. (A strong nor’easter or hurricane can make a difference, however.)
        If you are able to live in “Frost Hollow” for a period of years, you might keep a record of when individual trees change, to test whether or not my theory is true, or is sheer bull.
        Also amble out in the brisk and invigorating air and check out the maples that are turning and the maples that haven’t turned. Make sure they actually are all sugar maples, and not swamp maples down low and sugar maples up high.
        The old-timers around here used to scorn botanists, who insisted there was only one species of swamp maple. It didn’t even matter if the botanists pointed out the two trees had sprung from seeds from the same parent; the tree growing in the wetland was a “swamp maple” and the tree growing on the hillside was a “red maple.” The old-timer would point out many differences between the two trees, involving when they budded out, the size of leaves, X, Y, Z, and when their foliage turned in the fall, but what was most important to those old-timers was the density, grain, flexibility and strength of the wood. No matter what botanists say about those cantankerous old geezers, they sure did know their wood. And they used wood from the tree from the swamp for some things, and wood from the tree on the hillside for other things.
        All in all, I’d say science has more to learn about trees. Money ought be spent on that, rather than on adjusting temperatures.

    • Must have been the spring of ’63 or ’64, I tapped several trees around and in the swamp near our house, and got a few gallons of sap to reduce to maple syrup. This was in Mass., North Shore area. There used to be the Deerskin Trading Post in Danvers on Rt.1 that sold maple syrup candy, pure sugar, nirvana to a child.

      • At my farm-based child-care, boiling down maple sap to make sugar-in-snow has got to be the favorite thing we do. To a modern, video-game oriented five-year-old it is sheer magic. (And few people know maple syrup is best when fresh, and loses its taste with time.)
        Old-timers made sugar of other saps as well. Swamp maple makes sugar that isn’t as good. I have heard black birch and sycamore can make sugar, but haven’t tried it. Black cherry sap boiled down to cough syrup, but I never tried that either. Some said this “cure” made you “behave rudely”, however they may have allowed the syrup to ferment and become a concoction that contained alcohol.

      • Hi Steve,
        I was going to take my wife back to Boston and New Hampshire for our anniversary and wanted to get her another leather coat at the Deerskin trading post. From your comment it looks like they closed, or did they move? I could not find them on the internet. My direct email is geservice@hotmail.com Thank you in advance for a reply! Eddie

  10. So trees (and likely all annuals) will have a longer growing season. Because this is coming from alarmists I’m guessing there’s a problem only government can solve through law by executive fiat. So what is that problem?

    • No, that was due to extending daylight saving time, ostensibly to fight Global Warming.
      /sarc (just in case)

  11. But surely the increasing number and severity of storms will have blown all the leaves off by then?

  12. It is of my opinion that the above cited story/report authored by Wendy Plump for the Princeton Environmental Institute is little more than half-truth “weazelwording” apparently for the purpose of renewed Grant funding and/or furthering the fear mongering agenda.
    Technically, the leaves of deciduous trees and shrubs do not change “colors” in the Fall, …. because it is actually a process of eliminating the dominant “color(s)” that produces the “pretty” fall foliage.
    The green chlorophyll is the dominant color during the growing season and when it is destroyed as a result of a normal “shutdown” or an early frost/freeze the next dominant color (sugar) becomes visible to the viewer. The per se “brightness” of said leaves is determined by the amount of “colored” sugars that remain in the leaves after the abscission layer has formed.
    For further reading, to wit:
    Excerpted from: The Science of Color in Autumn Leaves
    http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html
    Many think that cool weather or frost cause the leaves to change color. While temperature may dictate the color and its intensity, it is only one of many environmental factors that play a part in painting deciduous woodlands in glorious fall colors.
    [snip]
    The process that starts the cascade of events that result in fall color is actually a growth process. In late summer or early autumn, the days begin to get shorter, and nights are longer. Like most plants, deciduous trees and shrubs are rather sensitive to length of the dark period each day. When nights reach a threshold value and are long enough, the cells near the juncture of the leaf and the stem divide rapidly, but they do not expand. This abscission layer is a corky layer of cells that slowly begins to block transport of materials such as carbohydrates from the leaf to the branch. It also blocks the flow of minerals from the roots into the leaves. Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal.

    ——————–
    Iffen you want a longer growing season ….. then your best chances for achieving that would be to increase the earth’s “wobble” on its axis ….. thus “pushing” the Autumnal equinox up to mid-October.

  13. Let me give this sort of thing a try:
    Climate researchers today announced the results of their 35 year study on climate.
    “The climate has been higher these last 35 years, except where it’s been lower,” said Pilt Down, government climate researcher. “We found absolutely definitive evidence that human activity, and ONLY human activity, has created thermometers. Prior to human activity there was no accurate way to measure temperature.”
    “This is ridiculous,” cried Dr. Munn, Nobel Laureate from Pennsylvania. “There is absolutely no evidence that humans were involved. Trees, for example, make excellent proxies.” Dr. Munn is currently sitting alone at a table in the back of the climate research cafeteria. The other researchers never quite seem to meet his eyes.
    Meanwhile, no matter what the past, we can see from the study that there is absolutely no doubt about it. With 100% certainty the climate will be higher, except where it will be lower. Beware of wetter and drier areas, some may become hazardous. Storms will be worse, sometimes, and other times will be better. CO2 is the cause of all climate, except that climate is stable while CO2 levels change. Climate is implicated in 14 different types of mental illnesses, causes houses built on flood plains to be washed away, fills dams during droughts, and empties dams during floods. Beware.
    You have been warned. It’s worse than we thought. We HAVE to do something about it, think about the children! Failing to act on this emergency by sending money and allowing us to remove all of your personal freedoms will result in the horrifying specter of a microscopic temperature change in 100 years, and we don’t want to leave that to our great grandchildren, do we? DO WE? Well of course we don’t.

  14. Ok, purely anecdotal, but still scientific. My wife bought a pomegranate tree. Where we live they are not native, so we must pull them inside (I build a greenhouse from plans I found on the Internet – it is a temporary structure). EVERY year, it sheds it leaves at the same time. Even the year we have very MILD falls (this is now an 8 year old tree – and my greenhouse is getting small for it).
    Some trees may do it because of the cold. But around here, most leaves seem to do it because of the amount of sun it gets each day. They are PROGRAMMED that way. The only varying factor appears to be rain fall. In dry years, they shed them earlier – to preserve moisture. But none of my trees shed them faster or slower due to how warm the fall is.

    • You are correct. It is a matter of genetic code which these would-be scientists pretend does not matter. For example, in the mild climes of south Texas the trees start budding around March 1 or a few days earlier. The elms are first, then oaks and the rest. By the middle of March there is full foliage on all of the species except for the pecan, which never buds until tthe second week of April, over a month after the other species. So easy to expose these would-be scientists. I have trouble crediting stupidity to these types but I cannot prove that they are frauds who really know better.

      • It does appear to be genetic. This past year was of course a bitterly cold one until late April around here. We had April snows. But that tree? Started leafing in early March! The days were longer, but the temperatures were still freezing. (and the temporary green house merely keeps things from freezing, it is not a hot house).

  15. If, as we are told, global temperatures have been flat for15 years, how is the leaf coloration index to be calbrated at global scale? Does this limit the potential use of the observations to scenic, but basically useless?

  16. I like this quote,
    “What these results are suggesting is that different locations will change in different ways, and that these differences are actually going to be quite interesting.”.
    Is this to imply that about 100 years ago different locations did not change in different ways, and were less interesting?

  17. I find it difficult to imagine how one performs a separation of the 2 variables, changing duration of day from changing temps as the season progresses using data from just two locations. Locations which are at markedly different latitudes.

  18. A lot of leaves fell early in Calgary but that was mainly because they were still attached to the trees that collapsed under the weight of the snow.

  19. We have had early color here in the front Range of Colorado this year – the earliest I can remember. 1st leaves started popping in the last week in August & we have 1/4-1/3 of trees in peak color today

  20. “Climate change could postpone fall leaf peeping in some areas of the United States as summer temperatures linger later into the year, Princeton University researchers report in the journal Global Ecology and Biogeography. For instance, the paper birch — a popular foliage tree that is the state tree of New Hampshire — could change color one to three weeks later by the end of the century, the researchers found.”
    So, how could temperature have caused it when there has not been any significant Globull Warming for almost two decades?
    “What we noticed from observations was that some trees were keeping their leaves later in the autumn,” Medvigy said. “We tried to make predictions of these phenomena with our models a few years ago, but the results were disappointing. These interesting phenomena have been going on and we had no way of explaining them.” (and of course he still doesn’t)
    So, he will stop making predictions (which would falsify the hypothesis) and just note that things happen and Globull Warming must be the cause.
    Therefore fling more cash so that he can wander through the autumnal forests.
    I am so tired of this B S.
    We’ve lost at least a generation of Scientists who do not know what science is.

  21. I’m not an arborist, nor an actor pretending to be an arborist, but my personal observations of trees has always lead me to conclude that the “turning of the leaves” has more to do with the decrease in sunlight than the ambient temperature.
    For instance, my poplar trees begin to drop their leaves in July, just after peak sunlight, starting with the oldest branches at the bottom of the tree, progressing upward until all the leaves are gone by the end of October.

    • Neo, exactly right.
      From the dept of agric. http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html
      “Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal.”
      What technical training do these author’s have. Here in Ottawa, Ontario, we have a sizable tourist season attached to fall colours and they already know the dates well in advance! Shameful sub- high school science.

    • yes I learned that in first year university Biology class. Auxins are the plant hormones that are stimulated by shorter daylight, this increase in auxins causes the leaves to change colour.

      • The first auxins studied (by Charles Darwin and his son) are destroyed by light and trigger growth in plant tips. They are the basis of phototropism. they’re also involved in the apical grow of pine trees and slow the development of lateral buds, so they keep the tip of the tree in the clear and help produce the proper shape of the tree. They’re active throughout the growth season.

    • And the true cost of the FEAR of Potential Future Global Warming is 4 trillion per year times 100 years.
      25,000 lives killed by your needless fear of the benefits of of a practical, efficient energy system last year in the UK alone. 6 years of recession increased by Obama’s CAGW-spewing economy.

  22. This paper is an example of the decadence of climate science. It is an utterly pointless and worthless waste of resources. It doesn’t pass the ‘so what’ test.

  23. Not only do they change the same time each year by locality, but its not the warmth that keeps the coloured leaves on the tree. These leaves have had it and we can rely on a fall windy day or two to blow most of them away.

  24. Since the Earth is not warming, I guess the Fall colors will occur at its usual schedule or perhaps earlier if temperatures continue to decline!

  25. This idea makes no sense.
    The idea of climate change has been that the largest impact will be in high latitudes (the Arctic). The further north you go, the greater the impact. You would expect that frosts would happen later, while a warmer climate, such as Georgia (or Florida), wouldn’t see much of a change. I guess logical consistency is not very important for the warmist true believer.

  26. I agree with Mr. Cogar post above. Back in the 60’s when I attend college to get a degree in forestry, we studied Photo Period. Each tree has it own time period. If the temps don’t dip below normal for the tree, then when daylight starts getting less, the tree will start the process of losing it’s leaves. This can be seen in aspen tree clones on a hill side. Where some clones will start the fall colors before other nearby clones.
    The idea that warmer temps will cause trees to change their “Photo Period” is possible over many centuries due to them adapting the longer warmer days, but not in the few years they are talking about

  27. Hey, just use the University of Sheffield forecast approach using such a wide range that it captures all extremes in the prediction window.

  28. Chrysanthemums, sometimes called mums, are beautiful “fall blooming” flowers …. and if one is “growing” them in a flower pot, a flower bed or their garden … they can “trick” them into blooming early by what is commonly called “forcing”.
    All one has to do is to “cover” them up like 4 or 5 minutes earlier at the end of each day, starting like 2 or 3 weeks before one wants them to “bloom”. Now I just guessed at those “times” so iffen you want to try it you best read up on it.
    But anyway, said “cover up” simulates a decrease in daylight “hours” which “triggers” the blooming process. Some commercial growers do the aforesaid so that they can get their “potted” plants out to the retailers (supermarkets, nurseries, etc) before their competition does ……. because they know that most customers prefer and/or will only purchase a “potted” plant that is in “full bloom”.

  29. It’s that time of year again.
    ….”No pen can describe the turning of the leaves—the insurrection of the tree-people against the waning year. A little maple began it, flaming blood-red of a sudden where he stood against the dark green of a pine belt. Next morning there was an answering signal from the swamp where the sumacs grow. Three days later the hill-sides as far as the eye could range were afire, and the roads paved, with crimson and gold. Then a wet wind blew, and ruined all the uniforms of that gorgeous army; and the oaks, who had held themselves in reserve, buckled on their dull and bronzed cuirasses and stood it out stiffly to the last blown leaf, till nothing remained but pencil shading of bare boughs, and one could see into the most private heart of the woods.”…..
    Kipling

    • Kipling did live in New England for a while. As I recall, he liked the landscape, but not the people.
      People come from all over the world to look at our leaves. It is quite a sight to see an enormous bus, more glass than chrome, come swaying and lurching down a narrow country lane, filled with gawking Asians and their cameras. I do my best to look picturesque as they pass.

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