A new but unbelievable climate proxy – plant leaf wax

From the UNIVERSITY OF BIRMINGHAM and the “thinnest of evidence” department comes this claim.

Fossilised plant leaf wax provides new tool for understanding ancient climates

New research, published in Scientific Reports, has outlined a new methodology for estimating ancient atmospheric water content based on fossil plant leaf waxes.

As the Earth’s surface and atmosphere warm, the amount of moisture – water vapour – in the atmosphere will increase. Understanding the size of this increase is important for predicting future climates as water vapour is a significant greenhouse gas. Atmospheric moisture content also influences the patterns and intensity of rainfall events.

The relationship between temperature and moisture content can be explored by the study of intervals in Earth’s history when climates where significantly warmer than those seen in modern times, which necessitates a method for estimating ancient atmospheric moisture content.

Dr Yvette Eley, from the University of Birmingham, explained,

“If we want to understand how the Earth would work with a climate substantially warmer than today, we have to study intervals millions of years in the past – made difficult because these warm climates are much older than our oldest climate records from Antarctic ice cores (less than one million years old).”

To try and understand climate properties related to the atmosphere – like rainfall and atmospheric moisture content – in such ancient times is very challenging. Existing methods, using calcium carbonate concretions that form in soils, or the chemistry of fossilised mammal teeth, are both hampered by their relative rarity in ancient sediments.

Dr Eley added,

“Our new approach to quantifying ancient atmospheric moisture content relies on the fundamental properties of plant leaves, and how they alter their protective waxy coverings in response to water stress. These leaf waxes are tough and resistant, and are regularly found as what we call biomarker compounds in ancient river, lake and even marine sediments.”

A method of estimating ancient moisture content based on these plant wax compounds overcomes the limitations of other methods because plant waxes are commonly found in soils and sediments stretching back tens or even hundreds of millions of years and across many environments.

This is the Calatayud-Daroca Basin in Central Spain. CREDIT Michael Hren

The validity of this new tool was proven in studies of modern soils across the US and Central America, carried out by the research team of Associate Professor Michael Hren in the Center for Integrative Geosciences at the University of Connecticut. These studies showed a clear relationship between the chemistry of these waxy compounds and the amount of moisture in the atmosphere.

“What we see is that the distribution of organic compounds preserved in soils seems to be strongly related to the difference between how much water is in an air mass, and how much the air mass can hold, or what is known as the vapour pressure deficit,” says Dr Hren.

Eley and Hren then applied their new proxy to reconstruct atmospheric moisture content in Central Spain during an interval 15 to 17 million years ago.

Although consistently much warmer than pre-industrial conditions, this interval marks one of the cooling steps that led to the development of the modern world. The new data confirms the expectations of climate models, that atmospheric cooling is coupled to less atmospheric moisture. The reconstructed changes in atmospheric moisture also align with results from other independent proxies used to investigate changes in temperature and rainfall in the region.

Dr Eley said, “This gives us the confidence that our proxy works, and we have every reason to believe that it will do so for future exploration into the even deeper past. We hope the results of this exploration will provide direct data to test our understanding of the relationship between global warming, atmospheric moisture content and rainfall systems.”


The paper: Reconstructing vapor pressure deficit from leaf wax lipid molecular distributions

Estimates of atmospheric moisture are critical for understanding the links and feedbacks between atmospheric CO2 and global climate. At present, there are few quantitative moisture proxies that are applicable to deep time. We present a new proxy for atmospheric moisture derived from modern climate and leaf biomarker data from North and Central America. Plants have a direct genetic pathway to regulate the production of lipids in response to osmotic stress, which is manifested in a change in the distribution of simple aliphatic lipids such as n-alkanes. The Average Chain Length (ACL) of these lipids is therefore statistically related to mean annual vapor pressure deficit (VPDav), enabling quantitative reconstruction of VPD from sedimentary n-alkanes. We apply this transfer function to the Armantes section of the Calatayud-Daroca Basin in Central Spain, that spans the Middle Miocene Climatic Optimum (MMCO) and the Middle Miocene Climate Transition (MMCT). Reconstructed VPDav rises from 0.13 to 0.92 kPa between 16.5 and 12.4 Ma, indicating a substantial drying through the MMCT. These data are consistent with fossil assemblages and mammalian stable isotope data, highlighting the utility of this new organic molecular tool for quantifying hydrologic variability over geologic timescales.

Open access here: https://www.nature.com/articles/s41598-018-21959-w


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Patrick J Wood

How about the relationship to global cooling?


“The new data confirms the expectations of climate models, that atmospheric cooling is coupled to less atmospheric moisture.”
These geniuses have discovered the Clausius–Clapeyron effect. Truly Amazing discovery that cooling leads to less atmospheric moisture. Send them more grant money.


“…confirms the expectations of climate models…”
Which confirms my expectations of climate alarmist sleight of tongue ; )

John harmsworth

I have performed the definitive study on this! I stopped cleaning the wax out of my ears and after a few days, it rained! After probing my ear too deeply I then became a vegetable! Ergo…I am a plant and the thickness of my earwax correlates to humidity.
Where’s my grant?


They all keep repeating that no one knows enough to predict climate….

Thomas Homer

“water vapour is a significant greenhouse gas”
I’ve seen CO2 described as an ‘important’ Greenhouse Gas, now we have water vapor described as a ‘significant’ greenhouse gas.
The complete inability to quantify the ‘greenhouse gas’ property in any meaningful way is quite telling.

Thomas Homer

comment image

Thomas Homer

From that Water in Air chart, and knowing the temperature ranges on Earth, it can be derived that water vapor has an effect exactly opposite from the purported ‘greenhouse gas’ property. From either extreme, water vapor drives the temperature back into the Earth’s temperature ranges.

Steve Keohane

Don’t have a source at hand, but recollect 95% of the alleged ‘greenhouse’ effect is water vapor, the rest gasses, with CO2 about half of that 5%.

Neil Jordan

“water vapour is a significant greenhouse gas”
First time I have read this from ClimSci. This might be the first finger pried from the death grip around “carbon”. Changing to another greenhouse gas might keep the gravy train on the rails a while longer. And there’s always that alleged CO2-water vapor positive feedback lifeboat if the train derails.

Thomas H wrote:
“I’ve seen CO2 described as an ‘important’ Greenhouse Gas, now we have water vapor described as a ‘significant’ greenhouse gas.
The complete inability to quantify the ‘greenhouse gas’ property in any meaningful way is quite telling.”
Ponder, ponder, ponder – how to address this very good question, especially for the younger generation.
OK – I’ve got it!
Water Vapour is like, an effing-huge, i mean, totally gigantic greenhouse gas.
CO2 is like, an effing-tiny, I mean, totally insignificant greenhouse gas.
Close enough! 🙂

John harmsworth

Totally awesome, bro’! Kudos! Rock on!

Dude, I unintentionally omitted “y’know” and should have doubled-up or trebled-up on “like”.
Apologies for my lack of expertise in the dialect of the modern snowflake (like, I mean, totally, y’know).

Steve Fraser


Robert Morrow

This study just in: trace amounts of earwax on the index fingertips of climate scientists prove to be an excellent inverse proxy for adherence to the scientific method.


You beat ,e to it. Now, leaf me alone!


me, not ,e

e was always a bit slow.


Fire up the climate change proxy algorithm. It would be more efficient.


I have an indoor garden of coffee trees and mulberry bushes. Wax not only varies per plant, but on individual leaves on the same tree. New leaves are generally very waxy and they lose their luster as they age and eventually fall off and are replaced by new leaves.
They are saying that the wax on leaves is only dependent on water stress and the amount never varies from when the leaf unfurls to after it dries up falls on the ground and is buried in the soil? And that the lipid chain is the same and never altered in any process from when the wax appears to being lithified? I’m just a little skeptical.


I am far more than merely skeptical. There seems to be no explanation on how the data is collected, or from how many sources.
I would really like to see more rigor before this gets any attention.
It’s simply not credible.


Never mind, I answered my own question regarding sampling, looks like they sampled along the Mississippi and along the Appalachians. But after reading the paper I am less than assuaged.

Bryan A

Must have written the report on Wax Paper


Hi RWturner, – I assume researchers were studying “wax” that originally was polymerized inside (“intra-“) the leaf cuticle layer & not the “wax” that originally was more soluble in the surface (“epi-“) leaf cuticle layer. My point being that not every kind of leaf “wax” is still around to be tested due to different susceptibilty to degradation of surface (“epi-“) “wax” (which is distinct from the aging leaf “wax” lipid per-oxid-ation).
As a grower you may like Jetter & Scaffer’s (2001) “Chemical composition: Prunus laurocerasus leaf structure. Dynamic changes in the epicuticular wax film during leaf development”. If time pressured 1st skip to text’s “Discussion” section as they cover several aspects you’d probably like. Free full text available on-line (doi.org/10.1104/pp.126.4.1725); maybe try link = http://www.plantphysiol.org/content/126/4/1725

Meaning that leaf wax teams are allegedly capable of estimating atmospheric water content; for one leaf, on one plant, at the leaf’s relative position above ground.
All micro-climate.


Water vapor may be safe for the moment…I’ve been hearing (gov employed) alarmists say methane is the new CO2. Nat Geo said the dinos dunnit:

John harmsworth

Crap science! Literally!


I’m not understanding exactly how they are estimating the amount of wax on these ancient leaves.

D. J. Hawkins

It’s not the amount of wax. It’s the chain structure of the lipids.


it’s a proxy for a proxy. Lets extend the speculative chain to realize that they are using secondary analyses to determine the proxy of the proxy of the proxy.
How many layers deep before the lunacy is realized?

@ rocketscientist…that would make a great study “…How many layers deep before the lunacy is realized?…”.


What are the chances of these lipids surviving 11 to 13 million years so that they can be sampled?


That is the main issue I have with this, without having taken the time to study the paper. It seems to me that the burial conditions of the leaves would be more important than slight changes in the original composition of the leaves.


I easily buy that you can use such proxy for a crude assessment of whether the plant leaf suffered water stress … when it died.
I don’t buy any VPDav figure. This just seem another case of
“the inaccuracy of the proxy is balanced by the number of decimals”

The validity of this new tool was proven in studies of modern soils across the US and Central America
Over what period of time? One year? Ten years? 30 years?
This is exactly how the tree ring circus started. They found a correlation over a few decades, screamed “hurray! we have discovered treemometers!” Then from 1950 on, the treemometers diverged from the temperature record. Which lead to Mike’s Nature Trick and Hide the Decline. When those were unmasked as the fr**ds they were, the story changed to “yeah, well, so treemometers aren’t accurate for the last 60 or 70 years, but we have no reason to believe they weren’t accurate for the 2,000 years before that”.

Old Man Winter

Like you, I’m Old School: “Fool me once, shame on you.
Fool me twice, shame on me.” Since ClimateGate and the
Mannchild’s tree ring circus ;), unfortunately there
ALWAYS HAS to be a question mark about anything supporting
The Team’s propaganda. I’d like to see Steve MacIntyre’s
opinion on this proxy as he has done yeoman’s service for
us to get a better understanding of proxies, especially
about ALL the factors that affect the limitations &
veracity of the proxy, as we are often misled about
such information. It could lead to a healthy debate
among those more knowledgeable of proxies rather than
having the rest of us speculate as to what those factors
and limitations might be.


Hey. Paleobotanists need to eat too. They deserve a piece of the Global Warming government complex funding gravy train too! Don’t they?!



Ha Ha, they just debunked their own CAGW narrative.

As the Earth’s surface and atmosphere warm, the amount of moisture – water vapour – in the atmosphere will increase.

There goes the increased drought meme.

…intervals in Earth’s history when climates where significantly warmer than those seen in modern times.

There goes the unusual and catastrophic meme.

John harmsworth

Not to mention that they show no awareness of any limiting factor to this upward “death spiral” Surely the planet would have run away to million degree temperatures by now. They don’t even have the brains to see the inherent nonsense of their premise!

“As the Earth’s surface and atmosphere warm”
This is a ritual and mandatory benediction at the start of a climate paper, the equivalent to the Is1amic
“Bismillahir Rahmaanir Rahim” (In the Name of A11ah, the Most Merciful, the Most Compassionate).


Sorry – off topic but is anyone else having trouble connecting to Jo Nova’s web site – I get sent to a “Mediacom” welcome page – even if I use the link in thise website or search for it on Google


Just tried the link on the right bar for you…went right to Jo’s for me

If your on Windows open a command window (have to run as administrator) and type ipconfig /flushdns

Bruce Cobb

“If we want to understand how the Earth would work with a climate substantially warmer than today,…” blah-bla, blah-bla, blah. Warmology 101: always start with the assumption that the Earth will be “substantially” warmer in the future (unless we do something drastic now). After that, everything is just window dressing. Plant waxes, yeah, whatevs.

Mark - Helsinki

What utter nonsense!!!!!!
This is the most ridiculous thing I have head this year and THAT is saying something!!!




And, it is still early in the year.


Leaf-Wax alkanes are very chemically stable, and have been studied as proxies quite a bit. For example the Deuterium/Hydrogen ratios and d13C carbon isotope ratios as proxies for the composition of rainwater and the isotopic makeup of atmospheric CO2. It seems to work in a way, but there are problems:
1. Leaf Wax being very stable gets transported quite a bit. Leaf wax alkanes in sediments can come from plants that grew thousands of kilometers away.
2. Leaf wax is only synthesized during a few weeks when the leaves flush, and only reflects environmental conditions during this short interval in spring/early rainy season.
3. Different plants growing under similar conditions apparently have different ACL (Average Chain Length)
Another interesting fact. ACL (Average Chain Length) of Leaf waxes has actually been used as an environmental proxy since the 1970’s. However not as an indicator of water stress, but as an indicator of the ratio of woody/non woody plants. However this apparently doesn’t work consistently:
So, leaf-wax ACL is probably a proxy of sorts, but it is rather uncertain just what it is a proxy for, where the proxy applies as well as when.


Oh Dear! I do wish these scientists would do their homework before launching into research programs such as this.
If they wanted to know how the humidity levels and water quantity in the atmosphere altered with temperature; then all they needed to do was to refer to the Steam Tables. The information is all there.
Earlier, in my rough way I calculated that based on IPCC figures an increase to 600ppm in CO2 levels would increase atmospheric water content by about 0.036%. Not quite temperature related and with the envelope used for the calcs. now dumped; best not take this as valid. However the calculations can be done and indeed better by better brains than I.
Can’t be bothered to repeat the excercise myself.
However it should be noted that when you turn up the heat on your kettle the water merely boils faster; but the temperature remains the same. Also in the Rankine Cycle the quantity of the working fluid remains constant. (leakage ignored). The atmospheric Hydro system being a Rankine Cycle which cools the earth as a thermostat; so the Steam Tables can tell us much.
On another aspect: Their homework should also include mugging up on Chaos Theory, where they would realise that past stable conditions in a chaotic system cannot be transposed to a future situation.

John harmsworth

Exactly Alasdair.
I find there are lots of people on this site who have a solid understanding of physics and engineering factors which relate to atmospherics. One wonders what the “hard science” background and abilities are for many of the activist pseudo climate scientists and biologists who delve come at the climate issue from extreme tangents. I guess they can figure where the money is.


“As the Earth’s surface and atmosphere warm, the amount of moisture – water vapour – in the atmosphere will increase.”
Except that it hasn’t at least since 1948. See climate4you, climate and clouds for the data.


There have been a number of changes in ocean circulation over the last 13 million years. This can have a big impact on humidity levels in areas near the coast.

Caligula Jones

Numberwatch has a great list of things caused by global warming:
I guess we now need a list of measures of global warming…
Although this one SEEMS to be the dumbest, I don’t think its even close compared to bee tongues:

The leaf wax palaeo is not new.
But it’s a perfectly good proxy, waxes are durable and leave a long record of density of leaves blown out to sea (inverse of aridity) – what’s not to like?
Jessica Tierney of the University of Arizona, USA, reconstructed climate at the “Horn of Africa” – the region including Ethiopia and Somalia at the south of the Red Sea – from cores of sediment from the Arabian Sea, using chemical traces of the wax from leaves blown out to sea in the sea-floor sediments, allowing them to reconstruct which periods over the last 200,000 years were either arid and dry or green and wet.
They discovered – to their surprise – that at the period around 60,000 years ago, when the exodus of modern humans from Africa took place, the Horn of Africa had turned arid and dry. This is puzzling – it would have made the Odyssey from Africa more challenging – but evidently it didn’t stop it from happening.


However they used another and much less dubious proxy: the deuterium/hydrogen ratio of the waxes which mirrors the isotope ratio in precipitation, which in turn indicates qualitatively the amount of precipitation (N. B. this only applies in the Tropics).
By the way the linkage to “out of Africa” is very dubious. There is absolutely no evidence that this migration went by way of the Horn of Africa rather than along the Mediterranean coast. Indeed it is unlikely since there is no evidence for seafaring that early.

Thanks for the proxy clarification.
The route out of Africa is not the point here.
There are only so many land routes from Africa to Asia.
It’s about aridity around 60 kya, the time of the migration from Africa to which most humans today trace their ancestry.
Yes there were dozens of other exodi from Africa (yawn) before and after, that’s not the point, the genetics (e.g. mitochondrial haplotype L3) is incontrovertible that the 60 kya event is ancenstral to today’s population, the others only contribute a tiny fraction.

John harmsworth

In the study of human origins there is one constant. Whatever someone has recently dug up represents the oldest, most important, game changing, species first and mind blowing discovery, EVER! Until the next one. Modern ? humans were in the Middle East 200,000 years ago. Whatever Neanderthals evolved from was probably in Europe perhaps 400,000 years before that. Denisovans is still a question mark and the Chinese have totally different ideas about their specific evolution. This book is being re-written too regularly to say much definitive about the exodus from Africa.

Yes there were dozens of other exodi from Africa before and after, that’s not the point, the genetics (e.g. mitochondrial haplotype L3) is incontrovertible that the 60 kya event is ancenstral to today’s population, the others only contribute a tiny fraction.


I’d like to see what their proof is that the leaf wax variations must be showing variations in temperature rather than some other stressor on the plant such as drought. Seems like it would have the same problems that tree rings have when used as a temperature proxy.

It is being proposed as a proxy of wet or dry – verdant or arid.
How much water in the air near the coast.
Not temperature.
That’s exactly the point.

John harmsworth

I agree. I believe most plants have specifically evolved leaves to either shed water in rainy environments or conserve it in dry. I would be very surprised if this adaptation is not present on a smaller scale to adapt to the particulars of natural variation. plants have had millions of years to evolve mechanisms to regulate their response to temperature, moisture, light availability, insects, soil nutrient availability and assaults from herbivores. The notion that the leaf wax would be solely dependent on temperature is ridiculous to me. Where are the sextuple blind experiments?


Not unexpected. As the climate changes it is quite normal for choices of proxies to become crazier and theories to become more pretzel like.

JRF in Pensacola

Well, you folks have pretty much nailed this one down. I will say that it is an interesting paper and I encourage researchers to try and find relationships that may shed light on different physical, chemical, biological, geological, etc. processes but I wish the authors would state that: 1) the proxies they use may not have, or do not have, the same accuracy and precision as the targeted measurement and that 2) they assume that the accuracy and precision of the proxy remains constant over the time period in question unless shown otherwise. Frequently, papers of this nature do not mention that more than one variable is important (such as tree rings are only affected by temperature) but this paper does state that only 50% of the variability is accounted for in their statistical analyses. This particular paper generates several such questions regarding the stability of the data over millions of years since “Time Zero” for any particular data point and effect of the sum of environmental variability that ensued. But, again, an interesting offering.

michael hart

It’s just tree rings again, only worse. Pick some supposedly-measurable composite quantity, any one you want, that is dependent on a whole host of other variables, and then assert that is really only dependent on the variable that interests you today.


Some commenters here are unreasonably dismissive of the paper. There is no logical reason why we shouldn’t explore whether the composition of these compounds in sediments could be an effective proxy for humidity, and on the evidence they provide there is at least a prima facie case made that it can.
Whether it will have much bearing on the present climate debate is entirely another matter of course, but I don’t see that being claimed by the paper anyway.
One thing that surprises me is the inherent assumption that the mix of chain lengths found in the wax residues is independent of the plant species- and indeed different phenotypes within the species – in which they were produced. Pretty much everything rests on this. It might be right, and perhaps some work has been done to support it, but to me that’s counter-intuitive.