My Oh Miocene

Guest Post by Willis Eschenbach

It was hot here a couple of days ago. I walked past a huge aloe vera plant, taller than my head, that grows by our house. The heat radiating off of the plant was palpable. I could feel a wash of warm air over me as I stood downwind of it. For a while I thought about the curious ability of plants to heat the air around them, and then I let it go.

Figure 1. Solar absorber, natural style. Note how the design efficiently intercepts sunlight because of the spiral, uneven pattern of the leaves. Also note that the design keeps photons from escaping through the funnel-shaped nature of the leaf pattern. Finally, consider that when the plant emits IR from the inner leaves, it will be re-absorbed by outer leaves, perhaps a number of times. This gives the plant, in effect, a local “greenhouse effect” due to the multiple re-absorption of the IR. The leaf geometry also greatly slows down the passage of the air through the plant, once again increasing the local warming. The net of all of those is a warm plant, surrounded by warm air.

I was reminded of our aloe vera again when a friend sent me a copy of the paper “A Warm Miocene Climate at Low Atmospheric CO2 levels,” by Knorr et al. It reports the results of a climate model analysis of the Miocene, the period from about twenty-three million years ago up to five million years ago. It is in press at GRL (paywalled), but the results are discussed here.

In their abstract, we find (emphasis mine):

In this study we present climate simulations of the Late Miocene (11-7 Ma) with a preindustrial CO2 level, using a coupled atmosphere-ocean general circulation model (AOGCM). The simulated global mean surface temperature of ~17.8 ºC represents a significantly warmer climate than today. We have analyzed the relative importance of tectonic [shape and location of the continents] and  vegetation changes as forcing factors. We find that the strongest temperature increase is due to the Late Miocene vegetation distribution, which is more than three times stronger than the impact induced by tectonic alterations. Furthermore, a combination of both forcing factors results in a global temperature increase which is lower than the sum of the individual forcing effects. Energy balance estimates suggest that reduction in the planetary albedo and a positive water vapor feedback in a warmer atmosphere are the dominating mechanisms to explain the temperature increase. Each of these factors contributes about one half to the global temperature rise of ~3 K. Our results suggest that a much warmer climate during the Late Miocene can be reconciled with CO2 concentrations similar to pre-industrial values.

In looking at the effect of plants on the climate, I’d like to discuss the use of the models, how much weight we should put on their results, and how they could be improved.

The first rule of models says

All Models Are Wrong, But Some Models Are Useful

Their usefulness, of course, depends on their ability to replicate the reality which they are modeling. One issue with the models is that many of them still are not what I call “lifelike”. I discussed this problem of “lifelike” climate model results here. If the models do not act like the real climate, why should we believe them? Unfortunately, no one has ever instituted this kind of test to compare all of the models. It should be a part of a standard suite of climate model tests … dream on.

So at the moment we don’t know if the climate model used in this test gives a lifelike simulation of today, much less of ten million years ago. But I digress. The study says (emphasis mine):

We utilize the comprehensive AOGCM ECHAM5-MPIOM without any flux corrections [e.g. Jungclaus et al., 2006]. The atmosphere model ECHAM5 was used at T31 resolution (~3.75º) with 19 vertical levels. The ocean model MPIOM was run at an average resolution of ~3º with 40 vertical layers. Vegetation is a fixed factor represented by specifying different land surface parameters like albedo, roughness length, vegetation ratio, leaf area index and maximum soil water capacity.

Here we run into another modeling problem. They have set up the vegetation parameters to coincide with what we know of the Miocene landscape. This, of course, means that they are using vegetation as a forcing, rather than a feedback.

But we have been informed, over and over, that the vegetation is a feedback and never a forcing …

This is both a strength and a weakness of the models. We can make assumptions like where the vegetation grew and force things in the model to be a certain way. Then we can see what the effect of that on the results might be.

Unfortunately, the climate doesn’t work that way, where one thing holds steady while everything else changes. So even though we can get some insights, we have no assurance that the effect that we find is real. For example, we don’t know if the Miocene vegetation (which is specified) fits with what the model says were the climate patterns of that time.

Setting aside the manifold questions about the model, there were a couple of interesting parts of the study. The first was that they find that the main effect of the plants occurred through a change in the albedo, particularly for the Sahara. This is in accord with my experience of the aloe vera plant, where it was absorbing much more energy than the ground around it. In part this was because of the albedo of the plant being lower than the ground beneath, but in part it was from the geometry of the plant. (This latter effect is neglected in the model.)

The second interesting thing involves these two statements of theirs about the albedo:

The planetary albedo in MIO [the Miocene simulation] is reduced by ~0.014, which causes less shortwave reflection by the atmosphere and a warming.


Based on a zero-dimensional energy balance model [e.g. Budyko, 1969] the impact of α [albedo] and ε [effective long wave emissivity] can be quantified, each causing about one half of the global warming of ~3 K.

Assuming the same solar intensity as the present (345 W/m2), which the authors say that they have done, this change in albedo would result in a change in solar radiation of 0.014 times 345 = 4.83 W/m2. Given the temperature change of 1.5°C from the albedo change, this gives a climate sensitivity of:

1.5°C * 3.7 W m-2 per doubling_CO2 / 4.83 W m-2 = 1.15°C per doubling of CO2.

Me, I think that climate sensitivity is an illusion based on a misunderstanding of how climate works … but for those who believe in it, using Knorr et al’s figures and their concepts, that gives a very low sensitivity, well below the IPCC canonical figure. The IPCC AR4 Summary for Policymakers says (emphasis mine):

The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing. It is not a projection but is defined as the global average surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C.

“Very Unlikely”, in IPCC jargon, means less than 10% chance that the sensitivity is less than their minimum estimate of 1.5°C per doubling of CO2. Despite that, this study shows a sensitivity of about three-quarters of the IPCC minimum estimate …

So you’d think that the media headline from this study would be

“Climate Model Finds Extremely Low Climate Sensitivity”

Sadly, that might happen, but only in an alternate universe …

Best to all,




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The aloe vera plant is an evolved bubble. The canopy is the skin of the northern hemisphere. The trunk is the polar axis while the root system occupies the southern hemisphere. Such is the way that life forms are manifestations of energy forms.

Mike Bromley the Canucklehead

Along with radiative concrete, asphalt, siding and the like, should we now also be recognisant of thermometer placement near plants too? It would seem so. Oh no! The science…unsettling again.

Robert of Ottawa

Models are usful tools to assist thinking about a problem; they are qualitive in nature. No weight shold be given to their quantative outputs.

This “multiple re-absorption of IR” is simply scientific nonsense. Like “positive feedbacks” these are nothing whatsoever with physics, but invented pseudoscientific explanations given by the crooked which have great currency with the gullible.

Doug in Seattle

It must be one of those “When it suits the argument” things.


Does Trenbirth’s “Energy Budget” even include the biosphere? Is his “missing heat” wrapped up in all those living things that get energy from the Sun and then store as matter? After all, the oil and coal we combust is just past energy from the Sun stored as matter millions of years ago.
Just sayin’ …

I haven’t seen empirical evidence of an alternate universe either. 😉


As always – fascinating!!!

Dan Brinkman

Ok, I’ll weigh in here since no one else has. First, I’m up ridiculously early which accounts for the first sentence. Second, he needs some more plants around his deck. Third, I’d hate to have to refinish that deck. Fourth, I hope those windows are north facing, though they look reflective.
Willis, I like your writing. Keep it up.


when you stand downwind of the aloe and feel the warm air –
do you suppose that air was heated by infrared radiation?
when i look at the aloe, i see a very efficient shape for a heat sink, such as is used to conduct heat from a cpu to the air.

Thanks for the article! Indeed the Echam climate model is one of the models with the lowest climate sensitivity. They simulated the MWP-LIA-current climate based on the Esper (in other simulations, they used Moberg) reconstruction (with huge natural variability), with reasonable success, while other climate models use Mann’s reconstruction (with very low natural variability). The difference is that with huge natural variability, there is little room for a huge CO2 effect and reverse. See:
For the Eemian warm period, they used the same model to simulate two periods at the beginning and the end of the warm interval:

Plants convert Sunlight into matter. Ergo they are a cooling feedback not a warming feedback. Personally I have never felt warmer standing next to a plant of any description, regardless of the weather conditions. Always cooler.
Forests and wooded areas are always cooler, because the leaves absorb Sunlight and reflect mostly green SW and therefore provide shade below. Then when the wind blows through the trees it is cooled.
The incoming IR is also used by the plants for energy. The longer the grass on your lawn, the cooler it feels on your bare feet in the hot sun.
The logic of this piece is upside-down. Why do we always measure temperature in the shade?
We don’t “say the temperature in the shade, except the shade of a tree, is . . . . .” do we?
In the hot sun, which is the warmer, bare earth, sand, rock, tarmac and concrete, or grass?
It is a logical fallacy to claim plants are a warming feedback. Plants cool.

Julian Braggins

One thing I can agree with is that albedo is most important in long term climate.
In fact I’m coming to the conclusion that it is the only factor.
The Sun is the source of all our incoming energy.
Albedo rejects a varying amount of this energy.
The remaining energy cannot be increased overall. (or we would have a new energy source)
All the rest down here is climate.
Any variation to the energy budget must be external to the Earth, other than albedo.
As long as there is water, for water vapour, additional GHG’s are irrelevant, as temperatures are reset down each night by radiation.
Mankind can only influence long term changes in the energy budget via albedo.
Punching holes in the above summary is welcome as it will increase my knowledge, and possibly some others.


Is it only Miocene plants that cause this warming? If not, when we burn down the village to save the planet by planting trees, are the trees contributing more to “global warming” than the land did before they were planted?

Philip Bradley

I think they demonstrated that you can tune any sensitivity you like into the models.

John Marshall

Seems like an area for further study.
Send more money. Double the grant.

Eyal Porat

Willis, you had me puzzled this time:
I live in a rather hot place (north of the Sea of Galilee), with max average temp in summer of 36C.
My experience is that vegetation (of all kinds) has a cooling factor. It also causes humidity to rise distinctly.
Where is the truth then?

Well that is a wonderful specimen of an aloe vera plant, Willis. I don’t know how your observations would stand up to scientific inquiry though, not that I am disputing this. However, I can add something. In the New England National Park (NSW) temperate rain forest, there are fire trails driven though it, and this separates the temperate rain forest from adjacent grazing land. Possibly no more than 30 ft maybe 40 ft. But when you step into the rain forest area, the temperature feels warmer and a lot more humid of course. I am not describing a ‘hack your way through Amazon type tropical rain forest, just a temperate and in small areas sub tropical rain forest. The main trees are varied, but there is an abundance of antarctic beeches, that defy becoming deciduous as they would normally but maintain leaves all the year around. They over dominate the eucalypti trees who are forced to grow high to gain foliage, visible to the sun.
Also these type of rain forests defy bush fires more than other forests, particularly ‘gum’ trees that have oils in their leaves, and also have evolved to survive bush fires.
It is a very damp area and actually nearer (and at a lower altitude) the coast (and warmer) the problem is leaches. I went to the ladies’ powder room, at the Dorrigo National Park sky walk (I suffer from vertigo so didn’t go on the sky walk, but you can Google and see it if you like) and a Swedish tourist was in there, and removing leaches from her legs. She had only walked 50 meters into the surrounding sub tropical rain forest. Certainly trees and plants give off vapor and also exude energy. But I don’t think this would add to global warming but certainly surrounding
atmospheric water vapor that would eventually form rain or the likelihood of lower cloud cover.
Certainly removing large tracts of rain forest in the Amazon area, has with a 10 year scientific report (I studied this at University AT UNE ‘Earth in Crisis? Course. It was only a 100 level course, but I wanted to fill in my BA unit requirements and chose this rather than doing another 300 level course) caused the cloud cover to go higher and actually is thought to alter rain fall not only in the area but up to 100 km away from where the trees were felled. They thought that leaving equal tracts of rainforest per the trees cleared helped solve this problem. Not only for wild life, but also compensated for the amount of transpiration given off from the rainforest when lots of trees are cut down.
Interesting hypothesis though, go for it.

anna v

It has been found that trees have mechanism tries to keep temperatures in an optimum range around 21C.
Thus if it is hot they are cooler and if it is cold they are warmer, from the link above:
a recent study using infrared thermal imaging of a mixed forest in Switzerland agreed with the current study: canopy temperature was 4-5 degrees (Celsius) higher than the cool, ambient air temperature of Switzerland.

Unless this is taken into account the whole thing is an exercise in futility, model or not.

> Plants convert Sunlight into matter. Ergo they are a
> cooling feedback not a warming feedback.
Yes, I think this is generally true. I first noticed this years ago while scooting around town on a moped, in Florida, The air temperature around groves of trees felt cooler then air around open lots. Vegetation tends to absorb energy, not scatter it. (We get the energy back when we eat the plants or burn them for warmth).
Aloe vera plants are somewhat unusual in that they they exhibit Crassulacean acid metabolism or “CAM” photosynthesis. So they release CO2 during the day and absorb it at night, opposite of most green plants temperate climates. This allows the plant to conserve its water content (95%) by closing its stomata (pores) during the day when its hottest. This lowers the transpiration of its water content.
So, Willis, at what times during the day or night did you notice this thermal phenomena?

Oh what a tangled web Willis weaves.


The aloe vera plant is most useful for treating small wounds; just cut off a leaf and squeeze some liquid on the damaged skin. Leave it moist, repeat this once again half an hour later. The next morning the wound is closed.
It might be more useful that the present CAGW climate models!


The Aloe is a CAM plant (there are three types of photosynthesis – CAM, C3 & C4). CAM types includes cacti and other succulents. Their stomata are closed in hot sun (they capture CO2 at night). The aloe plant would be hotter than C3 or C4 plants in the same situation because it is not evapotranspiring (because stomata are closed). Normally (in a C3 tree, say) the evapotranspiration would lead to a cooling effect.
So to the model – well it would depend on what kind of photosynthesis was dominant in the Miocene. Not significantly different from now, I think.
By the way, the arrangement of leaves in spirals etc so as not to shade one another is called mosaic.

Ask why is it so?

When short wave radiation is absorbed the energy is converted into usable energy, (in plants energy is used for food/growth) and long wave radiation and unusable energy, heat. Your Aloe Vera plant wasn’t re-absorbing LW radiation it was responding to the initial absorption of SW and producing LW and heat. SW radiation is a constant during daylight hours, it moves at the speed of light, absorption, reflection and re-emission occurs in nanoseconds. Your plant uses what it needs and then expels what it doesn’t want. Re-absorption of LW is extremely unlikely as your plant, by its color and texture, has a predetermined absorption/reflection ratio and absorbing additional LW radiation would probably compromise it. Wondering if your plant is contributing to the temperature, it is, as does everything within the troposphere that can absorb short wave radiation. Yes this does seem like an area for further study. Send me the money. 🙂

The topics of parastichy, the golden angle, the distribution of sunflower seeds and the pyhllotaxis relationship to Fibonacci numbers and so on – these have been the subject of many papers, some very advanced. It is my personal doubt that the shape and distribution of leaves and the relationship to paths of light and heat do not have much to do with anything energetic. Unless the plant can move to follow the Sun (and yes, some flowers can, but this is largely unrelated) I believe that the energy intercepted by the plant as the sun moves from dawn to dusk is about constant. The geometric shape that you note about Aloe vera seems to arise because plants grow to a template, some being more obvious than others. One beautiful template is shown in
Also, is it possible that the life cycle of a typical plant, including decay, is exothermic?

Filbert Cobb

Plant cells are subject to the evaporative cooling effects of transpiration. This allows them to operate within an acceptable temperature range.
Perhaps someone will explain the general effect this would have on atmospheric temperature. I can’t, because I am too thick, and never really understood all that stuff about latent heat of evaporation. Like, where does it go?

Bill Illis

This article is very consistent with my compilation of the data. The Miocene was up to 4.0C warmer than today, had more precipitation, forests grew over almost the entire planet and CO2 levels were mostly below 280 ppm.
The difference is the lower Albedo of the Earth’s surface since it was primarily low-Albedo forests in this period and the only high-Albedo ice in the period was in Antarctica which was probably only a third glaciated at this point (sea ice in the winter of course). About 8 million years, the climate became dryer, a few deserts reappeared, and the C4 grasses started growing in greater abundance (prior to this, grasses were rare having only evolved 24 million years ago and they only start to out-compete C3 plants when there are low CO2 levels and when it is dryer).
What caused the lower Albedo, primarily the location of the continents and the ocean circulation systems. At 25 million years ago, the Antarctic Circumpolar Current was pinched off between Antarctica and South America and the Current stopped. This ended Antarctica’s isolation in an extreme polar climate and caused Antarctica to lose more than half of its ice. The Atlantic Ocean and the Indian Ocean were connected through the Meditteranean-Tethys Sea. The Atlantic and Pacific were connected since the Panama Isthmus hadn’t formed yet.
The long march to the recent ice ages started at 14 million years ago when Antarca started reglaciating and the Current started up again, at 8 million years ago when the climate became dryer and the Meditteranean closed off and at 3 million years ago when ice started building in the northern hemisphere as Greenland drifted far enough north to accumulate continental sized glaciers.
Albedo as an explanation rather than CO2 (these are my estimates, there isn’t really any peer-reviewed ones). Albedo only needs to change by a very small amount to have large impact on temperatures but it also takes a lot of change in the Earth’s surface to move the numbers off 30%, primarily glacial ice build-up.


In the right places, on a sunny windy day you can feel the heat boiling off dark green pines. It takes some distance for the hot air off the pines to mix with the cooler air and you can definitely feel the temperature changes (probably 10 F at times). Since many pine forests were clear cut at the turn of the century, I always thought temperature graphs starting around 1900 in such areas were “logging-biased” in a double-whammy fashion because 1) the intial 1900 temperatures were biased colder (because of bare clearcut ground), and 2) the eventual regrowth of pine would make the area experience a local warming that had nothing to do with anything other than the regrowth of dark pines.

D. Cohen

Healthy Aloe Vera leaves are green. This plant looks very unhealthy. You may have been noting the heat of decay from all its dead and dying leaves.

bob sykes

One thinks of Gaia:
Watson, A. J., and Lovelock, J. E. 1983. “Biological Homeostasis of the Global Environment: the Parable of Daisy World,” Tellus, vol. 35B, no. 4, pp. 284-289.

I think models do have a couple of good uses. One is to teach students about the major factors in a system and how they inter relate and interact, The second is to demolish manifestly ridiculous claims made by the uninitiated (where words just wont do the job).
But anyone who uses them to predict is an idiot imo.

Gail Combs

As usual “It is more complicated than you thought”
So plants will try to alter the environment to cooler or warmer to give themselves the optimum temperature. There is also the “shade is cooler” wet feels warmer in hot weather and cooler in cold weather and the change in the amount of wind under a forest canopy.
Have you checked the temperature next to the Aloe Vera and a short distance away with wet and dry bulb thermometers at different times of day and at different ambient temperatures, Willis? It would be an interesting study.


Julian Braggins – I think fundamentally you are correct. The energy the Earth receives is dictated by the relevant energy output of the Sun and the distance the Earth is from it. How much temperature in the atmosphere is dictated by air pressure and not the composition of the atmosphere as shown here. Everything else is the interaction of energy and the chaotic fluid systems (gaseous and liquid) of the planet and is best described as weather. It is a matter of debate or definition as to wether or not the albedo is really part of the interaction (weather) or part of the energy profile (climate). For me albedo at the top of the atmosphere affects the base energy and is climate whereas albedo at any other point is part of the interaction and is therefore weather.

Scarlet Pumpernickel

Just like to make the point that the plant in the picture is not Aloe Vera. It is an Aloe, Aloe Vera is a different plant which is more like a single head. The above plant is an Aloe, but I’m not sure exactly which one it is. eg there are many species of Aloe, and the pictured one is not Aloe Vera….

G. Karst

Plants DO modify their own micro-climate towards THEIR ideal. In so doing, collectively they modify the macro-climate. When plants inhabit the entire globe, we will have achieved the ideal climate, in respect to food production and temperatures. It would also mean the current ice age has come to a end… finally. A new equilibrium era will have begun, and reshaping familiar coastlines will follow, this homogenization, NATURALLY. How we maintain sufficient CO2 levels to sustain such levels of bio-mass, is another matter.
Hominidae are an important part of this bio-mass. Being a predatory species, we will thrive when our prey thrives. Familiar geographic features are unimportant to this march, and life continues to reorganize. As, since time immemorial, we must still follow the caribou/buffalo herd. GK


the Echam climate model is one of the models with the lowest climate sensitivity

But it seems well within the IPCC range
The climate sensitivity of ECHAM4 is about 2.6ºC. which is different to what Willis is saying

Jeff L

Taking results at face value, the obvious question is how much of global temp change over the last 100 years is due to land use / vegetation changes over the same time period, as this study suggests the effect could be considerable & we know our global landscape has been modified significantly over the same time period. I recall that Pilke Sr has published on this concept.

Alan D McIntire

The dispute over warming versus cooling of plants reminded me of this paper by John Christy.
In the Christy paper, the main effect on temperature was due to IRRIGATION of the California central valley rather than directly due to plants, but I think the main argument holds forplants versus no plants regardless of irrigated or growing naturally. Plants have a lower albedo than the naked ground. This will result in more energy absorbed by the earth and less reflected away. Plants also transpire . The result will be cooler days and somewhat warmer nights, with an overall net warming..


Interesting. Most pines’ use the end-needles on the branch-tips to reflect & focus light on the central terminal bud. I’ve visually noted this on sunny days as the tip-buds light up like candles.

Billy Liar

There’s lots of lift for glider pilots over forests.


Oh, just checked -it should have been echam5 which when I looked it up in AR4 seemed to have a equilibrium climate sensitivity of 3.4 Deg C (that is ECHAM5/MPI-OM – is that right)


The models are doing what they are being used to do show CO2 and temperature going up to provide a purpose for taxes, regulations and red tape to counter the whole thing.


Fascinating article.
Willis, you appear to have made an error in comparing climate sensitivities. The IPCC ranges include water vapor feedback, whereas your 1.15 C estimate is based only on albedo change. Apples and oranges, no? Further: Knorr et al attributed half of the 3K Miocene warming to the water feedback (also clear from the abstract).

My house: Surrounded by 27 major trees. Mostly Red and White OAKS.
Front thermometer, back thermoment (remotes)…and walk out in the street and look at the “official” temperature.
Typically 4 to 8 degrees F LOWER in the summer, (closer to 8 during the “peak of the day”.)
Then 2 to 4 degrees HIGHER during the winter (than the “offical” temps.)
Yes, a little “micro universe” with different conditions than the “macro” world. Cause? Agreeded, during the summer- net absorbtion of incoming SWR. During the winter, “insulation”, damping of outgoing LWR.
Net balance? NO IDEA!

Jim D

They say half is the albedo change and half is the water vapor feedback. This means that the sensitivity including feedback is 2.3 degrees per doubling, not 1.15. I don’t know what Willis is talking about.


Bang goes the Fibonacci Sequence theory for solar panels too-
Damn! Now I’m gunna have to put em all back in nice neat row again.


Truthseeker says:
October 1, 2011 at 6:24 am

Everything else is the interaction of energy and the chaotic fluid systems (gaseous and liquid) of the planet and is best described as weather.

What you say is true (“best described as weather”), but that’s only part of the picture. The liquid portion of the fluid systems you identify, the ocean, is most significant in absorbing energy from the sun, is the source of the vast majority of the water found in the atmosphere, and also a substantial reservoir and source of heat. Yet most people don’t think of it having much impact on weather–perhaps weather is just the most obvious manifestation of the vast oceans–especially for those of us that live far inland.

Hi Willis,
if you did a careful analysis of my tables
-suggest you make hard copies –
you can make a no. of interesting observations
1) modern warming appears to be driven by an increase in maxima, not minima. It is the increase in maxima that happen during the day that drives up the average temp. and also that of the minima.
If it were minima (that happen during the night) pushing up the average temp.s we should agree that an increase in GHG’s was the cause of it. As it stands at the moment we have to conclude that the warming of our planet was largely natural.
2) Maxima increased both in the SH and the NH but if you look at average temps. (= Means) it appears that the global warming is not really global. It would seem that in the NH, which has most of the landmasses, some of the additional heat (most probably caused by more sunshine and/or less clouds) is being trapped.
3) The difference in the warming of the NH and the SH again proves that it is not the the increase in CO2 that is contributing to it. Namely the CO2 conc. is quickly everywhere the same on earth due to wind and diffusion. Therefore the warming should everywhere be the saem – if an increase in GHG’s were doing it.
4) The most likely cause that I find for some entrapment of heat in the NH is that it is due to additional vegetation.Namely if you look at my results of Tandil in Argentina, where there has been substantial de-forestation, you find it is actually cooling. In Norway and Scandanavia where there has been an increase in forests, there it is warming.
So, I think, yes, the increase in vegetation does trap some heat, leading to some increase in the average temperature.The question is how much? Why do they bring CO2 in the equation when clearly it has nothing to do with it, apart perhaps from working as an accelerator for growth. Could this warming not be easily determined in real big greenhouses?


It is not possible to generalize climate throughout the Miocene. Sequence stratigraphy has been used to develop a detailed sea level record, and it shows global swings as large as 250 meters. It is assumed the sea level changes are driven by changes in glacial mass. Clearly, the climate had strong drivers other than CO2, and global temperatures fluctuated through a broad range.