It is not - as described in climatological models - the mass circulation of air which drives the hydrological cycle, but the hydrological cycle which drives the mass circulation of air.
Imagine being in one of the wettest rainforests in the world with three outstanding physicists concerned with the thorny question as to how is it conceivably possible for the rainfall to be as high, if not higher, thousands of kilometres inland than it is at the coast.
Indeed, Leticia, in the Colombian Amazon, on the border with Brazil and Peru, some 4 degrees south of the equator and 3,000 kilometres inland from the Brazilian equatorial coastline, gets more rain during the course of the year than the island of Fernando Noronha stuck out in the equatorial Atlantic Ocean and right in the path of the Intertropical Convergence Zone and the Atlantic Trade Winds.
How can that possibly be when the coast has been left far behind and rainfall, in the progression of the air mass from East to West, is constantly depleting the air of moisture, such that there should be an exponential decline of air moisture as one traverses inland? On that count, Leticia should be more a desert than a place of luxuriant biodiverse forest.
Well, I was lucky to have the answer straight from the very scientists who, as theoretical physicists, had conjured up an intuitively sound and logical explanation, however much it went against the grain of the thinking behind the generation of the best known climate models.
Finally - a theory that holds water
Indeed, I was with Victor Gorshkov and Anastassia Makarieva, both from the Institute of Nuclear Physics in St Petersburg, and with Germán Poveda of the Medellín campus of the National University of Colombia.
We were scrambling our way over the intertwining foot-holding roots of the Chocó rainforest, straddled along Colombia's Pacific coastline, in pursuit of those exquisitely-coloured poison arrow frogs which get their name from the blowpipe darts used by the Embera-Katío Indians of the region.
We weren't there to capture the frogs, just to see them in their glory, intense spots of colour against the drab brownish colouration of the humus bedded on the forest floor or perched conspicuously on the dark bark of a tree.
And, after some four hours of energetic clambering up and sliding down the slithery slopes on which the forest is rooted, we did indeed come across half a dozen or so of the tiny creatures. Seeing the frogs there in full display and with no attempt to hide made us realize that we were in a healthy rainforest.
The frogs get the precursors to their deadly heart-stopping poison from insects which themselves have fed on toxic leaves and, for the frogs to have their chemical protection from predators, the forest has to have its biodiversity intact.
No question, the Colombian Chocó with its plethora of species is one of the most terrestrial biodiverse regions in the world and how beautifully it is situated with the Pacific Ocean just a stone's throw away.
We were there, without electricity, without internet, without a host of tourists; we were in a sanctuary which gave us peaceful hours to reflect, to observe and to feel the omnipresence of the natural world.
Germán Poveda, a member of the IPCC and full professor in the Geosciences Faculty of the Universidad Nacional, had invited the two Russians to Medellín to give a three-day course on their biotic pump theory.
He also presented some of the latest evidence that the theory not only holds water but provides a better explanation than any other in accounting for climate processes involving convection by which air flows upwards, against gravity, and so sucks in air flowing over the surface to replace it (see Figure 1, above right).
It is hydrology that drives circulation!
In essence, Gorshkov and Makarieva claim both from their theory and from world-wide observations that the condensation of water vapour at cloud-forming altitudes brings about a sharp reduction in local atmospheric pressure such as to generate an implosion of sufficient strength as to suck up air from the surface.
That upwards-directed flow necessarily leads to air moving horizontally over the surface to fill the partial vacuum, and hence the idea that the trade winds, skimming over the surface of the Atlantic Ocean on their way from Africa to equatorial South America, are sucked in as a result of cloud formation over the Amazon's rainforests.
Above, where the clouds form, the easterly jet stream, associated with the Earth's spin Coriolis Force, adds its own suction to the process, such that the implosion of air as the water vapour condenses in cloud-forming can better suck upwards rather than downwards so generating the convection which we so readily see from satellite imagery.
That process, according to the biotic pump theory, explains large-scale convection. And even if heresy to say it, the theory dictates that it is not - as described in climatological models such as the GCMs, the General Circulation Models - the mass circulation of air which drives the hydrological cycle, but the hydrological cycle which drives the mass circulation of air.
If we accept the theory, the great tropical Hadley Cell Air Mass Circulation is therefore driven by the processes of convection which take place over the 6 million square kilometre Amazon Basin, the 'fuel' for that convection being contingent on the high rate of water vapour pumping from the closed-canopy vegetation.
Without the forest doing its work, we would have the Amazon Desert
And, were the forest to disappear, then according to the theory, moisture would no longer be sucked in and, given the natural fall-out rate of rainfall, some 600 kilometres from evaporation to precipitation, the land would dry out and in all likelihood turn to desert.
Were that the case it would be a disaster of momentous proportions, not just dwarfing the likely changes resulting from global warming but indeed compounding them.
As it happens, during the past 30 years of growing concern over the consequences of human-induced climate change, we have tended to ignore the hydrological role of rainforests and instead have focussed on the potential release of greenhouse gases, including carbon dioxide, nitrous oxide and methane into the lower atmosphere when a forest is razed and burnt.
Certainly, when deforestation was at its worst during the latter part of the 20th century as much as one quarter or more of the total of greenhouse gases released from all human activities, including the burning of fossil fuels, came from forest destruction across the tropical belt, from the Americas, across to Africa and on to South-East Asia.
We cannot deny that an increase in greenhouse gases must lead to more solar radiation in the form of heat being trapped at the Earth's surface where the density of gases is highest.
But while deforestation has always been of considerable concern, not least among biologists and ecologists, climatologists have been adamant that the surface winds will keep blowing with the same general patterns prior to any deforestation and that rain will still get deposited in the deep interior of continents such as South America or Africa, especially along the equatorial tropics.
Not quite 'business-as-usual', but the contention is that equatorial countries, such as Colombia, to the West of the Amazon Basin, will still get a substantial part of their rains derived from the tropical Atlantic Ocean, some 3,000 kilometres away, courtesy of the Trade Winds and the Walker Circulation which blows along the seasonally moving equator in what is known as the Intertropical Convergence Zone (ICTZ).
A reassuring prediction - no great change
That somewhat reassuring conclusion is predicted as a result of various theoretical studies, including those from the UK's prestigious Hadley Centre, which state that the consequences of widespread deforestation of the Amazon Basin, in all some six million square kilometres, combined with human-induced climate change, could cause a reduction in rainfall of around 12% to 15% in the Central and Western reaches of the Amazon.
No-one doubts that the recycling of precipitated water through vegetative evapo-transpiration will reduce significantly, by a half or more, when the forest has gone, yet, the general belief is that the surface prevailing winds, as exemplified by the Trade Winds and Walker Circulation, would continue to blow and carry the ocean-derived moisture with them.
Under such circumstances the rainforest would transform to savannah, much like that naturally found in Brazil's Mato Grosso, but not to the extent of becoming desert. For the great majority of climatologists, such an extreme consequence of deforestation is unthinkable, for the very fact that it does not fit their models.
But those models do not include the biotic pump theory of convection and therefore could possibly be dangerously deficient in their analytical predictions of the impacts both of global warming and in particular of deforestation.
Not that the accepted circulation models predict a benign consequence of Amazon deforestation: even a 15% reduction in rainfall constitutes a staggering amount, much more in fact, than would be needed to water the entire British Isles many times over.
But what if the hydrologists and climatologists are wrong?
What if the loss of rainforest were to have a devastating impact on the flow of surface winds such that they would no longer blow across the continental interior? What would happen to the rains then?
The biotic pump theory, based on standard physics, purports to show that surface winds are sucked in from regions where the condensation of atmospheric water vapour is relatively low to those regions where it is substantially higher.
The inference is that heavy cloud formation is more likely to occur over regions where water vapour generation is high, such as exemplified, par excellence, by the tropical rainforest which, through evapotranspiration from its leaves, pumps up more than double the quantity of water vapour per surface area when compared to the same latitude ocean.
On that basis, the high rate of condensation at cloud level, from some 2.5 kilometres altitude to 5 kilometres, brings about a sharp, well defined pressure change as the water vapour transforms into liquid water and ice.
The very notion that the surface convection of humid air is largely the result of the pressure change resulting from condensation is not one to be readily countenanced by hydrologists and consequently climatologists.
For them, it would mean they had left an important mechanism out of their models. Moreover they insist that, even though theoretically the pressure change is a reality, it would be substantially secondary in its effect on the lower atmosphere to the release of heat - latent heat - when water vapour changes from being a gas to become liquid or even solid.
Certainly the latent heat release, some 600 calories per gram of water vapour when it transforms to liquid and 80 calories more per gram when ice is formed, makes the air lighter and less dense where that transformation occurs.
That less dense, slightly warmer air will rise and thereby slow the temperature reduction caused by the chilling of air as it expands (the environmental lapse rate) and will push cloud formation and water vapour condensation higher.
Hydrologists and meteorologists also take it as read that, following any perturbance including condensation and latent heat release, the lower atmosphere will settle into a state of hydrostatic equilibrium.
In short, the vast majority of such scientists - I suspect many without properly studying the physics - repudiate what has become known as the 'biotic pump theory' and more or less assign it to the rubbish heap of conceptually flawed theories.
Without the Amazon forest, Leticia would be as dry as the Negev
However, Gorshkov and Makarieva have stuck to their guns, invoking fundamental physics as related to gases in the lower atmosphere and making reference to the differences between intra-continental rainfall when a river basin is well-forested compared to those with negligible forest cover.
Firstly they point out that the lower atmosphere cannot be in hydrostatic equilibrium when the surface atmosphere contains sufficient water vapour for condensation to occur, that being a destabilising process given the composition and pressure change as water vapour in its ascending reaches saturation at the dew point.
Secondly, they show that when forests are absent rainfall levels decline exponentially as one proceeds from the coast into the continental interior. That is in sharp contrast to intra-continental regions where forests cover the land, even as much as 3,000 kilometres from the ocean; there rainfall levels remain as high, if not higher than measured at the coast.
Leticia, in the Colombian Amazon is a case in point: it is some 2,500 kilometres from the coast and the prevailing winds and yet its annual rainfall is higher at 2,500 mm than that at Belem, near the Brazilian coast.
In taking that idea to its logical conclusion, Makarieva and Gorshkov refer to the dire consequences of widespread deforestation inland of the coast. If Colombia's neighbouring country, Brazil, were to deforest the swathe of native trees and vegetation all the way back to the Atlantic, Leticia would receive annually some 20 mm of rain, no more than can be expected in the Negev Desert in Israel (see Figure 2, above right).
That contention, disturbingly extreme, goes hard against the grain of climate model predictions. Not surprisingly, the rejection of the biotic pump theory has become a matter of creed, the claim being that it does not fit the facts and is based on a faulty interpretation of atmospheric dynamics.
The biotic pump is pulling the trade winds backwards over Colombia
So, what evidence do we have in the real world that the biotic pump theory is not just a misguided application of standard physics relating to gases, but better represents actual phenomena?
One telling example relates to the wettest equatorial rainforest in the world - the Chocó rainforest along Colombia's Pacific Coast. The puzzle is: how can the Chocó get as much as 12 metres of rain a year when the prevailing winds, therefore the Pacific Trade Winds, essentially move in the opposite direction, away from South America and towards Indonesia?
Our host and companion in our Chocó adventure, Germán Poveda, points to an extraordinary phenomenon: a portion of the Pacific Trade Winds, from both hemispheres, suddenly reverses direction and flows back over the Chocó to the Magdalena Valley in the central part of Colombia, where it clashes with the flow of air from the Amazon Basin that has passed over the Eastern Andes.
Colombia's rainfall patterns and turbulent weather in that region are determined by that encounter between the two streams of air.
Poveda, recognised internationally for his contribution to hydrology, has few doubts that the sudden, sharp reversal of the streams of air over the Pacific Ocean is primarily a consequence of the biotic pump in action with the rainforest pumping more water vapour into the surface atmosphere than anywhere else.
According to theory, that evapo-transpired water vapour provides the fuel for cloud formation and in consequence the sharp pressure change which follows the condensation of water vapour. It is that condensation which sucks back a portion of the westerly Trade Winds.
Nonetheless, the actual physical proof that condensation leads to surface airflow needs to be shown: that the physics underlying the biotic pump theory is not just correct, but that it is the force majeure driving atmospheric processes over contiguous rainforests, such as in the Chocó, the Congo, the Amazon Basin and seasonally, once temperatures rise and the sun shines, over the great boreal forests of Russia and the far North.
The solution: laboratory experiment
To seek answers and in the face of much scepticism, I therefore devised a way to experiment. The results show that the general physics used by Makarieva and Gorshkov to underpin the biotic pump theory is absolutely correct and that, in general terms, a corresponding surface airflow is induced when a sufficiently high rate of condensation is achieved.
The experimental set-up consists of two 5 metre high columns connected at the top and base such as to form a doughnut-like structure. The central 'hole' is used as a laboratory. The area throughout is 1 metre squared (see Figure 3, above right).
A double layer of copper condensing coils have been wound around the perimeter of the right hand column, just below the connection with the upper connecting 'tunnel'. The 'condensing coils' cover a surface area of some 1.6 square metres and are connected to an 'outside industrial refrigeration compressor with its own operating switch in the laboratory, some 4 metres away from the columns.
The airflow data is obtained using a 2-D ultrasonic Gill anemometer, placed in the top connecting tunnel where it meets the right column. The anemometer is 25 cm away from the top of the condensing coils.
In addition, three rotronics humidity sensors are deployed, one within 5 cm from the top condensing coil; one 1 metre from the base of the right hand column and the third, 1 metre from the base of the left hand column.
Two barometric sensors are used, one close to the top of the condensing coils and the other 1 metre from the base of the left-hand column. Thermocouples are deployed at various strategic points in both columns and the connecting tunnels. The sensors are either connected directed via USB ports (with serial / USB connector cables when necessary) and through using a Novus (Brazil) data logger.
The physics used to determine the results are standard. From the temperature (Kelvin), barometric pressure and relative humidity we can employ the Clausius-Clapeyron equation to determine the partial pressure of water vapour in the enclosed atmosphere at any moment during the experimental process.
Hence, knowing that water boils at 373 K when the atmospheric pressure is 1013.25 hPa (hectopascals and millibars) and, knowing the relative humidity and the temperature at any one moment from the logged sensor data, we can determine the partial pressure of water vapour (in hectopascals) as it changes at the point of condensation during the course of an experiment.
We can then relate our findings and compare them, at least in the form they take, with the measurements of airflow as determined by the anemometer.
It must be emphasised that the anemometer measurements, which include the directionality as well as velocity of airflow, are totally independent of the measurements of temperature, relative humidity and barometric pressure which together provide the necessary data to calculate the partial pressure of water vapour and the changes undergone.
The theoretical velocity of air at any one moment can be obtained from the partial pressure and air density changes, using Newton's kinetic energy equation.
Experimental results: the biotic pump is confirmed
The results are unequivocal: the calculations of partial pressure change and of airflow velocity match extraordinarily well the actual airflow as measured with the anemometer. Moreover, the directionality once condensation gets under way is always in a clockwise direction.
Critics of the conclusion that it is the rate of condensation of the water vapour which drives the airflow circulation during any one experiment follow the inherent belief that the airflow is actually driven by changes in air density.
Their reasoning goes that the cooling of the air when passing over the cooling coils makes the air more dense, which it undoubtedly does, and that the cool, denser air sinks and so forces the clockwise flow that we see measured by the anemometer.
Fortunately, straightforward basic physics enables the experimenter to calculate not just the partial pressure change at the point of cooling, but also the air density change at that point in comparison to the air density further down the column.
What we find is that the kinetic energy of the partial pressure change as water vapour condenses is at least 3,000 times greater for the same volume of air compared to the kinetic energy from the air become cooler and denser (see Figure 4, above right).
Without exception, all the experiments, with different initial temperatures and humidity, show that the airflow results practically 100% from the condensing of water vapour and minimally from the air density change.
Those results, currently from some hundred different experiments, indicate that the biotic pump theory has to be correct. Those concerned with scaling issues must realise that the macro physics involved in the experimental set-up is precisely the same as needs to be employed in the grander scale of the lower atmosphere.
Finally, at the end of each experiment we can gather the rain which falls from the condenser coils, as they warm, and compare the amount with that calculated theoretically from the total change in the partial pressure of water vapour.
The actual and theoretical coincide within a few grams: a nice proof that the physical theory behind the biotic pump theory accords well with reality (see Figure 5, above right).
In effect, a high rate of condensation of water vapour in the enclosed atmosphere of the experiment results in a process of convection which is surely comparable, although on a vastly different scale, to the mechanism which sucks in the surface air from over the ocean as a consequence of the high rate of evapotranspiration from the rainforest.
Coincidentally, the rate of condensation achieved in the experimental set up is of the same order of magnitude per unit area as that calculated to occur over the Amazon Basin - hence some 20 hectopascals drop in water vapour pressure.
I would suggest that scale is not an issue and what we obtain in the laboratory reflects reasonably well what we can expect in the lower atmosphere when there is a good covering of closed-canopy vegetation to pump up water vapour through its evapotranspiration.
Large scale deforestation is a global catastrophe in the making
The striking conclusion is that a simple experimental set-up has given us the proof that the general physics underlying the biotic pump theory of Anastassia Makarieva and Victor Gorshkov is essentially correct.
As such we can confirm that the consequences of wholescale deforestation, by whatever means, are likely to be far more severe in terms of intra-continental rain patterns than are currently predicted in climate models.
The hydrological consequences of deforestation are therefore far more important than greenhouse gas emissions resulting from the same deforestation.
Climate modellers, who, to date have studiously ignored the biotic pump theory when forming their complex circulation models, should indeed be worried that they have got the fundamentals wrong and that it is hydrology which drives the major air mass circulation rather than the other way round.
We destroy the world's rainforests at our peril for it is those very ecosystems which give us climate stability and enable our civilizations to flourish.
I have offered to host any physicist, including climatologists, who would like to use my experimental set-up to see for themselves the biotic pump principle in action.
As of now no-one has taken up my offer, not even from the nearby Met Office. I am waiting.
Also on The Ecologist:
- 'Brazil's ravaged forests are taking their revenge'
- 'Drought bites as the Amazon's 'flying rivers' fail'
- 'Drought hits São Paulo - what drought?'
- 'Five steps to save the Amazon'.
Peter Bunyard is a founding editor of The Ecologist and has since continued to write for it and more recently for Resurgence & Ecologist. He has written books on Nuclear Power and on Climate Change. One such book, 'Climate Chaos' was published in Spanish in Colombia in 2011. Recently, the University of Sergio Arboleda in Bogotá, Colombia, where he is currently carrying out research for the Institute of Environmental Studies and Services, has published in English his treatise on the Biotic Pump. He is giving a course this month at the University of the North in Baranquilla, Colombia on 'Climate Change and the Hydrological Cycle'. He is married and lives in Cornwall with his wife, Jimena, daughter and step-daughter.