19 January

Want to cool your planet? Try water!


We must challenge the CO2-centric action model as the only way to reverse climate chaos.

Traditionally, the scientific community has focused on greenhouse gases, particularly carbon dioxide (CO2), as the primary drivers of climate change. However, this perspective overlooks the critical role of water in Earth's climate system. For billions of years, Earth has sustained liquid oceans and a stable climate, largely due to water's unique capacity to absorb and transfer heat back into space.

While the sun's intensity has increased over time by 30% the temperatures on Earth have been quite stable and in fact have gone down by about 7 degrees Celsius on average over the last 100 million years.

This was possible because of the fast colonization by vegetation of the land masses, that led to more evaporation and irrigation of the much drier land before. The increase of biomass on land was crucial and especially the development of the rainforests, the champions of cooling through water. The role of water in the growth of the biosphere is second to none. Water in its various forms – liquid water, ice, vapor, and atmospheric haze – accounts for most of the Earth's natural heat dynamics, far overshadowing the role of CO2 and other greenhouse gases. And life, the biosphere and especially the process of photosynthesis, drives the water cycles of the planet both on land and in the oceans.

The climate models have predominantly attributed global warming and climate change to rising levels of CO2. These models often use water vapor as a secondary factor, a feedback mechanism amplifying the warming effect of CO2. However, this oversimplification fails to recognize the independent and dominant role of water in climate regulation. The concentration of water in the atmosphere, magnitudes higher than CO2 levels, is influenced not just by temperature but by a balance of aerosols that play a key role in changing atmospheric water from a gas to its liquid state, forming clouds and rain. It is the biosphere that regulates this and with that the temperature of the Earth.

We can actually stop the planet from heating up by not solely concentrating in reducing CO2 emissions, but by focusing on a second clear and hugely effective path of action - improving the Earth's natural processes to manage heat dynamics and climate balance, which is the water cycle, driven by the clever workings of the biosphere.

We must quickly re-examine our understanding of Earth's climate system and develop the right strategies to cool the planet with these new insights. Yes, we must reduce greenhouse gas emissions as fast as possible, but the sole focus on CO2 will get a lot of us killed in the decades ahead, because it is not enough! Let’s also focus on water to cool the planet!

We can actually stop the planet from heating up by not solely concentrating in reducing CO2 emissions, but by focusing on a second clear and hugely effective path of action

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The Amazing Properties of Water

Water is a remarkable substance and it has played an essential role in making planet Earth habitable for life in many guises and forms. The temperatures at the Earth’s surface are just right for water to manifest its different phases from ice to liquid and vapor and back again. To understand how this helps the energy balance on the planet, we must dive a little bit into the technical aspects of water as it changes from ice to liquid to gas and back.

The energies involved in going from one state of H2O to another are considerable; a total of 80 calories per gram or 334 joules of energy are required to melt 1 gram of ice at 0°C, which results in the now liquid water having 334 joules per gram more energy than if it were ice at the same temperature. That latent heat is released when the liquid water subsequently freezes. With most materials, the crystalline, solid form is more dense than in the melted state, but water is the grand and amazing exception. Consequently, ice is less dense than liquid water, and it floats. If that were not the case, during cold spells and ice-ages, the ice would have sunk to the bottom of oceans and lakes, leaving just a small layer of melt on the surface. If ice were heavier than liquid water, life as we know it would never have been!

As we all know when heating water in a kettle, still more energy is required to convert one gram of liquid water to its vapor, the latent heat of vaporization of water being 540 calories per gram (2,260 joules per gram). Essentially, that considerable quantity of energy is what it takes to separate the molecules in one gram of water, by breaking the binding hydrogen bonds, so that each molecule can float free as a gas, with characteristics not far removed from what physicists term an ‘ideal’ gas.

Liquid water will increase—after evaporation and turning into water vapor—1,244 times in volume. This has considerable consequences for the atmosphere when the water vapor in humid air condenses to form clouds. The abrupt volume change leads momentarily to a partial vacuum, followed by an implosion of air surrounding the point of condensation, which fills the space vacated by water vapor that has transformed to liquid. If enough water vapor is involved and the rate of condensation is high, the result will be a wave of air which moves vertically up from the surface to where clouds are forming. Vacuums are spaces waiting to be filled, and the upward flow of air will suck in the replacement from a horizontal current of air flowing over the surface. The consequence of cloud-forming on a big enough scale will result in a complete circulation of air and that is exactly what happens over the tropical rainforests of the Amazon Basin and elsewhere.

The power of water vapor condensation

When water gets evapo-transpired through the leaves of a tree or a plant, liquid water is turned into vapor carrying a lot of latent heat up into the higher atmosphere, cooling the surface. Whirling up, because it is lighter than air and helped by the right type of aerosols, the vapor turns to liquid water again in quite a violent process at cloud level.

The Biotic Pump

Anastassia Makarieva and Victor Gorshkov of the Petersburg Nuclear Physics Institute, in 2007, elaborated the original theory for the functioning of a biotic pump which, according to them, would enable the watering of contiguous rainforest, even thousands of kilometers from the oceanic source of humidity, such as is the case in the Colombian Amazon, some 3,000 kilometers distant from the tropical Atlantic Ocean at the same equatorial latitude.

Since the initial paper on the theory, Peter Bunyard, together with Martin Hodnett and others, confirmed from a large series of physical experiments that water-vapor-condensation must lead to air flow and its circulation, showing that water-vapor-condensation leads to measurable airflow. The biotic pump is not a theory but a real phenomenon that plays a crucial role in the maintenance of the biosphere on land and the regulation of the temperatures on Earth.

A cool watery umbrella and the export of latent heat into space

But there are more ways in which water in its many forms regulates the temperature of the planet. The dense cumulus-nimbus clouds which form, mostly in the mid to late afternoon, over the tropical rainforest have a relatively high albedo and will reflect a considerable proportion of the incoming sunlight back out to Space.

At recondensation at cloud level not only do clouds form, but a second important phenomenon happens. The latent heat that has been transported up from the Earth’s surface gets released in the form of infrared radiation when the water molecules turn back to liquid. That radiation partly escapes immediately into outer space and partly heats up the tropopause of the atmosphere where the heat gets picked up by high altitude winds and slowly dissipates back into space.

Taken together all these cooling effects from the water cycles makes it possible to counter the global warming caused by ecosystem destruction and greenhouse gas emissions. More forest will lead to an increase in biomass and, therefore, to an uptake of carbon dioxide, but more importantly, it will lead to increased albedo, the stimulation of more biomass and the increased export of latent heat; first from the Earth’s surface and, at subsequent recondensation, this heat gets transported back into space. The forming of clouds over the tropical rainforest, plus the export of latent heat energy from evapotranspiration, could result in as much as 80 per cent of the total daily solar input to the Earth’s surface being returned to space!

The drying out of the Amazon Rainforest: an urgent call for change

The terrible droughts of 2005 and now again in 2023 over the Amazon Basin tell us that the deforestation and forest degradation that has been taking place over the past 70 years, is having dire consequences on the flow of humid air from the tropical Atlantic Ocean. The reduction in evapotranspiration in the Eastern part of the Basin will result in less cloud-forming which, in turn, will have two consequences, namely a significant reduction in the power of the biotic pump and, with the resulting reduction in rainfall, a drying out of the forest and a decline in evapotranspiration. Dieback of the forest and its decomposition turns the Amazon Basin into a source rather than sink for atmospheric carbon, adding to greenhouse gas warming. Worse still, with the failure of the biotic pump and the forest die-back, the cooling from the export of latent heat energy will be much reduced.

In effect, the forest-generated hydrological cycle, from evapotranspiration to cloud-forming, acts like a vast natural air-conditioning heat pump. The thousand-fold expansion of liquid water, as it evaporates at the leaf surface, followed by the equivalent reduction in volume as clouds are formed, enables the transport of considerable energy in the form of latent heat.

The unprecedented drought affecting the Amazon in 2023 is a worrying sign that the flow of humid air provided by the Trade Winds from the tropical Atlantic Ocean is no longer adequate to generate the atmospheric rivers of humidity which flow over the Basin to the Andes, from where they are then deflected southwards. The implication is that the deforestation which has occurred over the past few decades has taken its toll on the biotic pump, and has put the hydrological regime beyond a threshold from which it may not recover. The conclusion is that deforestation in the Amazon Basin must cease and every effort expended to bring about regeneration. And yet, the forest is razed and burnt, not just by Brazil, but by Bolivia, which appears intent on converting its Amazon rainforest into agriculture.

A careful calculation of all of the cooling effects of water in its interaction with forest in the tropics has brought us to the conclusion that if we are able, in a short period of time, to reforest an area of 250 million hectares of now barren, open land in the tropics, or convert those areas to agroforestry, the combined cooling impacts of the restored water cycle effects would be enough to stop the planet from heating up further, giving us time to decarbonize the global economy.


When we think of water, it is mostly about the water that surrounds us in its liquid form or as snow and ice, but only when we understand water in all its forms and how it is key to all aspects of the climate, do we start to understand what a powerful substance it is to keep the world cool, creating optimal circumstances for life on the continents to thrive. Especially in the tropical zone where most solar energy comes in, evolution has formed cooling organs of the planet in the form of tropical rainforests which in a continuous process of photosynthesis, evaporation, recondensation, cloud formation and precipitation also form wind that take water into the interiors of the continents and exports huge amounts of latent heat, first taken from the Earth’s surface back into space. Water, in its interaction with the biosphere and the atmosphere, is the true champion of the planet’s temperature regulation. As soon as we understand that, we can fight climate change much better than by solely focusing on the other greenhouse gases.

Water, in its interaction with the biosphere and the atmosphere, is the true champion of the planet’s temperature regulation.

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The significance of the means by which the planet cooled itself those millions of years ago should not escape us and, to combat global warming, we must urgently undertake the recovery of forests, at the very least, in those areas which have been deforested since the industrial revolution of 250 years ago. This will then restore the hydrology over those areas and help the planet to regain its capacity for homeostasis.

This article was co-authored by emeritus professor Dr. Peter Bunyard, who studied Natural Sciences at Cambridge and Harvard, and lectured at the university of Bogota on the climatic importance of the Amazon rainforest. 

He was a  founding editor of The Ecologist magazine, he is a Fellow of the Linnean Society. He is one of top global experts on the biotic pump and has co-authored more than 30 books. 

Now retired he is currently working on a book called Cooling Climate Chaos with Rob de Laet.

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