Rob de Laet
10 min readJul 15, 2022

(Or how we can cool the planet with forests.)

D. Ellison et al. / Global Environmental Change 43 (2017) 51–61 Fig. 1. Effects of forests on water and climate at local, regional and continental scales through change in water and energy cycles. (1) Precipitation is recycled by forests and other forms of vegetation and transported across terrestrial surfaces to the other end of continents. (2) Upward fluxes of moisture, volatile organic compounds and microbes from plant surfaces (yellow dots) create precipitation triggers. (3) Forest-driven air pressure patterns may transport atmospheric moisture toward continental interiors. (4) Water fluxes cool temperatures and produce clouds that deflect additional radiation from terrestrial surfaces. (5) Fog and cloud interception by trees draws additional moisture out of the atmosphere. (6) Infiltration and groundwater recharge can be facilitated by trees. (7) All of the above processes naturally disperse water, thereby moderating floods. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article: Trees_forests_and_water_Cool_insights_for_a_hot_world

All life on our planet depends on water, from tiny bacteria and sea urchins to huge elephants, whales and giant sequoias. Where you find water, you find life, even in extreme places like in boiling hot springs, in lakes below the Antarctic ice sheets or in deep dark caves or oceans where no light ever enters. Where you find life, there is water. Even a camel dies after a few weeks without the magic liquid. While water accounts for only 0.02% of our planet’s total mass, it has created a myriad of life forms over the last 3,8 billion years, including humans, a recent species that is currently devouring the planet’s biomass and other resources like a locust plague. But maybe more importantly and indeed largely overlooked, we have been very busy disrupting the water cycle everywhere, blissfully unaware of the effects it would have on life on our planet, including our own.

We all know that water cools, cleanses, sustains our bodies, refreshes our minds. It creates rivers and lakes and it rains on forests and meadows, forming gentle fogs to moisturize. It never likes to stay long in one place, likes to be on the move. It evaporates into the sky and rests as snow on the top of mountains and as ice packs. Without it we would die, but if this dance with life, called the water cycle, is out of sync, it throws the weather out of balance. Water is a bit like health, you don’t pay a lot of attention to it as long as you have it, but once it goes you are in big, big trouble.


So why am I telling you all of this? A fact almost always overlooked is that water vapor contributes around two thirds of the heat balance of the planet, while the total effect of water in all its forms is even larger, leaving the remaining contribution to the other greenhouse gasses, mainly CO2. So, the water cycle is by far the greatest factor in control of the Earth’s temperature. But the heat imbalance of the planet, currently calculated by NASA as 1,64 watt per square meter, is entirely attributed to CO2 and the other smaller greenhouse gasses. Isn’t that odd? Why is nobody questioning this? One of the big problems with water is that it is too capricious to model. It comes as ice, liquid water and vapor. It comes as low clouds, high clouds and fogs. It is everywhere in aquifers, rivers, lakes, vegetation, soils and so on. And it all the time dances around, it does not like to stay in one place for a very long time and depending on the place and phase it is in it has a different cooling or warming effect, whereas measuring CO2 is easy, it is almost evenly distributed over the whole atmosphere and its warming is a simple straight line on a diagram.


Forests have a very complex energetic interplay with sunlight, water and carbon dioxide. First of all, the process of photosynthesis cools the tropical rainforests by storing energy in biomass. Photosynthesis is an endothermic chemical process that absorbs energy from sunlight to turn carbon dioxide and water into oxygen and sugars. The solar energy is stored in the glucose molecules, ready to be used when needed for instance as food for animals, as detritus used by fungi and other soil creatures, or is released as latent heat in evaporation or sensible heat in a forest fire, for instance. In tropical rainforests probably between one and two percent of incoming solar energy is turned into biomass, while converting carbon dioxide and water into sugars and oxygen, lowering the amount of carbon based greenhouse gas in the atmosphere. That does not sound like a lot, but the current heat imbalance of the planet is less than one percent of incoming solar energy, so these amounts are of similar magnitudes.

We know water cools through evaporation. It cools our bodies on a hot day through transpiration. Could it be that it cools the planet too through transpiration? The simple answer is: yes, it does. And it does so additionally through evapotranspiration and a mechanism called the biotic pump, which was first described by Russian professors Victor Gorshkov who died in 2019 and Anastassia Makarieva.

The biotic pump is an interaction between forests, water and the atmosphere that makes trees pump up water to their leaves where they evapotranspire the water, while the trees simultaneously give off biogenic volatile organic compounds (BVOCs) that form the condensation nuclei for raindrops. Water vapor gets into an updraft from the trees higher up into the atmosphere where the water condensates around the BVOCs into tiny liquid rain droplets that form cumulus clouds. So the biotic pump cools locally.

The heat from recondensation of the water vapor into droplets is released higher up into the atmosphere in the form of photons that disperse into all directions with a wave-length that is not reabsorbed by greenhouse gasses, so a large part dissipates into space and this cooling decreases the planetary heat imbalance. At the same time, the recondensation lowers the air pressure, sucking in air from its surroundings, creating wind. So the evapotranspiration first cools the ground level of a forest by transforming incoming solar radiation into water vapor and creates wind. This vapor rises up into the sky, recondensates whereby a part of the heat escapes into space.

When the raindrops get large enough, they fall down as rain in a downdraft that also creates wind. So the biotic pump is a combination of the vertical up- and down drafts of water triggering horizontal flows of wind.

“Forests are complex self-sustaining rainmaking systems, and the major driver of atmospheric circulation on Earth,” Makarieva says. But the biotic pump is not only irrigating the land masses through rain making and wind creation. The forest leaves use energy to vaporize liquid water and actively transport that heat in the form of vapor up into the higher atmosphere and release that heat when it condenses back into liquid. Of the photons that escape in this process, a substantial part dissipates into space. On top of that it creates clouds during the day reflecting a part of the incoming solar radiation back into space and in the tropics often rains back in the afternoon and evening, again cooling down the surface, while clearing the sky for extra night time heat radiation back into space. In other words, forests function — through the biotic pump — as an air conditioner. Last but not least, the biotic pump makes sure that forests stay wet and that their soils stay wet and form sponges full of life that store a lot of carbon and water. As long as the soil has moisture, it allows photosynthesis to go on, while the ongoing evaporation keeps the forest floor cool. So forests cool both locally and the planet as a whole in several ways and these mechanisms are especially powerful in tropical rainforests.


So, if forests cool, then the question is, by how much? Antonio Nobre and Peter Bunyard are two scientists who quantified the total amount of water that is evapotranspired by the Amazon Rainforest and made the calculation of how much energy is involved in evaporating that much water.

See: How the biotic pump links the hydrological cycle and the rainforest to climate page 25

From there it is just a few steps more to compare the amount of energy involved to the total current heat imbalance of our planet. Here is the link to my calculation of energy transport Amazon and latent heat export into space.

The outcome is as simple as it is stunning: within the limits of uncertainty it shows that the total amount of energy the Amazon Rainforest transports from ground level to the higher atmosphere is of the same magnitude as the total heat imbalance of the planet. And from this amount of heat, almost half escapes into space. This is not in the IPCC climate models, because of wrong assumptions about the low albedo effect of dark forests, but they create clouds that increases the albedo over the area! This is a wrong trade off and a huge omission that completely changes the way we need to fight global warming.

See also Climate and Earth’s Energy Budget and Regenerate Earth — Walter Jehne

If we then add the fact that the cloud forming caused by the biotic pump actually increases the albedo of the rainforest area and cumulus clouds roughly have an albedo of 0,5 (they reflect half of incoming solar radiation), can we then assume that the Amazon Rainforest actually exports more than half of the total incoming solar radiation it receives back into space through reflection and the escape of photons into space?

If this is true, we can cool the planet fast and safely with forests and especially tropical rainforests!

Assuming the rough calculation is true, it means we can cool the planet fast and safely through a huge global program of tropical forest protection, reforestation and the transition to agroforestry with large shade trees. It means that if we are able to add an area the size of the Amazon Rainforest of tropical rainforests and agroforestry areas around the world (7 million km2), we will stop the heating up of the planet, apart from the carbon sequestration effect because regenerating forests and young agroforestry systems (3–20 years old) sequester between 10 and 20 tons of CO2 per hectare per year. Average this at 15 tons, the carbon cooling effect of an extra is ballpark 0,01°C per year or over 20 years, 0,2°C. (see tab carbon of the earlier calculation spreadsheet)

So together with the other measures that are slowly leaving the station: decarbonization of the economy, the energy transition, going circular, localization of economies and especially food and energy production and hopefully substantially lowering our animal protein intake, plus some natural based solutions we can apply to the oceans and programs like rock weathering, we can cool the planet by up to 1°C. If we start now, we should see the first year of cooling by 2040.

Let me also state something, that many will feel is very controversial: we need to get rid of fossil fuels as soon as possible, but if we do it too fast, the global economy will collapse with a holocaust almost as large as the ecological collapse of our planet. We will need to reform and localize our food production, at least halve our animal protein intake and shrink our transportation needs at the same pace as decarbonizing our economies if we want to avoid economic collapse. With the frontloading of the regeneration of nature in the tropics and the large-scale transition to agroforestry this exit from fossil fuels can be done in a manageable transition, which also gives politicians a feasible path to explain to the people.

Frontloading forest protection, reforestation and the transition to agroforestry and with that protecting and restoring biodiversity, is the fastest and most cost-effective tool, which, in combination with the other pathways, will bring better results than the Paris goals. Because let’s face it: at 1,1–1,2°C we are already in dire straits. At 1,5 °C the effects will not be manageable and while it is survivable for humans, it is not survivable for complex global societies with 8 or 9 billion people.


Well, the forests were hiding behind CO2 in a way. The 2013 Intergovernmental Panel on Climate Change (IPCC) fifth assessment report estimated the climate sensitivity of CO2 as between 1,5–4,5°C. Climate sensitivity is the amount of global warming we get if we double the amount of CO2 in the atmosphere. That is a huge bandwidth. Why is it so wide? According to researchers at Green Water Cools, who have systematically researched this climate elephant in the room, it may have been because the amount of global deforestation has roughly kept pace with the increase in CO2 in the atmosphere. So while we were destroying forests and with that the cooling capacity of the Earth, we attributed the heating to a higher climate sensitivity of CO2. It is very likely , but this needs more research that the huge bandwidth actually indicates that CO2 is only one third responsible for global warming and the destruction of the cooling capacity is causing possibly as much as the other two-thirds!

Indications that were already given in some research, like this one which describes the native American holocaust at the time of colonization and this article that very prudently calculates the cooling capacity of forests.


We are living in a time where the doom of extinction casts a shadow over our days. But this is not necessary. Not only does this research show that we can cool the planet. It has a lot more positive effects: if we implement a plan that is large and fast enough, we can stop the destruction of biodiversity on land, restore food- and water security to billions of people and pay rural people in the Global South for cooling the planet through climate finance, including carbon credits by creating climate-smart landscapes that protect nature and makes their food production resilient. In combination with measures to clean up and protect the oceans, we may still be able to turn things around and avoid wholesale collapse.

The investment in the protection and reforestation of tropical rainforests and the transition to agroforestry, will have a much larger cooling effect than the world realizes. It will also mitigate the effects of climate change in the Global South fast, slowing the increasing flow of refugees as economic conditions improve fast. And it gets even better than that. Everyone knows that large forests actually temper weather extremes. Large, healthy forests do not allow droughts, heatwaves or extreme flash floods to occur. They protect food production and slow down storms. So forests also calm extreme weather! If the world pays the tropical areas to regenerate their landscapes we can accelerate the fight against climate change and biodiversity destruction, while fighting global inequity. What’s not to like?

Rob de Laet, 7 July 2022

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With thanks to Pieter Paul de Kluiver from

Additional reading: Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes by Stefan Schwarzer

With regards to the phasing out of fossil fuels, this article is interesting to read:

With regards to the energy intensity of our current food production system:

A great lecture is this from Walter Jehne:



Rob de Laet

Will we make the transition towards a sustainable human culture and society or will we choose chaos? It is up to us to make the Great Turning. Let’s Go!