Global Forests: Nature’s Vast but Overlooked Cooling System

Written by Myles, PSI Researcher

A little known fact about trees is that 90 percent of the water they remove from the ground is released directly into the atmosphere as water vapour. Therefore the depletion of our forests impacts the hydrological cycle which, in turn, influences atmospheric temperature. forests and water vapor


What are researchers discovering?

   “Trees can reduce air temperature by blocking sunlight. Further cooling occurs when water evaporates from the leaf surface. The conversion of water to air vapor — a chemical process — removes heat energy from the air.

  • A tree can be a natural air conditioner. The evaporation from a single tree can produce the cooling effect of 10 room size air conditioners operating 20 hours a day. 

“New research concludes that evaporated water helps cool the earth as a whole, not just the local area of evaporation, demonstrating that evaporation of water from trees and lakes could have a cooling effect on the entire atmosphere.”


   Naturally keeping a forested area means more water vapour and more clouds can form and cool the region by reducing the incoming sunlight.

   Therefore if you reverse the process and remove the trees there is less water vapour, fewer clouds, more shortwave radiation from sunlight-warmed Earth.

   Add to this reduced water vapour causing reduced precipitation, rainfall is well known to cool the climate, and you have deforestation as a significant factor in global warming. Large scale deforestation has been reported to cause between 30 to 80 percent reduction in precipitation to the local area. The definition of a DROUGHT is   ”A prolonged period of abnormally low rainfall” so it is accurate to state that deforestation is a cause of drought. 

   “Deforestation results increase temperatures due to the reduction in the cooling effects of evapotranspiration caused by loss of vegetation (Snyder, 2010). This also contributes towards reduced cloud formation (Castillo & Gurney, 2012)”.

Intact tropical

      “Models by Snyder (2010) indicate that deforestation in all three major tropical forest centres would cause increased air temperatures within the forest regions of 2- 3°C. For example,

the Amazon region is predicted to warm by 1.88°C between September and November.”

  • NASA put it like this:                           

Climate Impacts: Rainfall and Temperature


Up to thirty percent of the rain that falls in tropical forests is water that the rainforest has recycled into the atmosphere. Water evaporates from the soil and vegetation, condenses into clouds, and falls again as rain in a perpetual self-watering cycle. In addition to maintaining tropical rainfall, the evaporation cools the Earth’s surface. In many computer models of future climate, replacing tropical forests with a landscape of pasture and crops creates a drier, hotter climate in the tropics.


THE IPCC overlook the cooling effect of forests completely and put it like this:

IPCC AR5 findings with respect to tropical deforestation and land use change:

Net carbon emissions from land-use change during the past decade (mainly from deforestation) are estimated at 3.3 billion tonnes of CO2e[1] annually – around 10% of all human emissions. Carbon emissions derived from land use change continue to be a major contributor to global warming only superseded by the burning of fossil fuels.

It goes on to say “Tropical forests are some of world’s richest and most valuable forms of natural capital and are being degraded on an unprecedented scale due to an increasing population and changing patterns of consumption. They pump water around the planet, remove CO2 from the atmosphere, support the wellbeing of hundreds of millions of people and underpin the economies of entire regions.”


   Here highlighted is a reference in their own report that the cooling system described is a type of “pump”. It is in fact known as the “BIOTIC PUMP” and disturbance of this pump has been shown to cause significant warming and climate change. The introduction to a paper detailing some of these changes states.

Abstract: Intense condensation associated with high evaporation from natural forest cover maintains regions of low atmospheric pressure on land. This causes moist air to flow from ocean to land, which compensates the river runoff. Deforestation induces large-scale desiccation by disrupting this flow. Here we overview this theory and quantify the horizontal pressure gradients that govern the continental moisture supply. High evaporation and large extent of natural forests guarantee both a stable and high throughput hydrological cycle. Forests protect a continent against devastating floods, droughts, hurricanes, and tornadoes. Sustaining natural forests is a sound strategy for water security and climate stabilisation.


   “Deforestation Statistics Worldwide

The statistics of deforestation reveal that seven countries of the world amount to around 60 percent of the total deforestation on the planet. These seven countries include Brazil in Latin America, Canada and the United States in North America, Indonesia and China in Asia, Russia in Europe and the Democratic Republic of Congo in Africa.

The data compiled by the World Resources Institute reveals that the planet has already lost 80 percent of its forest cover to deforestation…”           Source: World Preservation Foundation.

   This figure of 80 percent includes all time loss due to the growth of civilisation. The estimate is of 1.9 billion hectares lost since the industrial revolution.  For a contemporary statistic we can look at deforestation annually.

   Taking the top 10 countries with highest deforestation and adding the tropical deforestation zones together totals 6,118,607 hectares lost annually. The boreal deforestation zones make up 747,400 hectares of this.

It is argued that the boreal deforestation has a net cooling effect due to snow being able to settle where the tree once was and increase albedo. But also the removal of the trees reduces water vapour which reduces clouds and rainfall which causes warming. Plus there is a recorded decrease in CCN (Cloud condensation Nuclei) related to deforesting the Boreal regions. So un-decided.

 But if you subtract the boreal forest with its possible cooling from the tropical letting some cooling cancel out warming this results in a net warming from 5,371,207 hectares of deforestation per year that has been falsely attributed purely to CO2.


   This is an extra 5.37 million hectares annually which will then have reduced cooling from evaporation, reduced cloud cover and reduced precipitation with its related warming. 

   A variation of 4-5 percent of cloud cover worldwide results in a 1 C change in temperature so any variations must be taken into account.

    It appears the IPCC is overlooking a significant driver of global warming and falsely attributing warming in deforested zones just to the unproven CO2 theory. Disturbance of the “Biotic Pump” appears to be the major player in the deforestation, warming, climate change equation not CO2.

Read also: 

Forests as rainmakers: CIFOR scientist gains support for a controversial hypothesis

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Comments (1)

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    Charles Higley


    Good. Taking into account that the US has 50% more trees now that in 1950, we are in good shape for this effect. And, wight he S American rain forests growing back 50 times faster than they are being cut down, we are not in danger from warming there. It is the biofuels industry that is encouraging forest detraction to make room for stupid and expensive biofuels farming—here is a real problem.

    The increased allergies to gluten can be attributed to biofuels, not GMO grains. There are no GMO grains in the market as yet. But, as biofuels has driven up the price of corn because 40% of the US corn crop goes to ethanol production, many recipes in the food industry have switched from corn flour (no gluten) to wheat flower, inadvertently adding gluten to the product.

    We are not evolved for grain consumption. We are mainly carnivores and opportunistic fruit, vegetable, and tuber eaters. Grains were never a major component of the human diet until the invention of agriculture. It is not surprise that we have bad reactions to a food we are not evolved to ingest at this level.

    Similarly, the first studies of saturated fats and heart disease were done on rabbits. It is no surprise that the rabbits reacted terribly to their experimental diet. Rabbits are vegans and completely unable to deal with saturated fats at that level or cholesterol which is absolutely NOT part of their diet in the real world.

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