Water: The Untold Story. Evaporating Water Has the Power to Cool Its Surroundings. What is the Relevance to Global Warming?

When you step out of the bath or the shower or the pool, it feels cold. When you sweat, it cools you off. This is the power of evaporating water. And yet “scientists” refuse to talk about it. Why?

It is little known and rarely discussed that water has the power to cool our climate. Water should be at the center of our conversation about climate change, but sadly it is not.

We experience the cooling power of evaporating water whenever we step out of the shower or the bath or the swimming pool. We feel cold because evaporating water makes us feel cold. 

It takes energy—and a lot of it, about 550 kilocalories per liter—to turn water from liquid into vapor. Evaporating water literally takes heat from its surroundings. This happens because evaporating water takes “sensible” heat, heat we can feel, and turns it into “latent” or hidden heat. The heat stays hidden as long as the water remains water vapor. The heat turns back into sensible heat when the water condenses, i.e., turns back into liquid form. (This happens up there in the clouds. But that’s another conversation.)

When we get hot, due to exercise or hot weather, we sweat, or perspire. Our bodies know that we need to cool off so we perspire.  Perspiration cools us off because perspiration is mostly water, and the water evaporates.  

Just as humans PERspire, plants and trees TRANspire. They exude water out of their leaves. This is why a shade tree or a forest is cooler than its surroundings, not just because of the shade, but because of evaporating water.

Water possesses dramatic power to cool the planet. But this only happens when you have enough plants working together to transpire water. This works best when you have a mature forest. That’s why we should protect our forests whenever possible. 

(Parenthetically: It’s usually possible, in theory, to protect a forest. But it depends on who is making these decisions and for whom. The decision of whether to protect or cut down a forest is usually in the hands of a small group of people who have no demonstrated concern for people or the planet. A big part of the challenge is to wrest control of decision-making from this tiny group of self-appointed decision-makers.

At this juncture, some people become concerned about too much government meddling where private property is concerned. But most people understand that just because a bird flies across my property does not mean I have the right to shoot it. It’s the same with timber. Forests provide public benefits such as cooling and flood control. Therefore deforestation impacts the public and has public costs, i.e., flooding and the loss of a solar powered air conditioner. Therefore, removal of a forest is not strictly a private matter.)

Back to our regularly scheduled programming … ;-) 

Water—as it flows through ecosystems—has the power to solve global warming by leveraging the power of evaporative cooling. Arguably, water has the  power to cool our environment in a way that is quicker, cleaner, and safer than anything currently on the mainstream agenda, i.e., lowering carbon emissions.

When “they” tell you about the urgent need to lower our carbon emissions, what “they” almost never tell you is how long it will take, even in the best case scenario, to lower the carbon content of the atmosphere. 

They also never discuss alternative means of cooling the atmosphere.

Cooling the atmosphere by lowering carbon emissions is a project that will take decades if not centuries. So what do we do in the meantime? Can we not also talk about the tremendous cooling power of water? Can we not talk about how we might utilize (nature-based) water cycles to cool our temperatures, while also lowering our carbon emissions? We can do both at the same time, right?

But we never hear this conversation. It’s ALL CARBON ALL THE TIME, baby! First 1) we’re going to talk about carbon emissions. And then 2) we’re going to talk about carbon emissions. And then, when we’re done with that, 3) we’re going to talk about carbon emissions some more.

In this article, There aren’t enough trees in the world to offset society’s carbon emissions – and there never will be , the author speculates that there will never be enough trees or forests to draw down all the human-caused carbon emissions. Maybe she’s right, and maybe not. It depends on your assumptions. (How much carbon we emit depends on whether we ever wrest control of decision-making from that tiny group of self-appointed decision makers referenced above. The self-appointed decision-makers are the type who fly around in their private jets and then tell the rest of us how we need to lower our carbon footprint.)

But the author, Bonnie Waring of Imperial College London, correctly asserts that forests, quite apart from their value as storehouses for carbon, provide valuable services in terms of wildlife habitat, water filtration and flood control. 

So far, so good. She makes points that we need to hear more often: That a forest is more than merely a storehouse for carbon. But what she never, ever says is that forests cool our environment by nurturing our water cycles. By nurturing our water cycles, forests cool their environment. By causing water to evaporate, forests cool their environment. It’s deceptively simple, and rarely discussed. 

What services do forests provide in relation to the water cycle? 

Forests cool the air through evaporative cooling. Forests cause prodigious amounts of water to evaporate though their leaves. According the the US Forests Service, a full-sized tree can transpire and evaporate 11,000 gallons of water per year. How much per day? If we assume that most of this evaporation occurs during the growing season, and we assume that the growing season is 220 days, then we get 50 gallons per day as the daily amount of water that the tree evaporates. And that’s just one full-sized tree.

Each gallon of water represents a measurable amount of heat removed from the air. The evaporation of one liter of water, about ¼ of a gallon, represents over 500 kilocalories of heat removed from the air. There is SO much for scientists to talk about here, if they were so inclined. But sadly, they are not. Only a few scientists are talking about this.

In addition to evaporation, a forest nurtures other aspects of the water cycle.

A forest causes condensation to occur, because the leaves of the trees emit condensation nuclei, such as bacteria and certain organic compounds. As such, forests cause cloud formation, because clouds are collections of water droplets, i.e., condensed water. Clouds make rain, so yet again, forests play a key role in nurturing our water cycles. 

Forests facilitate precipitation because they create a cool moist environment into which rain can more easily fall, as opposed to a hot, dry environment, into which a raindrop is more likely to evaporate before it reaches the ground.

And since a forest is a storehouse for water—trees are about half water, by volume—the forest plays a valuable role in regulating temperatures because water regulates temperature. Water warms up more slowly than air, so a water-rich ecosystem like a forest is slower to warm up and therefore is less likely to reach peak temperatures. Similarly, the water-rich forest is slower to cool down, and therefore is less likely to reach the lowest temperatures when it’s cold outside.

The same can be said of other types of ecosystems, such as wetlands, grasslands and savannas. They hold water and therefore provide valuable services that are not available when you degrade the ecosystem. 

Therefore, to the extent we want to leverage the benefits of our water cycles, we will work to protect these ecosystems, and restore the ones that have been degraded. Since water flows through ecosystems, the way we can save the flow of water is to save the ecosystem.

On land, the most visible manifestation of most ecosystems is plants and trees, so we should seek to cover the landscape with plants and trees, and protect places that are already covered with plants and trees.

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