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Trees and Weather

For many, celebrating July 4th brings out patriotic sentiments, a sense of marvel at our country's founding, its multi-century endurance and appreciation for the clear articulation of rights made by our founders as to the underlying and undeniably humanist principals of our democracy.

Among those in the nuclear industry, we are also celebrating the successful achievements of several innovative nascent criticality events among other sector advancements, marking the impending arrival of a new generation of advanced reactor designs, which some have taken to calling the "Golden Era of Nuclear Power."

These technical achievements are truly inspiring but the moment is overlaid by record-breaking heat conditions, reminding us of the frightening reality that climate change is here. It is already dishing out scorching heat, strained energy systems, devasted agricultural and forest areas, declining wildlife, hotter and more acidic oceans, extreme weather events and increasingly taking lives and/or destroying livelihoods.

For those suffering from extreme heat this July 4th weekend, as millions in Europe and the eastern coast of the U.S. currently are, there is both good news and bad news. The good news is that if you can get somewhere where there is air conditioning, you won't die from the 100+ ∘ F heat. Probably you'll feel quite comfortable, so long as your power stays on and your air-conditioner continues to work—even though the energy powering your air-conditioner (with a few exceptions) is simultaneously making the planet hotter.

The bad news is that humans appreciate mechanical air-conditioners that cool a room or a building a lot more than they appreciate nature's most perfectly evolved biologic form of air conditioner: trees and forests. It turns out, if we want better protection from the extreme heat that our emissions are causing, we need to protect forests from senseless destruction. Their enormous and yet under-appreciated capabilities for regulating temperature, moisture, air pressure and wind have developed over millions of years and they use exactly the same physics to cool the earth as your A/C works, though on a vastly different scale and with other added benefits.

Tragically, we have continued to devalue the importance of trees and forests—even many environmentalists see them just as a form of carbon storage—and so we have been destroying them at record levels. This is extremely shortsighted but the result of the fact that so few actually understand how complex and critical the role forests play, especially in a climate stressed world. If forests had had a founder like Elon Musk to make the global pitch to investors on how incredible tree technology really is and demand trillions of dollars in valuation for their services keeping earth inhabitable, the story might be different.

We don't. For now, the closest we have is Dr. Anastassia Makarieva of the non-profit, the Biotic Pump Greening Group, which is making the scientific, academic and social media case to help people understand how and why forests are such an important part of ensuring the livability of our planet. Reading Dr. Makarieva's substack, Biotic Pump & Biotic Regulation, will blow your mind with the descriptions of the physics involved in the mechanisms by which forests control wind, make rain, and cool the earth. But, in honor of the July 4th holidays, I'll save you hours of reading by condensing some of Dr. Makarieva's key points and explain why you should think of forests as planet Earth's continent-scale air-conditioners and rain-makers. Once you understand that, it become easy to understand that the fewer we have left, the hotter and drier it will get.

Dr. Makarieva has made the case that forests act as earth's biotic pump (which she describes as working a lot like a steam engine), helping to bring in warm air containing moisture that was evaporated from over the seas and help to wring the moisture out by causing clouds to form and stimulating pressure changes to allow rain to fall down while ejecting the heat out into the upper atmosphere, where the pressure differential causes the winds that push cold air out over the ocean again, where it sinks, warms, loads up on water and repeats the cycle again. Her concept of this atmospheric pumping action explains the essential physics underlying the processes that are actively controlled by the forests through transpiration, evaporation, condensation and other mechanisms, which run on the same core physics and principles — leveraging the physics of phase changes of water — to operate a form of planetary air-conditioning — at a wildly enormous scale.

An air conditioner is a form of reverse heat pump: refrigerant evaporates inside the unit, absorbing heat from room air (that's the cooling), then a compressor forces it to condense outside, dumping that heat outdoors. As a side effect, room air passing over the cold evaporator coil drops below its dew point, so water vapor condenses out and drains away — the air comes out both cooler and drier, which is why AC feels so much more comfortable than the same temperature at high humidity: dry air lets your sweat evaporate and carry heat away from your skin.

A forest does something structurally similar but runs as an open, self-powered loop rather than a closed mechanical one. Transpiration is the evaporator side: trees pump enormous volumes of water from soil to leaf and release it as vapor, and that phase change for the water absorbs latent heat right at the leaf/canopy surface — which is the literal, physical reason it's cooler under a tree, which is an evaporative-cooling effect (such as what an old-fashioned swamp cooler uses). The condenser side happens later and higher up: as that warm moist air rises and cools, the vapor condenses into clouds and rain, releasing the latent heat at altitude, where it's far easier for the planet to radiate it away to space.

In contrast, something Dr. Makarieva describes as the "Super Greenhouse Effect," explains why heat trapped near a humid surface can stop escaping altogether, thus generating truly staggering heat that the body cannot reject through sweat, and thus can often be fatal, such as the prolonged heat waves we are seeing now. Which is one of the many not well valued services provided by forests, which do the hard work of getting heat rising up and out into the upper atmosphere via cloud condensation, which explains why some regions are better protected from long, lingering heat waves and heat-related deaths than others.

Here's the elegant and magical part: what if a hightech founder told you that their technology required zero electricity to work and just pure solar energy? Would that make you want to invest? What if you could buy an air-conditioner whose refrigerant could keep circulating without needing any power? In Makarieva's biotic pump, condensation itself does that job. When water vapor condenses aloft, it removes molecules from the gas phase back to liquid, which falls as rain and causes local air pressure to quickly drop (a change we've all felt but didn't understand). That pressure drop is what then sucks in more moist and dense air horizontally from the ocean, which we experience as wind coming in from the ocean. This is what keeps the whole cycle running and keeps carrying  moisture from the ocean inland. Forests don't need a compressor or electricity because the condensation event at large scale is the compressor — it's a self-sustaining engine powered by sunlight (as a source of heat), physics which makes warm air less dense, thus lighter, gravity (which makes cold dense air sink) and biology (in the form of healthy, natural and diverse forests, which have evolved a bag of tricks that we still barely understand but which can add extra transpiration moisture, spores or other particles into the air to juice the pressure and moisture content that ensures that rain happens overhead.

Forests don't just provide cool shade: they manage temperature like an airconditioner, but they also manage humidity and rain. An AC's whole comfort payoff comes from pulling heat out of a room, producing a little waste moisture in the process. A forest does the opposite at landscape scale: by keeping transpiration high, it keeps atmospheric moisture concentrated enough to fuel that condensation engine, which is precisely what lets it "trigger rain at the right time, in the right place, in the right quantity" (as Dr.  Makarieva puts it) rather than just letting incoming moist wind pass over dry land with nothing to condense it. An AC discards the moisture it removes as waste. A forest's whole function is to control the moisture that keeps it alive and well, while maintaining enough moisture in the air that condensation and pressure differentials can keep the pump running.

Solving climate change is not a simple process. To stop increasing the forced warming of the atmospher, we must urgently transition away from carbon-emitting energy sources (both fossil fuels and biofuels), which is why the world is now working towards tripling or quadrupling nuclear power. But, because we already have too many large molecules in the atmosphere, we should try to prevent atmospheric warming where possible, by increasing global albedo (expanding areas that reflect solar photons back into space rather than allowing them to be absorbed (such as white roofs, grass, trees, forests and snowcover).  Additionally, we must begin to remove the excess carbon and methane from the atmosphere and ocean, through direct air capture, carbon dioxide removal, and other methods that will lead to reduce GHGs that serve as atmospheric warming elements. That work must also be done by energy sources that don't emit carbon, which is another reason to support the expansion of nuclear power.

Which is why so many of us are celebrating the achievements of the last year in nuclear, which have brought the emerging generation of Gen IV nuclear designs to a new level of readiness. But between now and when we have seen substantial progress towards the above goals, we are in for increasing levels of heat and discomfort. We must work collaboratively to protect what's left of the earth's natural forests — now down to just about 8% of available land — and even begin to regenerate them as the planet's only source of live-saving natural air-conditioning. Without these forests, we'll experience the worst effects of the heating that our emissions have caused as if we were standing out in the field on a hot, sunny day without the protection of the shade of a tree.

By Valerie Gardner, Founder and Managing Partner of Nucleation Capital and life-long tree hugger.

References:

BBC, Tropical forests destroyed at fastest recorded rate last year, by Mark Poynting and Esme Stallard, May 20, 2025.

Columbia University, Climate Science, Awareness and Solutions, "Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?, published in Taylor & Francis, February 3, 2025 by James E. Hansen, Pushker Kharecha, Makiko Sato, George Tselioudis, Joseph Kelly, Susanne E. Bauer, Reto Ruedy, Eunbi Jeong, Qinjian Jin, Eric Rignot, Isabella Velicogna, Mark R. Schoeberl, Karina von Schuckmann, Joshua Amponsem, Junji Cao, Anton Keskinen, Jing Li, and Anni Pokela

Biotic Regulation and Biotic Pump Substack by Dr. Anatassia Makarieva, an atmospheric physicist, along with occasional guest authors.

Biotic Pump Greening Group, explaining the technological marvels that are trees and working to restore degraded forests to make sure that they and their functionality is repaired.

David Roberts' Volts Podcast: How to keep people cool without making the planet even hotter, June 24, 2026, with Ankit Kalanki, unpacking the the hidden world of AC refrigerants.