Have you ever thought about where fresh water comes from? How it gets here? Ok, yes... rainfall brings it. But do you know how and why rain falls across the breadth of the land? Or possibly- why it doesn't?
Atmospheric physicist Millán Millán of Spain (1941-2024) remembered how, when he was a boy in the 1940's, there were daily summer rainstorms in his homeland. In the 1970's, he was asked to determine why those daily storms had disappeared from the western Mediterranean region, leaving the land much drier.
He found that, along the coast, marshes had been eliminated, and land had been deforested, industrialized, developed, and paved. His research revealed that, prior to those land cover changes, evaporation from the marshes and transpiration from forests had added enough moisture to the sea breezes to cause condensation and daily summer rainfall.
But because of the change to the land cover, the land surface was now much warmer than it had been. And with the elimination of the marshes and forests, moisture was no longer being added to the incoming air, so its water vapor content was insufficient to
cause precipitation. The daily rains came no more. The land became drier and hotter.
 |
| A deforested, dry Mediterranean landscape |
In our 2024 film "The Return of Old Growth Forests", the Biotic Pump theory was presented by its co-author, atmospheric physicist Anastassia Makarieva, who described how large, contiguous, old natural forests bring fresh water inland from oceans during photosynthesis by transpiring water vapor into the air. That water vapor leads to precipitation, creating a feedback loop that keeps water vapor coming inland and the land hydrated; forests bring water to themselves, and us. That's part of the Earth's hydrological cycle. Furthermore, with contiguous forest cover, water is effectively "pumped" across continents. As a result, not only do we get a terrestrial fresh water supply, but our climate is regulated, stabilized, and moderated as well. But that biotic pump mechanism can be shut down by degraded, interrupted, or eliminated forests.
For decades now, we've been hearing considerable discussion of how greenhouse gases, particularly CO2, cause climate change. But what has been almost totally ignored is the effect that alteration of land cover has on our climate. It's not just about carbon, and never was.
Keeping the land hydrated is crucial to terrestrial life, but that lesson has been learned the hard way. Many cultures have destroyed the very thing that makes the land habitable... forests. Places such as Egypt, Africa, Australia, and others, have become deserts because their forests were cut to the point where the hydrological cycle was disrupted, the soil dried out and could not recover on its own (ie, it became a "landscape trap"). That destructive behavior is still happening today in places like Canada, America, Chile, and the Amazon, putting those places also on the trajectory to desertification.
And change to land cover, especially the cutting and removal of forests, is what Millán Millán referred to as "the second leg of climate change." The greenhouse gas effect is just one half of the climate change story; land cover change is the other half, and just as important.
This story is told in much more detail in our new film, "Old Growth Forests - Nature's Biotic Water Pump". Sadly, Millán Millán passed away in 2024, but we hear his words in the film, thanks to audio from an interview Alpha Lo of Climate Water Project (on Substack) did with him. Anastassia Makarieva has become world renowned for her continuing research on the critical role of forests; in this film, she adds more information about the biotic pump mechanism. And we thank her for the invaluable help and guidance she provided. She too has a Substack site.
You might also like to read the interesting story of Millán Millán; Rob Lewis relates it on his "The Climate According to Life" Substack site.
The film will be available on the New England Forests Youtube channel April 20, 2025, at 6pm EST.
