Necessary Forests: Forests as Biotic Wind Pumps

An intriguing theroy has been kicked around in the scientific world for more than a decade. It’s particularly timely right now as the world watches videos of Australia aflame.

Back in 2006 and 2007, two Russian scientists named Anastassia Makarieva and Victor Gorshkov proposed that forests have a central role in driving weather and climate for the entire planet. The theory, while controversial, explains phenomena that otherwise remain a mystery, such as how continental interiors like the Amazon and Congo can be as moist as coastal regions, and why Australia went from being a heavily forested continent to being heavily desert.

They theorize that vast forests generate winds that pump moisture across continents and around the globe. Here’s how: Gas occupies less space as it converts from a gas to a liquid. This is true when water vapor condenses to form droplets and clouds. Because the moisture takes up less space than the gas it formed from, local air pressure drops.

The next key is that evaporation is greater over forests than over oceans, so coastal forests have lower air pressure than the nearby sea. Thus they draw in moist air from the ocean, and the inrush of air generates winds that carry moisture toward the interior. As this process repeats itself in successive stages, moisture is cycled towards the continent's heart.

The total volume of water involved in this process would be almost unimaginable. The researchers suggest that, at least at the time they were writing, rainforests were sending more water into the atmosphere than evaporated from the surface of the world’s oceans. The Amazon rainforest, they said, was releasing 5.28 trillion gallons of moisture every day via evapotranspiration.

The implications of this theory are enormous. If it proves valid, it will transform our vision of forests and climate change, since even relatively minor deforestation could cause the heart of a continent to dry out.