New research hailing out of Carnegie’s Global Ecology department has discovered that evaporated water from trees helps cool the Earth as a whole — not just a specific area.
Scientists have long researched and explored the ideas around the impact on global climate from 
the water that is evaporated from trees and other vegetation.
This new research reinforces these ideas. The researches have found that not only does the evaporated water help cool the local areas around the trees, but also given back to the Earth as a whole. Therefore, the evaporation of water from the trees, lakes, and vegetation may have a cooling effect on the entire atmosphere.
These discoveries have major implications for making decisions when it comes to land use. The trees go through a process called Evaporative Cooling. This is when a local area is cooled by the energy that is used in the evaporation process: an energy that generally would have heated the area’s surface.
Research has already shown that deforestation and creating more paves areas can contribute to global warming. This is because it decreases the local Evaporative Cooling. However, what researchers have not yet discovered is exactly whether this decrease in evaporation would also directly contribute to global warming.
Because of the emissions of carbon dioxide, the clearing of rainforests, the consumption of meat, the overuse of energy, and other factors, the Earth has been getting increasingly (and perhaps alarmingly) warmer over the past years. But these discoveries in water vapor were not well understood, especially in relation to the global climate effects they would have.
In addition, water vapor acts as a greenhouse gas in the atmosphere, so researchers believed it was possible that this evaporation could have the opposite affect on the global climate: a warming one. The energy that is taken up in evaporating water is released back into the environment when the water vapor condenses. This, then, returns to earth, mostly as rain. This cycle of evaporation and condensation moves energy around, but because it cannot create or destroy energy, evaporation cannot directly affect the global balance of energy on our planet.
The researchers were led by George Ban-Weiss, and included Long Cao, Julia Pongratz and Ken Caldeira, and Govindasamy Bala. Using a climate model, the team found that increased evaporation actually had an overall cooling effect on the global climate.
This type of increase in evaporation tends to cause clouds to form in a lower area of the atmosphere, which acts as a reflection to the sun’s warming rays back out into space. This has a cooling nature on the environment.
Their new study shows that the evaporation of water from trees and lakes in urban areas helps keep our cities, as well as our whole planet, cool. The research further shows that it is necessary for us to understand how daily activities can change the climate both locally and globally.
The study was published September 14th in the journal Environmental Research Letter.
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