MADRID, 19 (EUROPA PRESS)
Planting more trees would cool the climate and prevent fires, especially if planted in the tropics, according to a new study from the University of California, Riverside.
Published in npj Climate and Atmospheric Science, the research concluded that tree planting generally has a net positive impact on the climate, as it helps remove carbon from the atmosphere that contributes to global warming. However, local non-carbon-related temperature effects varied significantly by region. At higher latitudes, trees could have a slight warming effect, while in the tropics, the opposite is true.
"Our study found greater cooling when planting trees in warm, humid regions, where trees grow year-round. Tropical trees not only absorb carbon dioxide from the air, but they also cool themselves by releasing water vapor," James Gomez, the study's first author and a UCR graduate student, said in a statement. "It's not that planting elsewhere doesn't help—in fact, it does—but the tropics offer the highest yields per tree."
These findings mirror the results of a previous UCR study showing that planting trees could cool the planet's surface even more than previously thought. While that study considered the chemical effects of trees' interaction with the atmosphere, this one focuses more on understanding the physical effects of tree planting.
These effects include evapotranspiration. Tree roots draw water from the soil, which then rises up the trunk to the leaves. When the pores of the leaves open so the tree can absorb carbon dioxide for photosynthesis, some of the water evaporates. This process cools the air at the ground's surface and also cools the tree.
HOW SWEATING COOLS THE BODY
"It's similar to how sweating cools the body," Gomez said. "In the tropics, trees always have water available, which increases transpiration."
Trees can also reduce the amount of sunlight reaching the planet's surface. By emitting water vapor, the air can become more humid. Higher humidity can mean more clouds, and water vapor itself can absorb some of the sun's rays. Both effects reduce the amount of sunlight reaching the ground, producing a cooling effect.
The physical effects of tree addition produce a weak global average cooling of 0.01 degrees Celsius, although this cooling becomes significant in the tropics at about 0.1 degrees, and some tropical regions such as central Africa experience cooling of up to half a degree Celsius.
Accounting for carbon sequestration from tree additions is expected to amplify these cooling effects by approximately 0.15 degrees globally. The researchers note that more precise estimates of carbon sequestration effects will be explored in a future study, where the physical and carbon cycle effects of establishing new forests will be interactively simulated.
"Although the non-CO2 effects are small, it's good news that they're not causing warming, as previous studies have indicated is likely," Gomez said.
For this study, the researchers also used a relatively realistic scenario: planting trees in places where they had been cut down, avoiding deforestation, and limiting new tree planting to places where they wouldn't displace people or take up too much agricultural land. Furthermore, the experiment used data from 12 climate models commonly used for international policy analysis, so the results would be more reliable than relying on a single model.
THEY RESIST FIRE BETTER IN THE TROPICS
The researchers also discovered that, in some cases, trees can have a fire-suppressing effect. "In tropical savannas and other places around the world, trees are much more fire-resistant than grasses," Gomez said.
However, the study found that in some areas of Canada and the northeastern United States, trees would likely cause more fires and reduce cooling by absorbing too much sunlight.
"This is not an invitation to get rid of the trees growing there! They offer multiple benefits for ecosystems and biodiversity, reducing CO2 and cooling the surrounding areas," Gomez said.
"What we need is an ideal area of trees in each region. Just the right amount to achieve the strongest and most positive climate effects."
