More Trees, More Heat?

In the New York Times op-ed, “To Save the Planet, Don’t Plant Trees,” Nadine Unger challenges some of our conventional wisdom regarding climate change. We believe that by planting more trees, we’ll be able to slow or reverse global warming. But the science shows that it might have the opposite effect.

How warm the planet gets isn’t only dependent on the amount of greenhouse gases pumped into the atmosphere, but also on the color of the planet’s surface. That too, plays a role in how much of the Sun’s energy is absorbed by the Earth, compared to how much is reflected back to space.

The more the forest cover, the more dark green the Earth’s surface gets, the more it retains the heat, raising its surface temperature. By the same logic, a black shirt makes you feel hotter in July than a white shirt.

Sure, forests mop up about 25 percent of the world’s fossil fuel carbon emissions every year, by taking in carbon dioxide, and giving out oxygen.

[But] trees [also] emit reactive volatile gases that contribute to air pollution and are hazardous to human health. These emissions are crucial to trees—to protect themselves from environmental stresses like sweltering heat and bug infestations. In summer, the eastern United States is the world’s major hot spot for volatile organic compounds (V.O.C.s) from trees.

As these compounds mix with fossil fuel pollution from cars and industry, an even more harmful cocktail of airborne toxic chemicals is created.

Moreover, it is a myth that photosynthesis controls the amount of oxygen in the atmosphere. Even if all photosynthesis on the planet were shut down, the atmosphere’s oxygen content would change by less than one percent.

The Amazon rain forest is often perceived as the lungs of the planet. In fact, almost all the oxygen the Amazon produces during the day remains there, and is reabsorbed by the forest at night. In other words, it’s a closed system that [cycles] all its own oxygen and  carbon dioxide.

h/t: NYT

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