Are Trees Making Climate Change Worse?
A dark downside of dark trees
Forests are generally assumed to play a vital role in the fight against global warming. After all, they absorb carbon dioxide (a greenhouse gas) from the air and store carbon in their trees and soil.
But a new study suggests planting the wrong kinds of trees could be making global warming worse.
The study, published in the journal Science, claims forest management practices in Europe that have tilted the tree balance toward dark green conifers has done more to encourage global warming than to combat it.
Many European countries have planted dark-color conifers such as the Scots pine, beech tree and Norway spruce because these trees grow faster and are more “commercially valuable” than other trees, according to the study authors.
But there’s an apparent downside. The conifers’ dark needles absorb more solar radiation than lighter leaves. In other words, they retain heat. They also release less cooling water into the atmosphere through evaporation. This causes the temperature in the forests to rise, adding heat to our already-warm atmosphere, the authors contend.
"Due to the shift to conifer species, there was a warming over Europe of almost 0.12 degrees," Kim Naudts, PhD, lead author of the paper, told the BBC.
While broad-leafed trees, such as oak and birch, take longer to grow, they reflect more sunlight back into space, according to the study. Unfortunately, many of these lighter-colored trees are cut down for building materials and other uses.
According to the researchers, conifers have replaced almost 400,000 square miles of broad-leafed trees in Europe since roughly 1850.
While this study was restricted to Europe’s forests, the researchers note similar effects in other parts of the world that have forest planting programs, including the United States, were likely.
The idea that some trees may contribute to global warming is not new. One study published more than two decades ago showed expanding forests in cold, snowy areas could raise the temperature because snow reflects more light (and heat) back into the atmosphere than dark trees.
Meanwhile reforestation efforts continue. Delegates at the 2015 Paris climate talks urged world leaders to plant more trees as a way to slash the greenhouse gases responsible for climate change. The World Resources Institute seeks to line up $2 billion a year to restore 100 million hectares of Africa by 2030.
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