Last week, Nadine Unger, an assistant professor at Yale University, published an opinion piece in The New York Times stating that the way to save the planet was to not plant trees. This opinion was wrong at so many levels that it is hard to cover them all here. There are many reasons why we need to protect forests and to plant trees—protecting water supplies, reversing the loss of biodiversity, ensuring that we have pollinators for crops, and sequestering carbon to reduce human-induced climate change.
There are all sorts of good reasons to keep forests around; reducing climate change is just one of them
The article opens with a discussion of the international REDD+ (Reducing Emissions from Deforestation and forest Degradation) mechanism, which aims to reduce tropical deforestation and enhance carbon removals from the atmosphere by re-growing tropical forests. Unger says it won’t work, pointing to an old argument about the offsetting effects of carbon release and the increase of energy reflection when forests are removed—the so-called albedo effect. The argument recognized that forests are dark (look at an aerial photo or a Google Earth image) and absorb solar energy, while agricultural fields and pastures are lighter and reflect solar energy. It’s the reason why a black car sitting in the sun with the windows closed gets hotter than a white one. So: forests absorb energy and heat the lower atmosphere. A 2007 study led by G. Bala (and others) published in Proceedings of the National Academy of Sciences showed clearly that globally deforestation would lead to cooling. The albedo effect surpasses the carbon effect in the energy balance, and the Earth cools when forests are removed.
However, and this is an important “however” for this discussion, when the authors looked at how the carbon and albedo effects played out at different latitudes, they concluded that the albedo effect overwhelmed the carbon effect at high latitudes (northern temperate and boreal forests) and the carbon effect overwhelmed albedo at low latitudes (the tropics). Stopping tropical deforestation and increasing tree planting in REDD+ countries, where the albedo effect is smaller than the carbon effect, makes sense from an energy balance point of view. This is why the international effort focuses on stopping tropical deforestation and rehabilitating degraded tropical forests. There is no REDD+ mechanism proposed for northern countries.
BLACK CARBON, RED HERRINGS
Later in the article, Unger trots out Ronald Reagan’s absurd statements about trees polluting and the importance of volatile organic compounds (VOCs) in the formation of tropospheric ozone and methane. She notes that VOCs, natural components of the atmosphere, react with other anthropogenic pollutants (particularly nitrogen oxides) to form these greenhouse gases. One would think that if VOCs are natural components of the atmosphere, the blame lies more in the newly introduced pollutants.
Not according to Unger. Atmospheric chemistry is full of non-linear processes—scientists figured these things out decades ago. When nitrogen oxides (also natural constituents of the atmosphere) are present in low concentrations, the reactions with natural VOCs result in the destruction of ozone and methane, so naturally these VOCs help keep the atmosphere clean. However, when nitrogen oxides are present in high concentrations as a result of human-caused pollution, VOCs react with these pollutants to produce more ozone and methane. So the problem is not that forests pollute. The problem is the unintended compounding problems associated with human pollution. Indeed, research shows that rather than trying to control ozone pollution by reducing VOCs, it would be more cost-effective to reduce pollution from nitrogen oxides. Cutting down the trees is the wrong solution.
Unger also completely skips over the issue of black carbon. When forests are cut and burned to prepare the way for agriculture, the fires emit back carbon into the atmosphere. This black carbon absorbs heat, like the aforementioned black car. When the fires that burn are on peatlands, it creates enormous other problems, such as the haze events that plague Singapore and other Southeast Asian cities from time to time.
Finally, Unger goes off on a strange tangent about oxygen. No scientist has ever suggested that deforestation would be catastrophic or even a little problematic with respect to atmospheric oxygen. There is no issue here—it’s a red herring.
There are all sorts of good reasons to keep forests around; reducing climate change is just one of them. One must question the motives of a scientist who grandstands on the eve of an important international conference that will give specialized attention to forests to cast doubt on the discussions. One must also question the motivations of The New York Times for printing such a piece.
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