In an oped in Saturday's New York Times (To Save the Planet, Don't Plant Trees), Nadine Unger argues that reducing deforestation and planting trees won't help fix climate change but will rather make it worse. One might ask how the 2,000-plus scientists and experts on Intergovernmental Panel on Climate Change (IPPC) got this one wrong – they found tropical deforestation a major source that must be reduced to control climate change – but in fact it's Unger who's way out on a limb here.
When trees grow, they absorb carbon dioxide (CO₂) from the atmosphere and store it as carbon in their trunks, branches, leaves and roots. When people cut the trees down and burn them to clear forest for cattle pasture or crops, as they have at a rate of 13 million hectares of forest per year in the tropics over the last decade, this releases CO₂ back into the atmosphere.
Unger argues that forests absorb more sunlight than crops or grassland, which reflect more sunlight back into space and cool the earth. But that's not true in the tropics. In tropical forests like the Amazon, where deforestation is happening and thus where the Climate Summit's attention is focused, trees take up water from rainfall and evaporate it through their leaves, and create cloud cover. These clouds reflect even more sunlight than grasslands or bare earth, thus cooling the earth more. This is why large-scale deforestation disrupts rainfall regimes – and why deforestation in the Amazon, if unchecked, may reduce rainfall in California.
Emissions from tropical deforestation are, from the perspective of the atmosphere, just the same as emissions from burning fossil fuels – carbon that was wood, coal, oil or gas is turned into CO₂ and released to the atmosphere. In a living forest, trees do die and, over time release CO₂ to the atmosphere. But then new trees grow, and absorb that CO₂ again – not the case when forests that have stored carbon for centuries are replaced by grass to feed cattle or oil palm plantations.
Contrary to Unger’s claims, the "high risk" is to ignore the 200 billion tons of at-risk carbon stocks in the world’s tropical forests. In fact, as the IPCC has concluded, stopping tropical deforestation is a critical priority for controlling climate change.