Planting forests in dry lands all over the world is unlikely to help in the fight against global warming and climate change, according to Israeli research that cast a question mark over massive tree planting projects being undertaken by countries such as China.
Trees absorb carbon dioxide when they photosynthesize to make food (sugars), and by removing the gas from the atmosphere, they contribute to atmospheric cooling. They also cool the climate by increasing evaporation (in much the same way as animals sweat to cool down) and contributing to cloud formation.
But they can also create heat because of a phenomenon called the albedo effect.
In cases of high albedo, light-colored surfaces, such as rocks and sand — as well as white clothing — bounce a big chunk of the sun’s rays back to the atmosphere. By contrast, dark surfaces, such as forests, absorb the sun’s rays and then radiate heat.
The albedo effect is one reason why the poles are heating up so quickly — high-albedo snow and ice are being replaced by low-albedo (dark-colored) water and exposed tundra.
While research has been carried out on the albedo effect of boreal forests (also known as taiga), whose birch, poplar and conifer trees wrap around the northern hemisphere south of the Arctic, the new research by the Weizmann Institute and the Technion — Israel Institute of Technology, published in the latest issue of Science, focuses on drylands, which cover 40 percent of the earth’s surface.