Forests sometimes cause warming

Forests in the tropics have a cooling effect on the climate four times greater than that of forests in temperate or subarctic regions. In winter, some forests in the northern regions have a net warming effect on the local climate. This is the conclusion of scientists from ETH Zurich. They included the previously ignored climatic effects of forests in their calculations of the climate benefits of trees. Their results appeared Monday in The nature of climate change.

Forests affect climate in two ways. First, because trees produce greenhouse gases that increase the temperature.₂ Pick up its wood, leaves and roots. This is the effect of the chemical climate of the forests. In the tropics, where the weather is warmer, trees grow faster and therefore release carbon dioxide faster₂ fixed this way.

less light

In addition, afforestation affects the climate through physical processes. For example, by changing the albedo, which is a measure of how much sunlight reflects off the Earth’s surface. Photovoltaic surfaces reflect a lot of sunlight, resulting in relatively less heating and therefore a cooling effect. Dark surfaces reflect less light (absorb more energy) and thus cause relative heating.

A forest covered with snow has less albedo than a plain covered with snow because the trees are darker than snow. Forests in snow reflect less sunlight, reducing CO2 cooling₂– Opposed to picking trees.

The leaching and evaporation of water by trees is another physical phenomenon that can lower the local temperature. This process consumes energy from the sun, which can no longer be used to heat the environment, and therefore has an additional cooling effect.

Sweating and whiteness

The relative contribution of transpiration and albedo varies by region and season. Sometimes they provide additional cooling on top of cooling by carbon dioxide₂Picking up, sometimes for even more warming. For example, the effect of albedo is greatest in temperate and subarctic climates, where there is abundant snow in winter. The effect of transpiration and evaporation is greater in the tropics, because temperatures are higher there.

These local differences have been known for some time, but researchers in Zurich have quantified them. As a result, policy makers can better include the effects of planting forests in their plans. Researchers convert observed temperature changes due to physical processes into carbon dioxide₂Emissions that would cause the same change in temperature (CO .).₂synonym). This allowed them to add these effects to the tree’s chemical carbon uptake. It turns out that forests in the tropics have, on average, almost four times greater positive climate impact than forests in the north.

Read also: This article discusses the role of trees as a means of addressing climate change

The study’s lead author, Michael Windisch, was so amazed at the difference between the different seasons, he wrote in an email: “In summer, all trees, even at high latitudes, cool their surroundings. Then the physical effects enhance chemical cooling by carbon dioxide.₂absorption, but in winter for forests in central Europe and even in parts of southern Europe the effect of local warming.” Then the cooling is carried out by CO₂The absorption is thus canceled due to diminished albedo.

herbs

Wouter Peters, professor of the carbon cycle at Wageningen University, who was not involved in the research, answers: “I think it’s a new and stimulating study. The approach in which researchers convert the effect of deforestation or reforestation on temperature to carbon dioxide.₂The equations are new and valuable.” However, he noted, researchers view the forest as a “very simple and isolated system.” This is a starting point, but researchers need to refine the approach in the future.

Nevertheless, the conclusions are valuable, according to Peters: “I have drawn from this study that at present only tropical forests are certain that their preservation and expansion have a positive effect on the climate. In more northern regions this is still the question. Therefore, it will be It makes sense to prioritize the protection of tropical forests in policy.”