Planting forests in Africa and Australia may cool the planet

Planting forests can indeed moderate the rate of increase of carbon dioxide in the atmosphere, but not all forests are created equal. A new study by Weizmann Institute scientists, SRecently published in the scientific journal Scientific Reports, reveals that planting forests in semi-arid areas in Africa and Australia may rapidly and effectively affect the climate, thus offsetting a significant portion of man-made global warming.

For the purpose of the research, the research group of Prof. Dear Dan, from the Department of Earth and Planetary Sciences, a unique treasure trove of knowledge: data collected over 16 years at the Bitir research station - a planted forest at the edge of the Negev. The station, which is managed by staff scientist Dr. Eil Rotenberg with the support of KKL-Junk, measures the changes in the levels of carbon, water, heat, and other factors in the ecosystem of a forest growing in this area, which is semi-arid. Over the years, scientists discovered how these forests maintain an "energy balance" that includes heating and cooling mechanisms. For example, the forests can cool the ground beneath them, but the dark colored leaves trap the sun's radiation and release it as heat. Also, the forests consume water, but water also evaporates from them - and cools the air. The studies conducted by the group showed that a forest in a semi-arid region absorbs larger amounts of carbon than previously thought, but until the cooling effect of carbon fixation is felt, a long time may pass, due, among other things, to the fact thatThe dark leaves produce more heat than the light sandy soil.

Dr. Gil Yosef, at the time a research student in Prof. Yakir's group, decided to test whether the various factors operating in the model of Yatir Forest would also operate in a similar manner on a larger scale. For the purpose of the test, he chose two areas Arid to a similar degree - the Sahel region, bordering the Sahara, and a semi-arid region in northern Australia, and asked to see if extensive planting of "Yatir-like" forests would affect the climate in these areas Dr. Yosef and Prof. Yakir approached a group working at the University of Miami, Florida, led by Prof. Roni Avisher and Dr. Robert Volko. For the purpose of the study, the researchers used a sophisticated climate model, which allowed the group to perform simulations, and compare them to real data over 15 years. As part of the simulations, the group members added "trees" to the model that are similar to those that grow in the Yatir forest and are suitable for the local climate. The "trees" in the model had the correct leaves, root systems, height and density, and were "planted" in the simulation over large areas.

Prof. Avisher and Dr. Volko's model was a kind of telescope for studying changes in geographical areas that are only a few kilometers in area, with the possibility of broadening the view and examining patterns on the scale of continents. The model simulations - 15 years, based on real weather data - added and refined the The simulations, for example regarding variable amounts of precipitation.

"Large-scale afforestation in semi-arid areas may yield a greater profit than planting trees in areas found in high latitudes, for example in Scandinavia, and can be implemented in a relatively short time"

Dr. Yosef's simulations showed that the "planted" forests cool their environment at a level that exceeds the local level, and it is possible that they will even affect the regional atmospheric circulation so that the amount of rain that will fall over them will be significantly greater. Based on the model, Dr. Yosef estimates, that extensive afforestation in these areas, by itself, can lead to carbon absorption at a rate of about 10% of the total global biospheric carbon fixation, And thus help to cool our warming planet in about six years.

The main reason for this phenomenon, says Prof. Yakir, is that trees are excellent "water collectors": trees that thrive in semi-arid areas tend to develop deep roots. Therefore, when this happens in large areas, where millions of trees will grow, the trees will draw more water from the earth's soil, evaporate it through them, and thus cool the surface. Lowering the surface temperature creates a "domino effect" - in the end, both the decreasing amount of precipitation and carbon absorption improve; These two together significantly outweigh any negative, warming effect, resulting from the dark color of the leaves. In addition to contributing to the climate, the researchers point out, the forests can contribute to the people living in these areas in other ways as well - they can serve as a source of wood, add to their food sources, and provide them with employment and livelihood opportunities.

"Six years is the blink of an eye," says Prof. Yakir. "The result is indeed very surprising, but the model is quite stable. Large-scale afforestation in semi-arid areas may yield a greater profit than planting trees in areas located at high latitudes, for example in Scandinavia, and can be implemented in a relatively short time."

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The researchers estimate that extensive afforestation in semi-arid areas can lead to carbon absorption at a rate of about 10% of the total global biospheric carbon fixation, thus helping to cool our warming planet in about six years.

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