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Forests, we know, absorb CO2 which helps curb global warming. These natural carbon sinks are the basis of offset programs, climate models, and most future-looking policy. Forests also absorb and retain heat, however, and new research is suggesting that, in at least one type of terrain, this heating effect outweighs the benefit of the tree's carbon capture.For 10 years, Professor Dan Yakir has been leading a Weizmann Institute research team looking at data from a FluxNet station in the Yatir Forest, at the edge of the Negev Desert. His research has showed that the semi-arid pine forest is a remarkably effective carbon sink, outpacing European pine forests and matching the global average.
When they looked at the total energy budget of the forests, however, they uncovered some unsettling results. They found that the dark-green trees absorbed a large amount of solar radiation, especially when compared to the nearby shrubs and desert. Furthermore, the cooling mechanism of the pine trees—in which leaves transfer heat to passing air currents—leads to a large amount of the absorbed heat being retained in the forest.
Together, these factors create a heating affect that, at least in the short term, surpasses the benefits of the forests' carbon absorption. Yakir explained:
Although the numbers vary with location and conditions...we now know it will take decades of forest growth before the 'cooling' CO2 sequestration can overtake these opposing 'warming' processes.
Semi-arid forests, like the one studied, cover an estimated 17 percent of the earth's land surface.
Desertification Could Cause Cooling
Yakir's team also looked at the impact expanding deserts had on heating and cooling. By applying their data to existing models they found that desertification, at least in the short term, actually creates a cooling effect by reflecting large amounts of solar radiation back into space. The result contradicts the common belief that desertification contributes to global warming.
The team estimates that, over the last 35 years, desertification of semi-arid land may have reduced warming by as much as 20 percent when compared to the rise expected based on CO2 increases.
Forests are Still Critical
It is important to note that this new data should not be interpreted as a rebuttal of the importance of forests. Indeed, the findings only comment on the short term impact of desertification and the heat retention of some forests.
In discussing his conclusions, Yakir was quick to comment that:
Overall, forests remain hugely important climate stabilizers (not to mention the other ecological services they provide), but there are tradeoffs, such as those between carbon sequestration and surface radiation budgets.
The point, he added, was that these advantages and tradeoffs must be considered together when crafting plans for the future.
Read more about desertification:
Australia Takes Lead on Combating Desertification
China Being Submerged in Sand: Desertification Spreads 1,300 Square Miles Per Year
TerrAfrica: Combating Desertification
"Wall of Trees" Planned to Help Stop Sahara Desert from Expanding