More Trees, Less Global Warming, Right? -- Not Exactly

Well made point from this article is the following observation from the ecologist Ken Caldeira, co-author of this comprehensive studies on the effects of re-forestation:

"protecting the forest should be part of an effort to sustain the world's biodiversity. He also adds that the findings do not endorse clear-cutting or destroying wildlife habitats. "I think that it's important to look at preventing climate change as a means rather than an end in itself," he says. "Too narrow a focus on global warming and a loss of the broader focus of protecting life on this planet can lead to perverse outcomes." Rather than looking to forests to solve the current climate crisis by capturing carbon dioxide, he suggests targeting our "energy system," which continues to create the pollutant."

Scientists attributes the following three major functions affecting climate:

"They absorb carbon, which they pull from the atmosphere, creating a cooling effect; their dark green leaves absorb light from the sun, heating Earth's surface; and they draw water from the soil, which evaporates into the atmosphere, creating low clouds that reflect the sun's hot rays (a mechanism known as evotranspiration that also leads to cooling)."

Caldeira's studies find that these three major functions of trees "taken together created very different results in the primary latitudes studied: the equatorial tropic zone; the midlatitudes that include most of the U.S.; and the boreal areas, which are subarctic and include much of Canada, Russia and the northern extremities of the U.S."

Read the following scientific explanation given for why re-forestation may not work in every latitudes of our world preventing rapid climate warming:

In all three regions, forests dutifully perform their task of sucking carbon dioxide from the air, but light absorption and evotranspiration vary wildly. In tropical zones, forests have a significant, overall cooling effect. The soil is very wet and, so, via evotranspiration, the trees are covered by low-lying clouds that create a small albedo (power of light that is reflected by a surface). In nontropical areas, Caldeira explains, "the real significant factor is whether there's snow on the ground in the winter." If a forest covers a snowy expanse, "that has a strong warming influence," he notes, because of little cloud cover resulting from less efficiency in evaporating water. The poor cloud formation coupled with the intense absorption of light by the trees "far overwhelms the cooling influence of the carbon storage," he says.

"In midlatitudes, we got that it was basically a wash—the carbon dioxide effects were pretty much directly balanced by the physical effects," Caldeira says. He attributes this to the low contrast between light absorption from trees and from grass in pastures, though he notes that because there are some areas with wintry snow cover, the loss of a forest will probably have a slight, if any, cooling effect. He uses this example to point out the relative influence of the different forest functions. Whereas carbon levels can affect warming on a global scale, the effects of increased albedo and poor evotranspiration would affect temperatures only on a regional level. For instance, he says, "if you remove all the forest in the U.S., it would probably heat up the world, but have a slight cooling influence on the U.S., itself."

The link below will take you to the Scientific American Article:
More Trees, Less Global Warming, Right? -- Not Exactly: Scientific American

Regards,
Sohel