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This week on "Our World" ... How forests influence Earth's climate ... A novel way to help purify drinking water ... and some facts about glaucoma, the "sneak thief of sight" ...
FRIEDMAN: "It's a challenge making the decision on whether to operate or treat with medicines and lasers, and it's a big challenge in developing countries, where there may not be as easy access to either."
Those stories, a puzzling threat to commercial honey bee hives, and more. I'm Art Chimes. Welcome to VOA's science and technology magazine, "Our World."
The respected journal devotes a good chunk of this week's issue to a special section called "Forests in Flux."
Forests cover about 30 percent of the Earth's land area, and they play a major role in the planet's climate.
The seven articles look at the forests of the past, managing forests to reduce the impact of climate change, and other topics. We spoke with authors of two of the papers.
We'll hear from Robin Chazdon, who wrote about forest restoration, in a moment.
But first, there's the question of how forests affect climate. The answer is, in a number of ways. And different kinds of forests affect climate differently.
Gordon Bonan of the National Center for Atmospheric Research in Colorado says there is a scientific consensus that human activity is contributing to global warming.
BONAN: "But what we don't know yet is how forests, and changes in forests as climate changes, will feed back to affect climate. In some cases that can be a benefit to us and mitigate climate change. In other cases it could be to the detriment and actually accentuate the climate change."
For one, forests serve as reservoirs of carbon. Growing plants take in carbon dioxide, which is a greenhouse gas. When they die, they release the carbon — slowly as they rot, or quickly if they're burned.
Another way forests affect climate is through evaporation, which can have a cooling effect.
A third process has to do with albedo — how reflective the land is. Forest-covered land is generally darker than barren land, so it absorbs solar radiation.
It gets more complicated, still. A tropical forest is different from a temperate forest, and boreal forests, found at higher latitudes, are different still. Each influences climate in different ways. The biggest impact, Bonan says, comes from the tropical and boreal forests.
BONAN: "The boreal forest has a large impact on climate because of its low surface albedo. And this keeps the climate warmer than if the trees weren't present. In the tropics, we know that the tropical forests are absorbing carbon from the atmosphere, and that deforestation of tropical forests releases that carbon to the atmosphere. These two forests are actually very important to the climate, but for different reasons."
Forests have traditionally been valued for their biodiversity, as a source of wood products, in helping maintain water quality, for their recreational and even their spiritual value. But Gordon Bonan of the National Center for Atmospheric Research says their role in managing climate has not been appreciated, especially by non-specialists.
BONAN: "And so as we begin to think about crafting policies to mitigate climate change, we need to better understand what forests do to the climate and how to manage them."
One part of forest management involves restoration after they've been damaged or destroyed, whether by nature or by people. Robin Chazdon of the University of Connecticut writes about that in her paper in .
CHAZDON: "We have depleted long-term sources of carbon. We need to really put them back. And the only way to do that is to allow slow-growing trees to accumulate carbon over time in their tissues and to keep that stored in their tissues. Those trees are also putting a lot of carbon back into the soil, and soil is a huge reservoir of carbon. And we need to really think long-term about this in terms of trying to counter carbon losses in the planet."
But she cautions that not all forests are the same. Single-crop plantations are no substitute for diverse natural forests. And Chazdon says even thoughtful and well-intentioned reforestation programs can come up short.
CHAZDON: "I think that there's a lot of promise in restoring forests, but I would caution that we can not really bring back the original forests. The types of forests that are being destroyed have developed over hundreds or thousands of years in some cases. And we can't, in the blink of an eye recreate that kind of diversity and stature."