The NY Times continues to disorient their readers with a new Unsettled Science piece and a bit of a plug for Ronald Reagan; this time we hear from the Tree Deniers:
To Save the Planet, Don’t Plant Trees
By NADINE UNGERSEPT. 19, 2014
Apparently it is all about the albedo and the air pollution caused by, yes, trees.
NEW HAVEN — AS international leaders gather in New York next week for a United Nations climate summit, they will be preoccupied with how to tackle the rising rate of carbon emissions. To mitigate the crisis, one measure they are likely to promote is reducing deforestation and planting trees.
Deforestation accounts for about 20 percent of global emissions of carbon dioxide. The assumption is that planting trees and avoiding further deforestation provides a convenient carbon capture and storage facility on the land.
That is the conventional wisdom. But the conventional wisdom is wrong.
In reality, the cycling of carbon, energy and water between the land and the atmosphere is much more complex. Considering all the interactions, large-scale increases in forest cover can actually make global warming worse.
This is counterintuitive...
I'll say. As trees grow they act as a carbon sink but:
Besides the amount of greenhouse gases in the air, another important switch on the planetary thermostat is how much of the sun’s energy is taken up by the earth’s surface, compared to how much is reflected back to space. The dark color of trees means that they absorb more of the sun’s energy and raise the planet’s surface temperature.
Climate scientists have calculated the effect of increasing forest cover on surface temperature. Their conclusion is that planting trees in the tropics would lead to cooling, but in colder regions, it would cause warming.
In order to grow food, humans have changed about 50 percent of the earth’s surface area from native forests and grasslands to crops, pasture and wood harvest. Unfortunately, there is no scientific consensus on whether this land use has caused overall global warming or cooling. Since we don’t know that, we can’t reliably predict whether large-scale forestation would help to control the earth’s rising temperatures.
Worse, trees emit reactive volatile gases that contribute to air pollution and are hazardous to human health. These emissions are crucial to trees — to protect themselves from environmental stresses like sweltering heat and bug infestations. In summer, the eastern United States is the world’s major hot spot for volatile organic compounds (V.O.C.s) from trees.
Trees cause air pollution? Wait for it...
As these compounds mix with fossil-fuel pollution from cars and industry, an even more harmful cocktail of airborne toxic chemicals is created. President Ronald Reagan was widely ridiculed in 1981 when he said, “Trees cause more pollution than automobiles do.” He was wrong on the science — but less wrong than many assumed.
OK, I had, and have a hard time believing trees can outdo cars, but still - two plugs for Reagan in one Saturday? OK, polluting trees shouldn't be news (2003, 2004) but I try to learn something new every day.
Chemical reactions involving tree V.O.C.s produce methane and ozone, two powerful greenhouse gases, and form particles that can affect the condensation of clouds. Research by my group at the Yale School of Forestry and Environmental Studies, and by other laboratories, suggests that changes in tree V.O.C.s affect the climate on a scale similar to changes in the earth’s surface color and carbon storage capacity.
While trees provide carbon storage, forestry is not a permanent solution because trees and soil also “breathe” — that is, burn oxygen and release carbon dioxide back into the air. Eventually, all of the carbon finds its way back into the atmosphere when trees die or burn.
Interesting - if trees are burnt the sequestered carbon is back where it started in the atmosphere. But if trees rot and produce methane, that is worse in the short run, since methane is a shorter-lived but more active greenhouse gas.
The Big Finish:
Planting trees and avoiding deforestation do offer unambiguous benefits to biodiversity and many forms of life. But relying on forestry to slow or reverse global warming is another matter entirely.
The science says that spending precious dollars for climate change mitigation on forestry is high-risk: We don’t know that it would cool the planet, and we have good reason to fear it might have precisely the opposite effect. More funding for forestry might seem like a tempting easy win for the world leaders at the United Nations, but it’s a bad bet.
So much for settled science.
SINCE YOU ASK: I score it as extremely unlikely that Reagan actually said "“Trees cause more pollution than automobiles do"; I suspect that was a Ted Kennedy paraphrase. This is from the Times in 1980:
The 2004 research paper provides this Reagan quote:
Reagan said: "Approximately 80 percent of our air pollution stems from hydrocarbons released by vegetation."
At a Snopes message board I glean this:
Here's what Reagan said, in September 1980: "Approximately 80 percent of our air pollution stems from hydrocarbons released by vegetation, so let's not go overboard in setting and enforcing tough emission standards from man-made sources.''
A month later, he denied what he had said: "First of all, I didn't say 80 percent. I said 92 percent, 93 percent, pardon me. And I didn't say air pollution, I said oxides of nitrogen, And I am right. Growing and decaying vegetation in this land are responsible for 93 percent of the oxides of nitrogen.''
September 1980, above, probably ought to be August. However, Google has an archived news story that jibes with 93%:
As to the Reagan comment in the Times story that he Smoky Mountains got their name due to "oxides of nitrogen from decaying vegetation", I will say hmm; Dr. Ozone summarizes an explanation I also find elsewhere:
The Cherokee Indians referred to the Appalachian Highlands on the border between North Carolina and Tennessee as the "Place of Blue Smoke," so the Smoky Mountains probably had a blue haze long before pollution by industry and automobile exhaust. Haze is due to light scattering by very small particles. Those particles can be of natural or anthropogenic (human) origin. The Great Smoky Mountain haze was probably due to emissions of terpenes [organic compounds with formulas (C5H8)n] by trees. The terpenes may have reacted with natural levels of ozone to form light-scattering particles.
So not really oxides of nitrogen, which are no laughing matter. But as to when that science was settled and what report Reagan might have read, who knows?