This NASA image taken by an International Space Station crew member in November 2009 shows the setting sun through the thin line of Earth's atmosphere. (NASA/UPI/Newscom)

Bright Green fades to black

By Eoin O'Carroll, Blogger / 02.16.10

After 22 months and some 500 posts, the Bright Green blog is coming to an end.

Even though it's closing down, in many respects Bright Green was a roaring success. Back in February 2008, when I first proposed doing a daily, Web-only update on environmental topics, the Monitor was a blog-free publication. We didn't even have the technology in place to publish directly to the Web without first running content through our (very buggy and cumbersome) print publication system.

Using WordPress, a free, open-source blogging platform, we built a new Environment section, which we bolted to our existing site in a way that made our developers extremely nervous. Still, everyone liked how the new Environment site worked, so we then cloned it to create new sections for Gardening, Books, Innovation, and Politics.

The realization that we were on to something big came in early August 2008, when I wrote a post titled "Will Paris Hilton's energy plan work?" The post sat on top of Google News for more than an hour, and the resulting onslaught of traffic ended up bringing down our entire site.

After that, it was clear to everyone that blogs would play an important role in the Monitor's Web strategy.

In April 2009, as my responsibilities shifted from writing to helping the Monitor transform from a primarily dead-tree-and-ink product into a Web-centric news organization, Environment editor Judy Lowe and science writer Moises Velasquez-Manoff joined Bright Green.

For this final post, I asked each of them to list the five posts they'd written that they were most proud of. The ever-modest Judy provided only four, adding that her real joy has been in working as the blog's editor. Her four are:

Video games can be energy hogs. Three tips to cut your power bill.

Native grasses an explosive idea for cleaning contaminated soil

Decline in honeybees highlights importance of wild pollinators

Three good green reads – from rot-proof apples to a revelation about everyone's favorite reindeer

And here are Moises's five favorites:

Community based fishery management and Somali pirates

A warmer world could make current airport runways too short

Climategate, global warming, and the tree rings divergence problem

Could water scarcity cause international conflict?

Audi's 'Green Police' Super Bowl ad controversial

And, as a final bit of self-indulgence, here are my own favorite five:

Does closing roads cut delays?

Scientists admit global warming is a hoax

Report: Illicit urban chicken movement growing in US

Are climate-change deniers guilty of treason?

Are climate change deniers like creationists?

Many thanks are in order. The people who have helped make the Bright Green blog a reality are too many to name, but a few stand out.

First, I'd like to express my thanks for the Monitor's former editor, the late Richard Bergenheim, who, in February 2007 first suggested that I write a weekly news roundup about global warming, and who, a year later, signed off on creating Bright Green.

I'd also like to thank Online Editor and politics blogger Jimmy Orr for his unceasing encouragement of my work. Jimmy is a huge thrash metal fan, and the video at the end of this post is for him.

Thanks also to Christian Scripter for his long hours spent designing and assembling the original Environment site.

And thanks also to the thousands of coders in the WordPress community. We're no longer using their excellent platform, but none of this could have gotten off the ground without their efforts.

And to Monitor science writer Pete Spotts, who has repeatedly filled in as guest blogger here and who is never too busy to stop what he's doing to answer a science question. And a very big thanks to my editor, Judy Lowe, who has repeatedly made me come off sounding far more intelligent than I actually am.

Finally, and most importantly, I'd like to thank all of our readers. Your feedback – the praise, the scorn, and everything in between – has kept me far more thorough and motivated than any editor could.

Judy, Moises, and I will continue to appear in these pages, and I hope that you'll keep reading – and commenting.

–

Follow Eoin on Twitter.

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A scientist argues in a new book that life on Earth is self-destructive. (NEWSCOM)

The Medea Hypothesis: A response to the Gaia hypothesis

By Moises Velasquez-Manoff / 02.12.10

In ancient Greek mythology, Gaia is the earth-mother goddess, the deity that gives life to all others. During the 1960s, British scientist James Lovelock first formulated the Gaia hypothesis, the idea that every living thing on Earth worked in concert to keep conditions at a certain equilibrium, or homeostasis, that was optimum for life.

In other words, organic life was geoengineering, although that geoengineering was unconscious.

One example of this principle: Scientists think life has existed on Earth, a planet that's just over 4.5 billion years old, for some 3.7 billion years. During that time, the sun has grown 30 percent brighter and yet, temperatures have remained relatively stable and within a relatively narrow margin that allows water to exist in liquid form, which is critical to life on Earth.

How have these temperatures been maintained in the face of an ever-stronger Sun? One explanation: Young Earth had more greenhouse gases., but as the sun grew stronger, the amount of these heat-trapping gases in the atmosphere shrank.

That's because life, which is carbon-based, sucked them out of the atmosphere and sequestered them. The end result was a cooling tendency that perfectly balanced out the sun's growing power, canceling out what would have been a runaway warming.

Initially the source of much controversy, the Gaia hypothesis, which Lovelock and others now consider a theory — one step above hypothesis on the "it's-been-proven-scale" — has been extremely influential in earth sciences such as ecology, to say nothing of popular culture.

In the popular imagination, Gaia – the all-nurturing, all-caring mother (earth) goddess – has become something of a cliché in her own right.

But now, Peter Ward, a noted paleontologist at the University of Washington, Seattle, has put forth a compelling counter-hypothesis with an equally prestigious-sounding Greek appellation.

It's called the Medea hypothesis, and the subtitle to Dr. Ward's eponymous new book sums it up: "Is Life on Earth Ultimately Self-Destructive?"

Ward's answer to this question is, as you might guess – yes, that by its very nature, life on Earth will ultimately lead to a premature end to conditions favorable to life on Earth.

In some versions of an ancient Greek myth, Medea, wife of the Argonaut Jason, in a big contrast to mothering Gaia, kills their children out of revenge for Jason becoming enamored of someone else.

Ward's argument, which is antithetical to the Gaia hypothesis: Life will cause its own end long before our sun, which will start expanding into a red giant in about 1 billion years, begins baking the biosphere away.

Most of the book is a systematic and fascinating dismantling of the assumptions underlying Gaia hypothesis. First are Earth's five mass extinctions. Microbes, Ward says, are implicated in all but one of these die-offs, the K-T extinction thought to have been initiated by a meteor strike 65 million years ago.

The broader point: Repeatedly throughout Earth's history, organic life, in the form of anaerobic microbes that normally inhabit oxygen-starved nooks and crannies, have emerged to extinguish life. These microbes exhale hydrogen sulfide, a gas poisonous to other life forms.

The instigator in this process is often oxygen-starved seas. Stagnant, low-oxygen seas are often preceded by rapid atmospheric warming. The tipping point is 1,000 parts per million of carbon dioxide, he says.

(We've written about the end-Permian extinction 251 million years ago, the greatest of all extinctions, and one thought to have occurred in precisely this manner.)

But, this warning aside, Ward's book isn't really about human-caused global warming. It's about the long-term future of life on the planet.

Organic life has repeatedly caused the collapse of the biosphere, and on at least one occasion (snowball earth) has almost extinguished it entirely.

Consider the advent of photosynthesizing organisms more than 3 billion years ago. Oxygen, a byproduct of photosynthesis, was deadly to the other organisms living at the time. As it accumulated, it killed — another mass extinction. (Of course, atmospheric oxygen also allowed for the emergence of multicellular life and, eventually, humans.)

The major long-term problem facing life on Earth is not, Ward says, global warming, but the gradual drawdown of carbon from the atmosphere by photosynthetic organisms.

Depletion of carbon dioxide has, in the past, caused dramatic global cooling. Twice before — once 2.3 billion years ago and again 700 million years ago — photosynthetic organisms used up such a large quantity of greenhouse gases that Earth froze over — what's called "snowball earth" — nearly ending life on the third rock from the sun.

In the future, Ward says, life's hunger for carbon will inevitably lead to a paucity of what's a fundamental building block of life, adding that this is the single greatest challenge facing life on this planet.

With graphs, he illustrates the long-term decline of atmospheric carbon dioxide over the past 3.5 billion years.

In the beginning, CO2 levels were perhaps 10,000 times higher than today's. The atmosphere was maybe one-third CO2. The subsequent trend is one of decreasing CO2 until, just before humans came along, CO2 had dropped to 280 parts per million. (Now, due to human activity, it has risen to 387 ppm.)

If carbon levels fell below 10 ppm, photosynthesis would become impossible for grasses, the most efficient carbon dioxide-utilizers around. (Trees can't handle anything less than 150 ppm.) The food chain will then collapse.

Ward forecasts that, given the aforementioned trends, carbon depletion beyond this critical threshold could happen as soon as 500 million years from now, about 500 million years sooner than the enlarging sun would begin to vaporize the oceans and make Earth uninhabitable anyway.

Then he drops a doozy:

In terms of biomass — the pure weight of all things living — our planet is already past its prime anyway. From here on out, quite independent of human activity — which isn't helping, of course — there's going to be less and less life. We're on the down slope. We're on a planet already in its old age.

Before anyone gets too anxious, Ward's dates need some perspective. While it's true that life has been around quite along time, it's also true that multicellular life – from trees to jellyfish to dinosasurs and people – has been around a small portion of that, since just before the so-called Cambrian explosion about 530 million years ago.

In other words, multicellular animal life evolved in the ocean, colonized land, and become us in roughly the same amount of time that we've got left.

More perspective: The primate lineage — monkeys, apes, gibbons and lemurs — stretches back 55 to 58 million years ago, about one-ninth of what we've got left, according to his hypothesis.

Even more perspective: The most recent common ancestor of all great apes — gorillas, chimpanzees, orangutans, and us — lived 14 million year ago, one-36th of what he says remains. And the common ancestor of humans and chimpanzees, our closest existing relative, lived just over 6 million years ago, an 83rd of the time left.

Further perspective: Modern humans have existed some 200,000 years. Multiply that by 2,500 and that's what we've got left, according to Ward.

In other words, we've got some time.

And yet, it's understandable that some readers find Ward's argument depressing. At Amazon.com, one reader calls "The Medea Hypothesis" "A Dark Book for Eggheads About Biocide." The book is "Dark, Difficult, and somewhat depressing," writes another.

But Ward's purpose in writing "The Medea Hypothesis" doesn't seem to be to elicit despair.

Indeed, although it's not apparent throughout much of the book — it would have been nice had he balanced his exploration of the past with one of the future — Ward seems to be arguing in an oblique way that Homo sapiens, with our capacity to plan in advance, are not just our own best hope, but the only hope for all of life on Earth.

He's trying to emphasize the importance of our arrival on the scene not just to ourselves, which is obvious, but to the entire biosphere. In the long run — and we're talking in the very long run here — only human ingenuity will save life from a planet that's always had an expiration date anyway.

Toward the end of the book, Ward says, "There is some dark irony in what must be done. In the near term we must reduce atmospheric CO2. Then, in the long term, we must move to keep CO2 from falling too far. But with significant engineering, both are readily possible."

And so Ward brings us full circle. Life is Medean, he's argued for 140 pages, not Gaian. By its very nature, it's self-destructive. The only hope in the very long run is through human foresight and planning, to ensure continued survival.

Then, he implies, life on Earth life will have finally overcome its Medean nature. It will have become truely Gaian.

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Audi's 'Green Police' Super Bowl ad controversial

By Moises Velasquez-Manoff / 02.09.10

Perhaps you saw that ad during the Superbowl in which eco-enforcing "Green Police" seem to run a police state of sorts. They arrest a man for choosing plastic bags at the checkout counter, storm a house for a battery discarded in the garbage, and handcuff another man on his front porch in a "light bulb crackdown." He'd installed incandescent — rather than, presumably, compact fluorescent — light bulbs.

During nearly its entire one-minute duration, the ad keeps the viewer guessing as to what it's selling — until the very end when a single driver passes unmolested through an "eco-check" roadblock. (Is that an aardvark sniffing out eco-offenses, by the way?)

The car he's driving is, we learn, an Audi — the Audi A3 TDI clean diesel to be exact — a five-seater that's supposed to get 42 miles per gallon on the highway, as well as have "healthy portions of low-end torque." Green Car Journal dubbed it the "green car of the year."

The ad, which elicited glee or despair – depending on where one falls on the "people-are-degrading-the-environment" spectrum – has generated substantial buzz on the Internet not least because of its ambiguity.

It serves as a nice litmus test of — well, something that’s not entirely clear, but which echoes sentiments often voiced in discussions around environmental degradation and human-caused climate change.

Audi's eco-friendly alternate universe looks rather Orwellian, with checkpoints, raids (one man is pulled out of a hot tub; at 105 degrees, the temperature was too high), and constant intrusion into people's private lives — a kind of libertarian nightmare.

The sole character who gets off easy in this world is the guy with the "greenest car" (manufactured by you-know-who).

But — and here viewer confusion seems unavoidable — who wants to be a winner in this universe? As Groucho Marx once said, "I don't care to belong to any club that will have me as a member." In other words, thanks, but no thanks. That's one in-crowd we'd rather not be in with.

 And that's why many, although not all, who lean greenward seem to dislike the commercial.

Of the ad, The New York Times says, "This misguided spot put the 'mental' in 'environmental."

One commenter at Discover says, "Green, yet it mocks the environmental movement. I don’t get it."

Another, this one at the NFL site, takes it literally — and is afraid: "This is by far the scariest commercial I’ve ever seen! This is not just a commercial. Its every liberal’s and Hippie’s ... dream."

A blogger at Get Energy Smart Now!, meanwhile, calls it "The Most Environmentally Unfriendly Super Bowl Ad." The soundtrack to the commercial — "Green Police" — is a reworked song by rock band Cheap Trick, originally titled "Dream Police."

The blogger then points out that "Green Police" was a term used for uniformed Nazi police (Ordnungspolizei or Grüne Polizei) in Nazi Germany:

At the very least, the indictment proves wrong a forecast made in late January by the online publication Daily Finance. Said the paper: "it's certainly never fortuitous for a German company to bring up reminders of the Third Reich. ... Still, it's likely that most U.S. viewers won't connect the 'Green Police' in their history books with the ones in Audi's Super Bowl Ad."

Grist has a slightly more nuanced take on the ad. "At first blush this seems like more teabagging -- appealing to angry white men with the same old stereotype of environmentalists as meddling do-gooders obsessed with picayune behavioral sins," says David Roberts

But after considering that interpretation, he rejects it, concluding, "The ad only makes sense if it's aimed at people who acknowledge the moral authority of the green police -- people who may find those obligations tiresome and constraining on occasion, who only fitfully meet them, who may be annoyed by sticklers and naggers, but who recognize that living more sustainably is in fact the moral thing to do. This basically describes every guy I know."

Mr. Roberts then points out that everyone arrested in the commercial is a man. (I'll add that all offenders are also Caucasian. At least one green policeman, on the other hand, is African-American. But that's it for diversity in this eco-fascist world.)

Is the gender-skewing significant? Roberts thinks so. Middle-class males are Audi's target demographic, he says. The message to that demographic: "Here's a way to meet your green obligations and still have a ["mean"] car! The Audi A3 is both green and desirable -- indeed more desirable because it's green. Buried deep in this ad, in other words, is a bright green message: prosperity, pleasure, and sustainability can be achieved together."

Those at This Dish is Vegetarian, meanwhile, take the commercial more at (a certain) face value.

"Kudos to Audi for addressing an important issue with a sense of humor rather than the standard doomsday scenario that is typically associated with the Green movement," they say.

Editor's Note: The Monitor's Environment section has a new URL. And there's also a new URL for our Bright Green blog. We hope you'll bookmark these and visit often.

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Annapurna South at sunrise, Nepal. There's disagreement among scientists about how much Himalayan glaciers are melting and the cause. (NEWSCOM)

What's really causing Himalayan glaciers to melt?

By Moises Velasquez-Manoff / 02.08.10

Two weeks ago, it emerged that the UN's Intergovernmental Panel on Climate Change had made a mistake. The IPCC's last report, completed in 2007, had forecast that, given the current rate of global warming, Himalayan glaciers would "very likely" disappear by 2035.

This date, it turns out, wasn't based on a study appearing in a peer-reviewed science journal, but on an article published in the popular science magazine New Scientist a decade ago. The article apparently misquoted Indian glaciologist Syed Iqbal Hasnain.

Hasnain has said that he noted the error when it first appeared in print all those years ago, but never contacted the magazine about correcting it. How an article in the popular press made it into the pool of studies considered by the IPCC — the panel says it focuses on peer-reviewed studies — remains something of a mystery.

But, it should be noted, the erroneous estimate did not make it into the guide for policymakers. It appears only in the full report. So what about those glaciers?

Although there's still disagreement on how much Himalayan glaciers, sometimes called "the third polar region," are melting (see Monitor colleague Ben Arnoldy's story on the difficulties of studying ice in the volatile region) glaciologists tend to agree that they are melting, and that this poses a significant problem in the long run.

More than a billion people in Asia rely on glacial meltwater for a steady, year-round supply of fresh water. If the glaciers disappear, the region's water supply might be threatened.

Now, a new study by scientists at the Lawrence Berkeley National Laboratory, NASA's Goddard Institute for Space Studies, and NCAR, finds that human-emitted aerosols are the single major contributor to glacial melt in the Himalayas.

In this case, increasing concentrations of carbon dioxide are not melting the mountain glaciers, say the authors. Particulate matter, particularly black carbon from cooking fires and coal-fired plants in India, is the real culprit.

These particulates can melt ice in two ways. First, floating in the air, they absorb sunlight and heat the surrounding atmosphere. Warmer air melts glaciers and changes precipitation patters.

In fact, weather stations across India measured a decrease in sunlight reaching the ground of about 0.5 watts per square meter per year between 1964 to 1990. After 1990, that rate of decrease went up to 1.1 watts per square meter per year.

Particulates can also melt the ice when they precipitate out of the air and land on it. Snow and ice normally reflects much of the sun's energy — up to 90 percent — back the way it came. But a layer of soot on top of the ice will absorb the sunlight, warm the ice beneath, and melt it.

The current study, which appears in the journal Atmospheric Chemistry and Physics, finds that 90 percent of observed Himalayan glacial loss in recent decades is from aerosols. Black carbon soot alone, which occurs when combustion is incomplete, is responsible for 30 percent of that melt.

The amount of soot in the air has increased substantially in the area.

Between 1990 and 2000, black carbon emissions from India increased by 46 percent, say the authors. They increased by another 51 percent in the past decade.

According the National Snow and Ice Data Center, while some parts of the Himalayas have actually seen an increase in snow in recent decades, a large swath of the Himalayas has seen a decrease of about 16 percent in the same period.

The authors propose that the increases in snow in some regions is also an effect of black carbon — specifically, it heats the atmosphere, increases upward movement, or convection, of air, and that alters precipitation patterns. Rain and snow decrease in some areas and increase in others.

The good news is, while CO2 stays in the atmosphere for a century, black carbon lingers for a much shorter time. So if most of the Himalayan glacial melt observed in recent decades is due to not to increases in carbon dioxide but to more particulate pollution, then it can be much more easily addressed, at least theoretically: Simply burn coal and biomass more cleanly.

How difficult this may be to achieve is, of course, another story.

Editor's Note: The Monitor's Environment section has a new URL. And there's also a new URL for our Bright Green blog. We hope you'll bookmark these and visit often.

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In this Feb. 14, 1981, photo, Todd Domboski of Centralia, Pa., looks over a barricade at the hole he fell through just hours before this photo was taken in Centralia, Pa. The hole was caused by a mine fire that had been burning beneath the town since 1962, and it still burns today. (AP/File)

Centralia, Pa.: How an underground coal fire erased a town

By Eoin O'Carroll, Blogger / 02.05.10

If officials in Pennsylvania's capital, Harrisburg, have their way, the borough of Centralia, Pa., will soon cease to exist.

There's not much left of the northeastern Pennsylvania coal town these days. Even in the early 1980s, some two decades after the underground fires began, more than a thousand people called Centralia home. But as the poisonous gases continued to seep from fissures in the ground, and as the sudden sinkholes threatened to cast people into the smoldering depths, the town emptied out.

Today, fewer than a dozen people remain.

Now the state wants those last holdouts gone. As the Associated Press's Michael Rubinkam reports, state officials have ordered Centralia's remaining residents to leave so that their homes can be demolished.

Nobody really knows exactly what started the fire, which began at a town dump in 1962. The burning trash ignited an exposed coal seam, and the fires seeped into the labyrinth of tunnels and shafts below. Over the next two decades, firefighters tried eight times to douse the subterranean blaze, but the fire always seemed to be several steps ahead of them. Eventually, they gave up. Extinguishing the fire would be too expensive, and anyway it didn't seem to pose too much danger.

In the early years of the fire, Centralians enjoyed not having to shovel their sidewalks and being able to harvest tomatoes from the warm ground in midwinter, Smithsonian magazine notes. But then, as the ground below turned to ash, the pavement started to buckle. The trees started dying. People started passing out in their homes from the toxic fumes.

Centralia's moment of clarity came in 1981, when the ground beneath 12-year-old Todd Domboski opened up. Todd, who had been cutting through a resident's yard, saved himself from plunging into the toxic inferno below by clinging to a tree root until a cousin rescued him.

Two years later, Congress appropriated $42 million to buy and demolish every home in the town. By 1990, only 63 people remained. In 2002, the US Postal Service eliminated Centralia's ZIP Code.

Still, a few diehards remained, squatting in houses they no longer own after the government seized them through eminent domain in the early 1990s. Some claim that the whole thing is a plot to seize mineral rights.

As the Monitor's Carmen Sisson noted in 2006, Centralia's mammoth deposits of anthracite, which once promised limitless prosperity, are now expected to burn for another 250 years.

Today, the town is not so much of a ghost town as it is a big open space with a grid of empty streets. The homes have been demolished, the rubble cleared, and the driveways now lead to nowhere.

As the AP's Michael Rubinkam notes, it didn't have to be this way. Had town officials taken swift action back when they first became aware of it, Centralia could still exist.

Half-measures. Complacence. Conspiracy theories. Denial. These themes are familiar to anyone who follows environmental topics. As Centralia is deleted from Pennsylvania's official registers, we can only hope that the name will remain in our minds as a lesson about how creeping, incremental threats can, if ignored, destroy the very ground ground beneath our feet.

Follow Eoin on Twitter.

Editor's Note: The Monitor's Environment section has a new URL. And there's also a new URL for our Bright Green blog. We hope you'll bookmark these and visit often.

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Tony Silverio, who is installing the plumbing at Sheep Dog Hollow (a 1902 farmhouse that's being renovated) is a fan of Toto toilets because of their ecologically sound low-flow flushing prowess. (Joanne Ciccarello/Staff/The Christian Science Monitor)

Low-flow toilets have improved

By Alexandra Marks / 02.05.10

To be frank, I’ve never thought much about toilets. In the past, whenever I’ve found myself in the market for a new john, the only thing that concerned me was its exterior design. I like things that are elegant and old (or, at least, that have that authentic antique look.)

But now in my effort to become a better human being, as well as renovate Sheep Dog Hollow in as green and economical manner as possible, I’ve become immersed the history and recent technological advances of the toilet. (For instance, did you know the derivation of the word? It’s from the word toile: “French for ‘cloth’ draped over a lady or gentleman's shoulders whilst their hair was being dressed, and then … by extension … the whole complex of operations of hairdressing and body care that centered at a dressing table.” ( Continue… )

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Tony Silverio of Silverio Mechanical installs the pipes for plumbing at Sheep Dog Hollow, an old farmhouse that's being renovated. (Joanne Ciccarello/Staff/The Christian Science Monitor)

The delicate toilet question

By Alexandra Marks / 02.02.10

Few people enjoy chatting casually about the bathroom, let alone about toilets. But since they’re responsible for as much as 40 percent of the water consumed inside most households, and water is becoming an increasingly precious resource, it's time to talk toilets here at Sheep Dog Hollow.

(For new readers, Sheep Dog is the 100-year-old farmhouse that we’re attempting to renovate in a green and economical manner. For our regular readers, please forgive the repetition.)

Now I confess that I stole the “talk toilets” line from a Sierra Club website, which has a delightful post that starts right up front: “Let’s talk toilets…” (Writing for the highly respected, very proper Monitor, I figured I had to get to the point in a more refined, less direct manner.)

Among other things, the post notes that “The U.S. Government Accountability Office reports that water managers in 36 states expect water shortages in the next 10 years, even under normal, non-drought conditions.” ( Continue… )

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Airplane contrails above a lighthouse. Scientists have been studying whether contrails warm or cool temperatures. (NEWSCOM)

Airplane contrails and their effect on temperatures

By Moises Velasquez-Manoff / 02.01.10

Maybe you did some airplane travel over the holidays, and maybe, once your plane reached cruising altitude, you noticed the vapor trails from other jetliners crisscrossing your path. Or possibly one day recently, you simply looked up and noticed many thin, white clouds crisscrossing the sky.

These are contrails, perhaps one of the most directly observable ways human activity can change the weather. They form when, as exhaust spews from jet engines, moisture condenses on particles of soot in the subfreezing air.

They usually appear above 26,000 feet where the air is less than -40 C (also -40 F.) But factors besides altitude also play a role in their formation. Depending on how much moisture is in air, for example, contrails last shorter or longer. Moisture availability also dictates whether they form at all, and how much they grow after formation.

As it turns out, they also impact temperatures at Earth's surface, although by how much and in which direction — up or down — is still being worked out.

Initially, scientists thought that contrails, like the naturally occurring cirrus clouds they resemble and sometimes seed, had an overall warming effect. Although contrails clearly reflected incoming sunlight, they also trapped heat from below that would otherwise escape into space. Scientists therefore thought contrails had a net warming effect.

Then Sept. 11, 2001 presented a unique opportunity to study what the sky looked like without airplanes and contrails. In the wake of the 9-11 terrorist attacks, the FAA prohibited commercial aviation over the United States for three days. That's when David Travis, an atmospheric scientist at the University of Wisconsin, Whitewater, thought to look at how temperatures might differ at temperature stations around the country.

He found that [PDF], for those three days, the average range between highs and lows at more than 4,000 weather stations across the US was 1 degree C wider than normal. In other words, contrails seemed to raise nighttime temperatures and lower daytimes ones.

But the real effect was in daytime highs, which were much higher. That would seem to indicate that, contrary to prevailing thinking, contrails might have a net cooling effect.

Certain areas seemed particularly sensitive to the absence of contrails. Because of unique climatic conditions in the atmosphere in these regions — chiefly, moisture-laden air — the Pacific Northwest and the Midwest are often covered by contrails. But when planes stopped flying right after 9-11, Travis also found that these areas saw the most dramatic increase in daytime highs.

Some have suggested that these results were skewed because unusually clear weather prevailed that week in September 2001. In other words, it was natural variation, not the absence of contrails, that led to the large temperature differential immediately following 9-11.

But there's no doubt that whether the net effect is to cool or warm, contrails can quite dramatically change cloud cover.

Immediately after 9-11, other scientists looked at contrails left by military planes, the only aircraft allowed to fly. They noticed that when planes flew in a cloudless area west of Washington D.C., within just a few hours, contrails that had begun as vapor trails just a few meters in width covered 20,000 square kilometers (7,722 square miles).

A 2006 study published in Nature, meanwhile, provided more details. The authors concluded that when a contrail forms — day or night, for example — determines whether the net effect will be warming or cooling. (Here's Scientific American's write-up [PDF] of the article.

Planes flying between 6 p.m. and 6 a.m. comprised only one-quarter of total flights examined. But they were responsible for 60 to 80 percent of contrails' warming effect ontemperatures. That's because contrails at night trap outgoing heat radiation.

Contrails during the day, meanwhile, offset their heat-trapping effect by reflecting incoming sunlight. Likewise, winter flights, which account for only 22 percent of annual air traffic, were nonetheless responsible for half the warming by contrails.

"[F]light rescheduling could help to minimize the climate impact of aviation," conclude the authors.

Or, as the Scientific American article puts it, "Kiss the red-eye good-bye."

Of course, aviation's real impact on climate probably has nothing to do with contrails. In 2005, NASA's James Hansen published a study to that effect. He found that, even if the number of contrails were quintupled, global mean temperature would increase by just 0.03 degrees C (0.05 degrees F.). Aviation emissions, which are rising dramatically, are the true culprit.

According to this Wired story, aviation is on track to have a 1.5 billion-ton carbon footprint by 2025. The entire 27-nation, 457-million-person European Union emits some 3.1 billion tons of CO2 yearly at this point.

And yet, although the net impact of contrails may pale in comparison to the net impact of carbon emissions, engineers are already thinking up solutions to contrail formation. One has proposed a powerful microwave beam mounted on the jet engine. The idea: Evaporate the condensing water and soot particles before they become contrails.

Scientist Frank Noppel, who's researching this idea, says the job would cost just 0.1 percent of a jet engine's power. Sound crazy to have a microwave pointing back the way you came? Rolls-Royce has reportedly filed a patent on the technology.

Editor's Note: The Monitor's Environment section has a new URL. And there's also a new URL for our Bright Green blog. We hope you'll bookmark these and visit often.

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After a debate about what kind of roof to put on Sheep Dog Hollow, a 1902 farmhouse that's being renovated, a cedar shake roof was installed. But it developed a problem. What now? (Joanne Ciccarello/Staff/The Christian Science Monitor)

What to do when the new shake roof buckles?

By Alexandra Marks / 01.28.10

So far Martin and I have been extremely fortunate in our attempt to renovate Sheep Dog Hollow in as green and economical manner as possible. While the 100-year-old farmhouse has needed a complete overhaul – from its once impressive granite foundation to its crumbling roof – we’ve been blessed to work with capable carpenters and masons who’ve dealt quickly with whatever problem the old house has thrown up at them. And there have been plenty.

That said, we’ve been spared the harrowing scenarios that can be found with a quick Google of “home renovation nightmares.”

But now we have a problem, and a serious one. The new cedar shake roof that was finally put on in the past two weeks has buckled after the first serious rain. And not just a little. ( Continue… )

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