A future of poisoned oceans, withered crops, and irate polar bears is nobody's idea of a good time. It's clear to anyone who is paying attention that our civilization is due for an upgrade. Bright Green covers the news, ideas, opinions, and trends littering the road to an environmentally sustainable future.
This is an artist's depiction of a huge meteorite striking Earth 65 million years ago, which, scientists says, sent the dinosaurs and many other life forms into extinction. (NEWSCOM)
Protecting Earth from asteroids
Last week, a meteorite reportedly crashed through the roof of a doctor's office in Virginia. No one was hurt when, traveling at some 200 miles per hour, a half-pound space rock smashed into an examination room, breaking into pieces on the concrete floor. But the incident highlighted the not-insignificant threat posed by asteroids and ice balls from space.
The consequences of a sufficiently large asteroid or comet strike could be catastrophic, which is why you're reading this in a blog about the environment:. Depending on size, an amount of energy equivalent to tens of thousands and even many millions of nuclear bombs would be released on impact. Such a strike could be disastrous not just for civilization, but for the planet's entire web of life.
If it landed in the ocean, the impact would send walls of water in all directions, inundating continental margins. If it struck land, it could ignite continent-wide fires.
And while the destruction would be immediate around the strike zone, the problems would likely become global in the aftermath: Dust injected into the atmosphere could block sunlight. Photosynthetic organisms would stop growing. Everything else that depended on them would suffer the consequences of a reduced food supply. Mass starvation would ensue.
The last asteroid strike on this scale is widely thought to have contributed to the dinosaurs' end 65 million years ago. The asteroid, which left a 110-mile-wide crater off Mexico's Yucatan Peninsula, was only six miles in diameter, roughly the size of Manhattan Island. But three-quarters of life on Earth disappeared.
Scientists generally agree that asteroid impacts in the future are a near-certainty – smaller ones more often, larger and much more catastrophic ones less often. Scientists think that asteroids like the one that ended the dinosaurs' reign hit Earth every 100 million years or so.
That's why, in 2005, Congress mandated that NASA should try to detect 90 percent of near earth objects (NEOs) with a diameter of more 140 meters or more by 2020. Asteroids of this size hit earth roughly every 30,000 years.
Before that, in 1998, Congress asked that NASA find 90 percent of all NEOs measuring more than 1 kilometer in diameter within 10 years. These hit with less regularity, but could cause substantially more damage.
Late last week, the National Research Council released a progress report that found that NASA has been quite good at locating and tracking objects larger than 1 km in diameter. But, due to insufficient funding — only $4 million yearly for tracking NEOs — NASA wouldn't meet the goals set out by Congress in 2005.
"The current near-Earth object surveys cannot meet the goals of the 2005 George E. Brown, Jr. Near-Earth Object Survey Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020," the report states. Then the authors lay out a few options for getting the job done:
If completion of the survey as close to the original 2020 deadline as possible is considered most important, a space mission conducted in concert with observations using a suitable ground-based telescope and selected by peer-reviewed competition is the best approach. This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.
If cost conservation is deemed most important, the use of a large ground-based telescope is the best approach. Under this option, the survey could not be completed by the original 2020 deadline, but could be completed before 2030. To achieve the intended cost effectiveness, the funding to construct the telescope must come largely on the basis of non-NEO programs.
The report also calls on the US to lead the formation of an international body to monitor and deal with NEO threats.
According to experts cited by Space.com, NASA needs an additional $1 billion in funding over the next 15 years to attain its goal of cataloguing all potentially threatening asteroids. As of today, NASA's Near Earth Object Program is aware of and tracking 6,691 objects.
NASA estimates that every few million years, an asteroid comes along that could threaten civilization. Every 2,000 years, a football field-size meteor hits Earth, causing significant damage to the immediate area. Anything smaller than 25 meters will likely burn up in Earth's atmosphere.
But in 1908, something — probably a comet — exploded over the Siberia. It flattened 2,000 square kilometers (772 square miles) of forest in a largely uninhabited region.
Scientists assumed that the object was some 70 meters across. But new research indicates it might have been just 30 to 50 meters wide. And it still caused extensive damage. Objects of this size are thought to arrive every 300 years.
Because of the newfound importance of this size class, and relatively short interval at which they arrive, the authors of the report recommend that "surveys should attempt to detect as many 30- to 50-meter objects as possible."
Illustrating just how difficult asteroids are to detect, last week New Scientist reported that a 10-meter asteroid passed quite close to Earth — about one-third the distance between Earth and the moon. We noticed it only when it was three days out, far too late to head it off had it been on a collision course with Earth.
In October, an asteroid of similar size detonated over Indonesia, creating a fireball visible from the ground. Last July, an amateur Australian astronomer noticed that something had smashed into Jupiter. No one predicted it.
The good news: Our NEO detection abilities are improving. Last week, the recently launched Wide-Field Infrared Survey Explorer, which is scanning the heavens at infrared wavelengths, discovered its first near-Earth asteroid, a 1 km rock some 98 million miles away. It poses no threat to Earth — at least not on its current orbit.
Even if we saw an object headed our way with enough lead time, what could we do? The National Research Council report lists four approaches:
1. Get out of the way — evacuate of the soon-to-be-impacted area.
2. Use a "slow push" or "slow pull" exerted by spacecraft to nudge the asteroid off a collision course with Earth.
3. Fly something directly into the asteroid to change its path.
4. Detonating a nuclear device on or near the asteroid to either destroy it or move it off-course.
But for large meteors, such as the one that took out the dinosaurs, the authors acknowledge that there's currently no "feasible defense." Which doesn’t mean we can’t develop one.
The authors conclude their executive summary with an interesting discussion on the probability of catastrophes like this, and what — if anything — to do about it. The discussion echoes some arguments in the global warming debate — namely, that allocating resources now toward heading off potential catastrophes is, even if they're unlikely, a good investment if the catastrophes in question are costly enough.
[T]he committee points out a current estimate of the long-term average annual human fatality rate from impactors: slightly under 100. At first blush, one is inclined to dismiss this rate as trivial in the general scheme of things. However, one must also consider the extreme damage that could be inflicted by a single impact; this presents the classic problem of the conflict between extremely important and extremely rare. The committee considers work on this problem as insurance, with the premiums devoted wholly towards preventing the tragedy. The question then is: What is a reasonable expenditure on annual premiums?
The authors then outline three funding scenarios — $10 million, $50 million, and $250 million. The first option wouldn't be enough to achieve NASA's goals as currently state. The second option would, however. In the third scenario, NASA could achieve its goals and also provide for a space mission and real-life testing of NEO mitigation strategies.
Policymakers, the authors say, must decide which is best.
Because of the heavy wear they receive, soccer fields require more emissions-causing care than regular lawns and also trap less carbon. (NEWSCOM)
Lawns may contribute to global warming
It's the sort of headline that would grab the attention of any city dweller: Urban 'Green' Spaces May Contribute to Global Warming. As it turns out, "green spaces" doesn't mean pocket parks or wooded areas. It refers to grass. Grass in parks and grass covering athletic fields.
And, although the study – from the University of California Irvine – looked at grass in parks, the conclusions may give pause to lawn-proud homeowners, too:
Why?
It's not so much the grass -- which does remove CO2 from the air and store carbon in the soil -- but the care that the lawn needs: applying fertilizer, mowing, irrigation, leaf blowing, etc., all of which produce emissions (four times greater than the amount of carbon stored). Editor's note: Please note at the end of this post that this data is being disputed.
The two athletic fields looked at by the researchers produced even worse results than grass (which hort. and ag, scientists always refer to as "turfgrass") in picnic areas.
Soccer and baseball fields get such hard use that they're often aerated and replanted: Due "to soil disruption by tilling and resodding – they didn’t trap nearly as much carbon as ornamental grass [the grass in picnic areas] but required the same emissions-producing care," the university says.
Previous research demonstrated the carbon-storing ability of lawns, but didn't compare that to the emissions that result from grooming and other care.
All this matters because grass currently covers almost 2 percent of the land in the continental United States.
Editor's Note: On Feb. 15, we received this notice from the Outdoor Power Equipment Institute, which is excerpted:
The Outdoor Power Equipment Institute today announced that Dr. Amy Townsend-Small of University of California – Irvine (UC – Irvine) acknowledged a computation error of carbon used to maintain turf in the recently released UC-Irvine study published January 19, 2010, titled “Carbon Sequestration and Greenhouse Gas Emissions in Urban Turf.” With the error corrected, ornamental grass is in fact shown to be a net sequester of carbon even when inputs are accounted for in grass maintenance. The correction has been submitted to the American Geophysical Union (AGU) who published the paper.
Upon review of the report, various flaws were discovered, including one significant math error that was made in computing the carbon consumed during mowing. The carbon from fuel consumption was multiplied by 12, one too many times, to convert from monthly to annual data. The error was not caught during the peer review process prior to publication of the paper by the AGU. When the computation is corrected, turfgrass actually is a net sequesterer of carbon dioxide, reversing the conclusions of the original report that was widely reported in the media.
“Blaming grass for contributing to global warming is a non-starter when you look at the facts. The grass in your backyard is working hard to keep us cool, soak up carbon, capture particulates, produce oxygen, capture rain water and reduce run-off. We need to focus on the right plant in the right place and on management practices that maximize the environmental benefits potential of turfgrass,” said Kris Kiser, Executive Vice President of OPEI.
Kiser added that, “While the UC-Irvine study, rightly so, highlights that mismanagement of turfgrass can occur via excessive fertilization and irrigation, and inefficient maintenance practices, the focus should be on proper management techniques.” OPEI stressed that proper management techniques can minimize carbon emissions and maximize the benefits of carbon sequestration in turfgrass; for example, proper selection of turf based on climatic region (drought resistant species) and leaving grass clippings on the grass to serve as a natural nitrogen fertilizer.
OPEI also noted that the UC-Irvine study did not acknowledge the dramatic reductions of emissions and fuel use profile for today’s gasoline and diesel equipment, nor did the study disclose what model equipment and corresponding fuel use numbers were used.
Sheep Dog Hollow is a 1902 farmhouse in Connecticut that is being renovated with both the environment and the family budget in mind. Currently being decided: tankless water heaters or conventional ones? (Joanne Ciccarello/Staff/The Christian Science Monitor)
Tankless water heaters: pros and cons
One of the great gifts in undertaking this attempt to renovate Sheep Dog Hollow in a green and economical manner is the way the project has changed and challenged the way I think.
So many things that I used to take for granted – water, for instance, both hot in the house and cold out in the pond – I look at quite differently. I see now – in a way that I hadn’t before – that it’s imperative to protect and conserve both whenever possible to ensure that they’ll be plenty for generations to come – even if it’s going to cost me a bit more upfront. ( Continue… )
A woman carries a load of firewood in Seguin, Haiti, among a beautiful but nearly treeless landscape that is supposed to be a protected forest. Haitians use the trees as fuel either by burning them dorectly or turning them into charcoal. (NEWSCOM)
After the earthquake: Haiti's deforestation needs attention
Ever since a 7.0 magnitude earthquake hit Haiti a week ago — the most powerful to strike in 200 years — stories of the extraordinary damage and suffering wrought by the disaster have dominated airwaves and front pages around the country. The coverage and the outpouring of aid that followed have, for the time being, focused international attention on the country's poverty and vulnerability to disasters just like this, hopefully to lasting effect.
But somewhat overshadowed in all this activity is one of Haiti's longer term, but nonetheless serious, problems.
The island nation suffers from one of the highest rates of deforestation in the world. This is troubling for a number of reasons. The loss of nearly all its trees promises to amplify how dramatically earthquakes, hurricanes, and other periodic natural occurrences impact Haitians, to say nothing of deforestation's impoverishing legacy of erosion and climate change on local scale (less moisture). Without trees holding the soil in place, a heavy rain — let alone a hurricane or an earthquake — can easily cause mudslides on the island's steep slopes.
Haiti and the Dominican Republic share the same island in the Caribbean — Hispaniola. Both countries are at the same latitude and, generally speaking, the same climatic conditions prevail.
But one country, the Dominican Republic, has lush forests. The other, Haiti, is almost completely brown and bare. The stark difference is visible from high above — one side green and full of foliage, the other bare.
Here's a photo from NASA and another from a National Geographic story in the 1980s.
Fewer than 100,000 acres of forest remain in Haiti, a country that was three-quarters tree-covered when European explorers first arrived 500 years ago. The nation, the poorest in the Western Hemisphere, has lost perhaps 98 percent of its tree cover, one of the worst cases of deforestation in the world.
By most accounts, cooking fires are the major culprit behind the nation's loss of trees. Haitians use trees as fuel either by burning the wood directly, or by first turning it into charcoal in ovens. Seventy-one percent of all fuel consumed in Haiti is wood or charcoal, according to the US Agency for International Development.
Every year, the country's 9 million (and growing) inhabitants burn a quantity of wood and charcoal equal to 30 million trees, according to this essay. That's 20 million more trees than Haiti grows yearly.
The Dominican Republic largely put a halt to this practice by banning it outright, and then by subsidizing propane fuel as a substitute. According to Greenwire, however, an illegal charcoal trade is thriving along the border of the two countries. Charcoal cartels have cut down trees on the Dominican side for sale on the Haitian side. (In December, three people were killed on the Dominican side in a charcoal trade-related dispute.)
The loss of trees and their roots has led to widespread erosion. Some 36 million tons of valuable topsoil is swept away yearly, according to the United Nations. Some ends up in waterways. Silt influx has raised the level of Lac Azuei, for example, by a number of feet, reports Greenwire:
Rapid erosion caused by deforestation is spilling large quantities of silt into Lac Azuei, raising lake levels and flooding the road connecting Port-au-Prince to Malpasse. The original road already lies 2 feet below the water line, but the government has been piling sand on top of it to keep the critical passage open. The lake is rising still.
National Geographic reports that the extensive deforestation will likely exacerbate the negative impacts of the recent earthquake. When the ground moves and there's nothing holding the loose earth in place, landslides become a greater threat.
Indeed, in 2004, when a storm hit Hispaniola, the death toll was relatively low in the Dominican Republic. But in flood- and mudslide-prone Haiti, more 3,000 people died.
This Associated Press article chronicles another effect of deforestation: less moisture for growing crops. Said one farmer, “Dew allows us to grow cabbage, potatoes and beans but we can’t grow anything else anymore.”
In 2003, The Los Angeles Times faulted unregulated construction and irrigation practices for the country's erosion problem. The story also points out that 70 percent of Haitians are unemployed. For them, the charcoal trade, however environmentally damaging, is the only way to make a living.
Here's a first-person account of environmental changes in one lifetime:
I was born and grew up in a small village in southern Haiti. I thought I was living in a paradise when I was young. Although there were no angels flying around, I could see many different types of birds, within just a one-minute walk from my house I could see three flowing rivers, the mountains were green and the people had enough food to eat.
Years later, the author returns to his village. He writes:
When I visited my village in 1980 (the last time), it was all brown. No vegetation. Most of the trees I used to see as a boy had been cut down. The birds had left the village. No place to build their nests or for them to rest. No rainfall. The rivers were almost all dried out. My neighbors had moved to other areas. Some had gone to Port-au-Prince for a better life; many people I knew (young and old) had died. My village is like a desert and I believe this same dynamic has occurred in many other places in Haiti.
So what to do? A recent article suggests a few approaches. One possibility: a jatropha tree that can be converted into biofuels (no more importing diesel for electricity generation) and fuel for cooking. Another possibility, making briquettes from recycled paper for use as fuel.
But there are obviously more systemic problems. Poverty coupled with population growth are two factors driving Haiti's deforestation. If Haitians had fuel besides wood or charcoal to cook with, they'd probably use it. (This approach worked in the Dominican Republic.) If they had employment opportunities other than the charcoal trade, which supplies a meager income at best, they'd probably jump on it.
As The New York Times' Nicholas Kristof writes, there are legitimate concerns over aid dependency in Haiti, not to mention what he calls the country's "lousy" leadership and governance. But, because of its location — close to the US — Haiti should invite investment, he says. We need to "set broken bones" and "dig people out of rubble" right now, he declares, but development of the nation's infrastructure and economy is the real solution for the long term.
Editor's note: For stories, blogs, and updates on Haiti after the earthquake, go to the Monitor's Haiti topic page.
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.
At Silverio Mechanical, in Old Saybrook, Conn., Alexandra Marks and fiance, Martin Sheridan, discuss tankless water heaters for their home renovation. (Joanne Ciccarello/Staff/The Christian Science Monitor)
Are tankless water heaters worth the extra cost?
I got a call from my energetic, creative sister-in-law the other day that made me realize I’d been remiss.
“We need a new water heater,” she said. “I know you’re putting in an on-demand system at Sheep Dog, but Pete has been doing some research and he’s got some real questions about it.”
I then realized that early on in this venture in the green and, we hope, economical renovation of Sheep Dog Hollow, I concluded that we’d put in an on-demand water system and left it at that. I never gave the hot water question its own blog post, parsing the pros and cons. ( Continue… )
White-rumpled sandpiper (Calidris fuscicollis) chicks, Bylot Island, Nunavut, Canada. (Photo courtesy of Laura McKinnon)
Why birds migrate to the Arctic
Why don’t migratory birds just stay home? Why do they travel tens of thousands of miles — from the tip of South America to the Arctic, for example — and back every year?
By any measure, these trips are long, arduous, and costly. Migratory birds risk storms, predators, and fatigue, to say nothing of humans with guns. And the farther north they nest, the more it costs metabolically just to be there.
Scientists have long assumed that birds make these trips because summering grounds at the top of the world offers some advantage. Whatever the costs are, in other words, the migratory birds must be more than compensated by some quality unique to the Arctic.
Indeed, with constant sunlight fueling plant growth, the Arctic summer is notable for its explosion of life. And scientists have long thought that this abundance of resources — as well as a relative lack of competition for them — has something to do with enticing birds to (evolve to) migrate there.
The extreme environment of the far north also has fewer parasites. Traveling to environs with fewer parasites might be well worth the price of the voyage. A large parasite load can take quite a toll.
Now, a new study in the journal Science emphasizes another reason the long voyage may be worth it for birds: fewer predators.
Titled “Lower Predation Risk for Migratory Birds at High Latitudes," the study finds that, the farther north birds go in the Arctic, the lower the risk of predation. Fewer predators mean that vulnerable young have greater chance of survival. Even accounting for the huge energy cost of the long voyage, having young in the Arctic improves reproductive success.
Over the course of two summers, the researchers measured predation of 1,555 artificial nests along a 2,080-mile (3,350-kilometer) corridor between the southern part of Canada's Hudson Bay and the northern part of Ellesmere Island, which is near Greenland.
Predation risk decreased by 3.6 percent for every degree latitude between 53 degrees N. and 82 degrees N. The risk of predation was more than twice as high at the southern part of the study area compared to the northern.
“These results provide evidence that birds migrating farther north may acquire reproductive benefits in the form of lower nest predation risk,” write the authors.
An accompanying article entitled “Explaining Bird Migration” offers some context. More than anywhere else, Arctic ecosystems are shaped by predator-prey interactions, say the authors. That’s partly because there are so few species to begin with. The few species that can survive the harsh conditions — lemmings, arctic fox, and snowy owls, among others— are, by definition, major players in the ecosystem.
The relative simplicity of these ecosystems works to migrating birds’ favor — at least most of the time, the authors surmise.
Lemmings, a major prey species in the Arctic, go through three- to four-year boom and bust cycles. When lemmings abound, predators likely leave waterfowl alone. But when lemmings are scarce, predators turn to the shore birds. These authors argue, therefore, that migrating north only really works where there are lemmings to keep foxes, owls, and other predators distracted (or fed). The lemmings’ sacrifice makes the birds’ trip worthwhile.
Also in bird migration news this week, the arctic tern was crowned "king of the commuters."
"A high-tech tracking survey has revealed that the annual migration of the Arctic tern is the longest in the animal kingdom – with some birds flying the equivalent of three journeys to the moon and back over their lifetimes," reports New Scientist.
The spillway on the pond is located at the end of the dirt road. Sheep Dog Hollow farmhouse is on the same lane as the spillway. Although there's plenty of water in the area, water conservation will be a rule at Sheep Dog Hollow. (Courtesy of Mick Marsden)
Water conservation – the why and how for homeowners
At Sheep Dog Hollow, our green and economical renovation challenge, we apparently have an abundance of water. The view from almost every window includes a peek at a pond, or a brook, or one of the two lakes at either end of our dead end road. And did I mention we’re a mere four miles from the mighty Connecticut River?
A lack of water does not appear to be a problem. But that doesn’t mean that water use shouldn’t be paid proper attention in our effort to renovate in a green manner. It turns out that residential and commercial development, industry, and an a whole assortment of other human activities, such as watering the lawn, are putting a stress on the world’s water supplies – even when it’s not apparent. ( Continue… )
A recent study shows that butterflies in California are reeling from increasing development and a warmer climate. (NEWSCOM)
California butterflies having a tough time
Butterflies are among the most popular insects. Practically everyone enjoys seeing the colorful creatures flit among flowers to feed on nectar and pollen. But life isn't necessarily easy for a butterfly: Maximum expected lifespan ranges from four days to 11 months. And the Monitor recently reported that many trees in the monarch butterfly's winter home in Mexico are being killed by bark beetles.
More bad news for butterflies arrived this week from Arthur Shapiro, a professor of evolution and ecology at the University of California, Davis. Drawing on his unique 35-year database of twice-a-month observations at 10 sites at various elevations – from sea level to tree line – in north-central California, "we found many lowland species are being hit hard by the combination of warmer temperatures and habitat loss," said the butterfly expert.
The 10 survey sites lie along Interstate 80 and range from low-lying Suisun Marsh on San Francisco Bay to 9,103-foot-high Castle Peak near Donner Summit.
The analysis, to be published online this week in the journal Proceedings of the National Academy of Sciences, concludes that the number of different species of butterflies (diversity) is falling at the sea-level sites and beginning to fall at high elevations as temperatures become too warm for the butterflies that normally live there.
Only at the tree line had the number of species increased. There, "butterfly diversity is actually going up, as lower-elevation species react to the warming climate by moving upslope to higher, cooler elevations," the research team reported.
Lowland species were also being hit hard by habitat loss due to development. Losses were greatest where land was converted from rural to suburban or urban uses.
One of the most surprising findings from the analysis is that "ruderal ('weedy') butterfly species that breed on 'weedy' plants in disturbed habitats and are highly mobile are actually declining faster than 'non-weedy' species -- those that specialize in one habitat type, Dr. Shapiro said:
This is especially true in the mountains, where such species do not persist over winter but must recolonize every year from lower altitudes. As their numbers drop in the valleys, fewer are available to disperse uphill, and the rate of colonization drops.
"Butterfly folks generally consider these ruderal species to be 'junk species,' sort of the way bird watchers think of pigeons and starlings," said Shapiro. "So it came as a shock to discover that they were being hit even harder than the species that conservationists are used to thinking about.
"Some of the 'weedy' species have been touted as great success stories, in which native butterflies had successfully adapted to the changed conditions created by European colonization of California. That was the case for many decades, but habitat loss has apparently caught up with them now."
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.
The 'backyard' at Sheep Dog Hollow includes a running brook and a pond. But water conservation is still important. (Joanne Ciccarello/Staff/The Christian Science Monitor)
Water conservation: Is it necessary in the Northeast?
The presence of water was one of the many attractions of Sheep Dog Hollow, the hundred-year-old farmhouse we’re renovating in as green and economical manner as possible.
Not only did the house sit in a bucolic farm setting, surrounded by dozens of acres of land in conservation easement, but it had a pond out back that was fed by a brook, which eventually fed into a lake at the end of the dead-end road where the old house sits. Across the road runs another large brook, which feeds into yet another pond that sits at the other end of the road. ( Continue… )
A gray whale in the waters of the Bering Strait. (NEWSCOM/file)
How the Bering Strait influences Earth's climate
At 50 miles wide, the Bering Strait, which separates Alaska from Russia, hardly seems like a major player in Earth's climate.
But a new study in the journal Nature Geoscience concludes that this shallow strait between the North Pacific and the Arctic oceans has played a large role in climate fluctuations during recent ice ages. Depending on whether it's closed or open, the strait dramatically changes the distribution of heat around the planet.
When sea levels decline enough that water can no longer flow from the Pacific to the Arctic through the strait, the North Atlantic responds by growing warmer. That warmth is strong enough to melt ice sheets and temporarily reverse the glaciation of the Northern Hemisphere.
Generally, scientists think that changes in Earth's orbit around the sun have driven the repeated advance and retreat of glaciers during the Pleistocene — the period starting 2.58 million years ago and ending about 10,000 years ago.
When less sun reaches the Northern Hemisphere during summer months, winter snows don't melt. The white snow reflects more of the sun's energy back into space, further cooling the region. Glaciers form and begin creeping southward. These ice sheets, a mile or more thick in places, suck up large quantities of water.
Compared to today, sea levels dropped by as much as 400 feet during the Pleistocene.
But while glacial periods follows Earth's orbital variations quite closely — they occur very roughly on 100,000-year cycles — for the past 100,000 years or so, a shorter warming and cooling cycle has played out over the larger one.
Even as the amount of sunlight hitting the region diminished, parts of Greenland and North America warmed by nearly 3 degrees F. Glaciers then shrank and sea levels rose by up to 100 feet, only to reverse. This cycle repeated every few thousand years. Why?
The authors argue that the Bering Strait, a choke point, is the critical factor. When sea levels dropped sufficiently, dry land emerged between North America and Asia. This dam halted the flow of water from the North Pacific into the Arctic.
At present, about 800,000 cubic meters (211 million gallons) of water per second flow into the Arctic from the North Pacific. That's about 3.6 times the discharge of the Amazon, the world's largest river.
This water from the north Pacific eventually flows to the north Atlantic. Water in the north Pacific is much fresher, and therefore much lighter, than the saltier water of the North Atlantic. And the influx of freshwater into the North Atlantic impedes a process that's critical to heat distribution around the globe.
In the north Atlantic, warm water flows north from equatorial regions. As it cools between Iceland and Norway, this water sinks and, once at a certain depth, begins flowing back south.
Scientists call this conveyor-beltlike flow the "meridional overturning circulation." And it's responsible for keeping Europe balmy compared to regions at similar latitudes elsewhere.
When the overturning is impeded, however, the transport of tropical heat to high northern latitudes slows, and the north Atlantic grows colder.
In other words, freshwater flowing into the north Atlantic can bring temperatures down in the region. Conversely, lessening the flow of freshwater into the north Atlantic can cause temperatures to rise. That's what the authors of this paper say happened repeatedly during the past 100,000 years.
Here’s the cycle: Cooling brought on by changes in Earth's orbit caused glaciers to grow and sea levels to fall. Eventually, the seas dropped far enough that the Bering Strait was closed off. The flow of relatively fresh water from the north Pacific to the north Atlantic stopped, or was dramatically decreased. Without interference from this freshwater, the meridional overturning in the North Atlantic strengthened — by about 13 percent. Parts of Greenland, northeastern North America, and Europe warmed by 2.7 degrees F. Glaciers around thenNorth Atlantic then began melting.
Meanwhile, as the northward flow of water in the Pacific was stymied, temperatures there dropped by the same amount — 2.7 degrees F.
In the end, however, this warming was self-limiting. As increased warmth melted glaciers around the north Atlantic, sea levels began to rise.
Eventually they rose sufficiently to again engulf the Bering land bridge. The flow of water from the north Pacific into the Arctic resumed. The meridional overturning in the north Atlantic again weakened. And the glaciers of the Northern Hemisphere again began advancing southward.
None of this bears directly on the current trend of human-induced global warming. But it does indicate that scientists, enabled by ever-more powerful computers and more complicated — some might say "realistic" — climate models, are improving their understanding of Earth's climate system.
It also highlights an important lesson: In complex systems (Earth’s climate), seemingly small changes, such as closing the 50-mile-wide Bering Strait, can have large consequences, like temporarily reversing a hemisphere-wide cooling trend.
Or, as we talked about last week, a little warming might cause a lot more.
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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