10 Apr 2014:
Mapping Program Helps
Cities See Money Saved by Planting Trees
New open-source software is helping cities better understand the benefits trees provide by calculating the value of the trees' ecosystem services, such as air quality improvements and CO2 storage. More than a dozen
cities have undertaken tree inventory initiatives, thanks to the OpenTreeMap software
, and residents have helped map more than 1.1 million trees worldwide. In addition to plotting a tree's location, users record its size, species, and other parameters that allow the software to calculate the tree's ecological value in terms of dollars saved through such benefits as cleaner air. San Diego's more than 340,000 mapped trees
, for example, are estimated to provide the city more than $7 million in benefits each year, including $4 million in air quality benefits and $2 million in reduced energy costs. In the coming months, the software will allow city managers to decide where to plant trees for maximum environmental benefit.
08 Apr 2014:
'Living Fences' Dramatically
Cut Livestock and Lion Killings in Tanzania
A novel, low-tech idea is helping Tanzania's lion population rebound: So-called "living fences" — which enclose livestock and are constructed of actively growing trees and chain-link fencing — have cut lion
A Masai villager installs a living fence.
attacks and retaliatory killings by more than 85 percent in the areas they've been installed, the Guardian reports
. Traditionally, the Masai have built livestock enclosures out of thorny acacia trees, but those fences are relatively fragile. Chain-link fencing alone is more durable, but leopards and small lions can scale the fences, and hyenas can tunnel in below. By interweaving actively growing African myrrh trees with the chain link fencing, the Masai have created a barrier that lions can't climb over, and their root systems prevent predators from digging under the fence. Because livestock predation has been cut, communities that had been killing six or seven lions annually now kill, on average, less than one, leading to a rebound in lion populations.
01 Apr 2014:
Delaware River Watershed
Is Focus Of Large-Scale Restoration Project
A Philadelphia foundation is providing $35 million to launch a host of programs aimed at better protecting the Delaware River
, which flows through the heart of
Delaware River at Trenton, New Jersey
the populous U.S. eastern seaboard and provides drinking water for 15 million people. The William Penn Foundation, working with nonprofit groups such as The Open Space Institute, says its Delaware River Initiative will protect more than 30,000 acres of land, launch 40 restoration projects, create incentives for businesses and landowners to protect the watershed, and set up a comprehensive program of water quality monitoring that will enable the foundation and its partners to measure the success of their programs and the overall health of the river. A cornerstone of the foundation’s initiative will be its restoration and protection work in eight so-called “sub-watersheds” that feed into the Delaware River.
24 Mar 2014:
Ride-Sharing Could Cut Taxi
Trips by 40 Percent in NYC, Analysis Shows
New interactive maps from MIT analyze the potential environmental and economic savings of ride-sharing in dense urban areas — in particular, the benefits of sharing taxicabs in New York City. The project, called
, uses data from 170 million trips made by New York City's 13,500 taxis in 2011. High-resolution GPS coordinates and timestamps for each trip allowed researchers to pinpoint locations in the city that are high-traffic hubs for taxi pick-ups and drop-offs, as well as calculate fare savings, decreases in total miles traveled, and cuts in CO2 emissions if ride-sharing existed. The researchers found that taxi-sharing could reduce the number of trips by 40 percent with only minimal inconvenience to the passengers. The findings highlight the potential benefits of ride-sharing in New York and other cities, including lower vehicle emissions, reduced congestion, and savings in time and money.
07 Mar 2014:
U.S. Car-Sharing Programs Have
Taken 500,000 Cars off Roads, Report Says
The rapid growth of car-sharing programs has cut the number of vehicles on U.S. roads by more than half a million, according to new research
by AlixPartners, a consultancy group with clients in the automotive industry. The trend will continue beyond 2020, the group projects, at which point 4 million people will be participating in car-sharing programs and 1.2 million fewer cars will be on the road. Of the 10 cities surveyed, residents of Boston, home of the Zipcar company, were most aware of car-sharing programs. Young people and, surprisingly, households with children were least likely to own their own cars, the survey said. Roughly half of the people who had tried car-sharing had already decided not to purchase or lease their own car, and did not plan to do so in the future. Rather than environmental concerns, nearly 60 percent of interviewees said cost and convenience led them to participate in car-sharing.
11 Feb 2014:
Shrinking Household Size
May Offset Progress in Curbing Population
Household size — the number of people living together under one roof — has been shrinking worldwide, and the trend could have major consequences for resource consumption
, new research finds
. Although global population growth has been somewhat curbed in the developed world, the number of households has continued to grow at a much faster pace in nearly all countries, Michigan State University researchers found. Average household size in developed nations declined from approximately five members in 1893 to 2.5 in 2000, while the rapid decline in household size in developing nations began around 1987, according to the research
, which analyzed trends between the years 1600 and 2000. Smaller households are typically less efficient, with fewer people using proportionally more land, water, and energy. Constructing housing units also consumes lumber and building supplies, and generally requires building more roads and commercial areas. "This will put enormous strain on the environmental life support system we rely on, even if we achieve a state of zero population growth," one study author said.
Photo Essay: In New Orleans, an
Architect Makes Water His Ally
Dutch Dialogues II
No city in the United States faces as grave a threat from flooding, hurricanes, and rising seas as New Orleans, part of which lies below sea level. But New Orleans architect David Waggonner
and his associates, learning lessons from the Dutch
, have proposed a revolutionary vision for New Orleans that seeks to make an asset of the water that surrounds the city, remaking unsightly canals into an important and scenic part of the landscape and mimicking nature to store rainfall. Waggoner’s firm has been chosen to help develop a Greater New Orleans Urban Water Plan
, a first step in what could be a multi-billion dollar project to redesign the ways in which the region co-exists with water. “To sustain the city in this difficult site in an era of rising seas and more extreme weather, we must convert our necessities into niceties, into desirable places that connect with people and culture,” Waggonner says. View the Photo Gallery
29 Jan 2014:
Driven by State Incentives
Electric Cars Top Vehicle Sales in Norway
Norwegians have been snapping up electric cars: In the last three months of 2013, the Tesla Model S and Nissan Leaf outsold all other cars, including conventionally fueled models. But rather than environmental concerns,
An EV charges up in Oslo
a host of government incentives — totaling an estimated $8,300 per vehicle — are largely driving the boom, the Guardian reports
. Norway, a country of only 5 million people, currently has around 21,000 electric vehicles (EVs) on the roads, compared to 70,000 EVs among 313 million Americans and 5,000 EVs among 63 million people in the UK. More than 1,200 EVs are being sold in Norway per month thanks to incentives that include free electricity for recharging, lower sales tax rates, waived tolls, free parking, insurance discounts, and permission to drive in bus lanes, which are less crowded. The EV rush is expected to slow, however, as bus lanes become more crowded, and the government plans to end financial incentives once 50,000 EVs are registered, which could occur by 2016.
07 Jan 2014:
Suburbs Offset Low Carbon
Footprints of Major U.S. Cities, Study Finds
City-dwellers in the U.S. have significantly smaller per-capita carbon footprints than their rural counterparts, according to new research
from the University of California, Berkeley. But the carbon-intense suburbs surrounding major cities essentially cancel out the small carbon footprints of city residents,
the study found. Vehicle emissions accounted for the majority of carbon dioxide produced in the suburbs, reflecting suburbanites' longer commutes to work, school, and stores. The study looked at 37 factors — including weather, income, home size, and transportation data — to estimate household carbon footprints. The average carbon footprint of households living in the center of large, densely populated cities is about 50 percent below the national average, while households in distant suburbs have carbon footprints up to twice the national average, according to the study published in Environmental Science & Technology
19 Dec 2013:
Los Angeles Becomes First
Major U.S. City to Adopt Cool Roof Rule
The Los Angeles City Council has voted unanimously to require "cool roofs" for all new and refurbished homes, becoming the first major U.S. city to do so
. "Cool roofs" incorporate light- and heat-reflecting building materials, which can lower the surface temperature of the roof by up to 50 degrees F on a hot day, according to Climate Resolve
, the local organization that pushed for the ordinance. Such roofs do not necessarily need to be white, the Global Cool Cities Alliance says; they can also be shades of gray, or even red. Research suggests that by mid-century temperatures in Los Angeles will increase by 3.7 to 5.4 degrees F, with the number of days above 95 degrees F tripling in the city's downtown. "The changes our region will face are significant, and we will have to adapt," said UCLA scientist Alex Hall, who led the research. The mandate will not cost homeowners additional money because of expanded incentives.
09 Dec 2013:
Intensifying Storms Are
Contributing To Ongoing U.S. Wetlands Loss
The U.S. is losing wetlands at a rate of 80,000 acres per year, in part because of intensifying coastal storms and sea level rise, according to a new government study
. From 2004 to 2009, the country lost more than 360,000 acres of freshwater and saltwater wetlands, a decline driven both by traditional factors, such as coastal development, as well as worsening storms and slowly rising seas, the study says. The rate of loss is a signal that government efforts to protect and restore wetlands are failing to keep pace with major environmental changes, experts told The Washington Post
. The most pronounced wetlands losses were along the Gulf of Mexico, where major hurricanes have wreaked havoc on coastal lands. Along the Atlantic coast, a rapid increase in coastal development is funneling stormwater runoff into wetlands that cannot handle it, the study said. The loss rate of 80,000 acres annually represents a 25 percent increase over the rate of wetlands loss during 1998-2004, the last time government agencies examined the problem.
06 Dec 2013:
China Doubles Pace
Of Renewable Energy Installation in 2013
Over the past 10 months China has added renewable energy sources to its power grid at double the pace of 2012, according to its National Energy Administration (NEA). The renewable energy push, part of a massive effort to cut air pollution in China's large cities, has added more than 36 gigawatts of clean energy capacity
Shanghai, Dec. 3, 2013
so far this year, Bloomberg News reports
. Hydroelectric power grew by 22.3 gigawatts in the first 10 months of 2013, new nuclear energy installations totaled 2.2 gigawatts, solar 3.6 gigawatts, wind 7.9 gigawatts. China's solar energy capacity could triple from 2012 levels to 10 gigawatts by the end of the year, while wind and nuclear power capacity could increase by 22 and 17 percent, respectively, the NEA said. That should offer some relief from China's choking air pollution. In Shanghai, schoolchildren were ordered indoors today
as air pollution reached extremely hazardous levels, exceeding World Health Organization health guidelines for fine particulate matter by 24 times.
05 Dec 2013:
Urban Car Use Declines
As Biking and Public Transit Rise in the U.S.
Americans in urban areas are driving less, biking more, owning fewer cars, and using public transportation more frequently, according to new research by the U.S. Public Interest Research Group
(U.S. PIRG). The number of people driving to work fell in 99 of 100 major urban areas between 2006 and 2011, and the number of miles driven by car fell in three-quarters of the cities studied over that time, the PIRG study showed. The proportion of people biking to work increased in 85 of 100 cities, while the number of miles traveled on public transit increased in 60 of 98 cities. Meanwhile, the number of people working from home grew in all 100 cities, the report said. From 2004 to 2012, the average number of vehicle-miles driven per person decreased by 7.6 percent nationwide. "There is a shift away from driving,” said Phineas Baxandall, an analyst for the U.S. PIRG Education Fund. "Instead of expanding new highways, our government leaders should focus on investing in public transit and biking for the future."
06 Nov 2013:
Disturbed Tropical Forests
Are Slow to Regain Plant Biodiversity
In tropical forests that are regrowing after major disturbances, the ability to store carbon recovers more quickly than plant biodiversity, researchers from the U.K. have found
. However, even after 80 years, recovering forests store less carbon than old-growth
A regrowing tropical forest in Brazil
forests, according to a study published in the Proceedings of the Royal Society B.
This is likely because regenerating forests are often dominated by small, fast-growing trees and it may take centuries for larger trees, which hold more carbon, to become established, according to scientists from the Center for Ecology & Hydrology and Bournemouth University, who studied more than 600 recovering tropical forests. Tree species that are hallmarks of old-growth forests were rare or missing in the regrowing forests, the study showed. Since regenerating forests are often located far from old-growth forests and surrounded by farmland, it may be difficult for animals to move seeds between the forests, which may account for the lower plant biodiversity, researchers said.
05 Nov 2013:
Beijing To Limit New Cars
By 40 Percent in Anti-Pollution Drive
In an effort to reduce severe air pollution in the Chinese capital, Beijing will limit by 40 percent the number of new cars sold annually for the next four years, cutting license plate allocations from 240,000 to 150,000 each
Chang'an avenue in Beijing
year. The cap, which should also help ease the capital's worsening traffic congestion, means Beijing will license only 600,000 new cars between 2014 and 2017 — fewer than in 2010 alone, Reuters reports
. By 2017, 40 percent of those licenses, which drivers vie for in auctions and lotteries, will be reserved for hybrid and electric cars. New car sales in China are currently capped in four cities — Beijing, Shanghai, Guangzhou, and Guiyang — and the government plans to limit sales in eight additional cities, the China Association of Automobile Manufacturers said.
30 Oct 2013:
Low on Natural Gas, China
Cities Will Face Choking Air Pollution
In a push to curb air pollution, China has been urging its cities to rely more heavily on natural gas and less on coal. But a shortage of natural gas is threatening that goal, as urban populations boom and domestic gas production lags, Reuters reports
. Chinese officials have said that to reduce air pollution the most densely populated parts of Beijing should use only gas heat, which limits the supply of natural gas for smaller cities and forces those cities to rely on coal. Pollution levels in Chinese cities commonly exceed World Health Organization guidelines by 40 to 50 times. The problem is most pronounced in northern China, where air pollution from burning coal has already shortened life expectancy by 5.5 years compared to the southern part of the country. China's natural gas shortage is expected to be 10 percent higher this year than last year, since more users have switched from coal. Authorities are rationing natural gas and prioritizing its use for homes and transportation, but experts don't expect the shortage to subside anytime soon.
28 Oct 2013:
Underground Heat From
Cities Could Help Power Them, Study Says
The heat generated by urban areas and their buildings, factories, sewers, and transportation systems could be used to power those cities, according to a new study by German and Swiss researchers
. Thermal energy produced by the so-called "urban heat island effect" warms shallow aquifers lying below cities, and geothermal and groundwater heat pumps could tap into those warm reservoirs to heat and cool buildings, the scientists say. In the southwest German city of Karlsruhe, the researchers found that the city of 300,000 generated 1 petajoule of heat per year — enough to heat 18,000 households. Karlsruhe's underground heat production increased by about 10 percent over the past three decades, the team reported in Environmental Science and Technology
. The biggest contributors to the city's underground heat flux were its densely populated residential areas and surface temperature increases associated with paving. Sewage pipes, underground district heating networks, and thermal waste water discharges also contribute to warming shallow aquifers, the study found.
Above a Whole Foods Market,
A Greenhouse Grows in Brooklyn
By the end of this year, a neighborhood in Brooklyn, New York, will witness the completion of a cutting-edge partnership in urban agriculture and retail — a 20,000-square-foot rooftop greenhouse built on a Whole Foods
Gotham Greens' existing greenhouse in Brooklyn.
supermarket. Atop this newly constructed store in Gowanus, Brooklyn, Gotham Greens
, a New York company that grows greenhouse vegetables, plans to grow leafy vegetables and tomatoes, which will be sold at the store below and at other Whole Food markets. Scheduled for completion in December, Gotham Greens says the new facility will be capable of producing 150 tons of produce each year, a significant increase over the capacity of the company’s existing 100-ton-per-year solar-powered rooftop greenhouse in nearby Greenpoint, Brooklyn. Read more.
15 Oct 2013:
Nine in 10 Europeans in Cities
Breathe Dangerous, Polluted Air, Study Says
More than 90 percent of Europeans living in cities are exposed to harmful levels of air pollutants, according to a new assessment
from the European Environment Agency. Concentrations of ground-level ozone, or smog,
pose a danger to 97 percent of city populations, and levels of fine particulate matter (particles with a diameter less than 2.5 microns, known as PM2.5) exceed European standards for 91 to 96 percent of city-dwellers — and European standards for both pollutants exceed World Health Organization
recommendations. A new study of European mothers linked higher PM2.5 exposure
to lower birth weight, a standard indicator of fetal development. Eastern European countries have the highest levels of PM2.5, whereas ground-level ozone is worst in northern Italy. Although emissions of most air pollutants have steadily declined over the past 10 years — lead and carbon monoxide levels, for example, now meet international standards in most areas — emissions haven't fallen as much as predicted.
11 Sep 2013:
Arsenic in Vietnam Groundwater
Slowly Moving Toward Hanoi, Study Says
As the population and water needs of Hanoi mushroom, the capital city of Vietnam is slowly drawing poisonous arsenic into the aquifer that supplies its drinking water, say researchers from the U.S. and Vietnam
. Water contaminated with arsenic has moved more than a mile
The Red River
closer to the aquifer over the last 40 to 60 years, the researchers report in Nature
, due to the city's increasing water demand; municipal pumping in Hanoi doubled between 2000 and 2010. The good news, says lead researcher Alexander van Geen of Columbia University's Lamont-Doherty Earth Observatory, is the contaminated groundwater "is not moving as fast as we had feared it might.” This will give Hanoi officials time, perhaps decades, to determine how to best deal with the problem. The study also determined why arsenic is leaching into the groundwater: As water containing arsenic mixes with high levels of organic carbon from the Red River and other surrounding aquifers, the chemistry changes and arsenic dissolves in the water.
19 Aug 2013:
Future Flood Losses
Could Increase Ten Times by 2050
The rapid growth of the world’s coastal cities, coupled with sea level rise and land subsidence, could mean that flood losses in major metropolitan areas could rise from
$6 billion in 2005 to more than $60 billion in 2050
, according to a new study. Reporting in the journal Nature Climate Change
, researchers said sea level increases of 8 to 16 inches by 2050 could cause $60 billion to $63 billion in damages in 136 of the world’s coastal cities.
That figure assumes the cities will undertake some flood control measures. Cities whose infrastructure and buildings are now most at risk — including New York; New Orleans; Miami; Guangzhou, China; and Osaka, Japan — will be joined in four decades by other rapidly growing cities,
such as Ho Chi Minh City in Vietnam and Abidjan, Ivory Coast.
Interview: Scientists, Aid Experts
Prepare for a Warmer Future
Harvard University recently sponsored a conference that brought together two groups — climate scientists and humanitarian relief workers — that will undoubtedly be collaborating more closely in the future
as natural disasters intensify in a warming world. The woman who was instrumental in opening a dialogue between these two factions was Jennifer Leaning
, the director of the FXB Center for Health and Human Rights
at the Harvard School of Public Health. In an interview with Yale Environment 360
, Leaning says the meeting underscored the huge challenges the aid community will face in a world of more extreme weather and rising seas. But at this point, she says, climate science cannot offer the specific predictions about timing or locations of climate upheaval that the aid community is seeking. “The humanitarians found that the questions they were asking were not the ones that the climate scientists were prepared to answer,” says Leaning. Read the interview
13 Aug 2013:
Too Many Urban Beehives
May Do More Harm Than Good, Experts Say
A surge in urban beekeeping may be doing more harm than good to honeybee populations
, according to UK scientists. As the number of rooftop hives increases in cities worldwide
— including London, where there are
A Berlin beekeeper
now 10 hives per square kilometer — two researchers from the University of Sussex warn that too many hives can be detrimental. Writing in The Biologist
, the magazine of the Society of Biology, they suggest that inexperienced beekeepers can create conditions in which there isn’t enough food for their insects. “If there are too many colonies in an area, then the food supply will be insufficient,” Francis Ratnieks, a professor at the university’s Laboratory of Apiculture and Social Insects, told the BBC. “This will mean that colonies do not thrive, and may also affect other species that also visit flowers.”
09 Aug 2013:
Mapping of Monarch Butterfly
Migration Yields Clues About Decline
A comprehensive mapping of the North American migration patterns of the iconic monarch butterfly
could help preserve a species threatened by loss of habitat and food sources
, a team of international
A monarch butterfly
researchers says. In a study conducted across 17 U.S. states and two Canadian provinces, from southern Texas to Alberta, biologists from Canada, the U.S., and Australia tracked the northward migration of the monarchs, documenting five generations in a single breeding season. By analyzing a chemical signature found on the adult butterflies’ wings that reveals their specific birthplace, scientists were able to track the different generations of butterflies as they migrated north to the U.S. Midwest, from which many butterflies then traveled to Alberta. According to Tyler Flockhart, a Ph. D. student at the University of Guelph in Canada and lead author of the study published in the Proceedings of the Royal Society B
, the decline in milkweed and a surge in genetically modified crops might be affecting monarch survival.
08 Aug 2013:
Conventional Hybrids Better
For Climate than EVs in Most U.S. States
Conventional gas-powered hybrid vehicles are still better for the climate than all-electric cars in most U.S. states, in part because these states still rely heavily on fossil fuels to produce electricity, according to a new report
. In 39 states, high-efficiency hybrids, such as the
Toyota Prius, produce fewer carbon emissions during their lifecycle than the least-polluting electric cars, an analysis by Climate Central found. Although an increased reliance on cleaner energy sources in some parts of the country doubled the number of states (32) where driving electric cars would be more environmentally friendly, that advantage disappeared when analysts also considered the high emissions associated with building the batteries and other components for the EVs. In 11 states, the best all-electric cars are better for the environment than gas-powered hybrids, even when manufacturing is taken into account. In 26 states, plug-in hybrid cars are the most climate-friendly vehicles, the analysis found.
11 Jul 2013:
‘Peak Oil’ Concerns Overstated
As Demand Will Fall, Study Predicts
Researchers say concerns that humanity will inevitably reach a moment of “peak oil,” which would be followed by a crippling decline in supplies, are unwarranted
because global demand for oil is approaching its own peak
. Writing in the journal Environmental Science & Technology
, researchers from Stanford University and the University of California-Santa Cruz (UCSC) say that dire projections of peak oil mistakenly assume that an increasingly wealthy planet will continue to rely heavily on oil. On the contrary, they say, the link between economic growth and oil is breaking down as a result of increased energy efficiency, lower prices for alternative fuel sources, urbanization, and limits on consumption by the wealthy. While the researchers project surging global demand for airline travel and various forms of freight transportation, there will be less reliance on oil, with conventional oil demand declining after 2035.
13 Jun 2013:
Population Could Be 11 Billion
By End of the Century, UN Report Says
United Nations report
projects that the world population could reach nearly 11 billion by 2100
, about 8 percent more than predicted just two years ago. The projected increase largely stems from the fact that the fertility rate in Africa has declined more slowly than expected, with demographers now forecasting that the number of people on the continent could nearly quadruple this century, from from about 1.1 billion today to about 4.2 billion. “The fertility decline in Africa has slowed down or stalled to a larger extent than we previously predicted, and as a result the African population will go up,” said Adrian Raftery, a professor of statistics and sociology at the University of Washington, who helped develop the statistical method used in the report. The total world population passed 7 billion in 2011. According to the new report, 8 of the top 10 increases in national populations by 2100 will occur in Africa, led by Nigeria, where the number of people is expected to jump from 184 million to 914 million.
02 Apr 2013:
Air Pollution Linked to
1.2 Million Chinese Deaths in 2010
Air pollution contributed to the premature deaths of more than 1.2 million people in China in 2010, or about 40 percent of early deaths worldwide caused by dirty air, according to a newly released analysis. The findings, based on data from a study on the distribution and causes of death globally, categorized “ambient particulate matter pollution” as the fourth-leading factor in premature deaths in China, behind dietary risks, high blood pressure, and smoking. Worldwide, air pollution was the seventh-leading cause of premature death, contributing to 3.2 million deaths, according to the study. While the study was published in The Lancet
, a UK-based medical journal, the summary of China statistics was reported at a forum in Beijing, the New York Times says
. The findings come as public outrage grows in China as residents of many cities endure choking air far in excess of safe levels.
22 Mar 2013:
Expansion of Chinese City Poses
Environmental and Safety Risks, Critics Say
An ambitious plan to expand the western Chinese city of Lanzhou into a regional industrial hub is raising concerns over what critics call lax government oversight of the environmental and safety impacts, including worries that it will siphon huge amounts of water from an already parched region
and devastate nearby mountains. Lanzhou, the capital of Gansu Province, is a city of 3.6 million and a gateway to Tibet and the Xinjiang region. It is known as one of the most polluted cities in China, and now the government is working to expand the city’s footprint by at least 70 percent, according to Caixin Online
. That expansion involves the flattening of mountaintops, and the additional 1 million people and increased industrial activity will draw water from the already polluted and over-stressed Yellow River. Opponents of the plan say buildings will also be constructed on loose soil that will be vulnerable to collapse. “It was a rash decision to begin construction on the new city before receiving environmental approvals or seeking opinions from the Lanzhou public,” said Zhao Zhong, a local activist.
20 Mar 2013:
High-Speed Trains Provide
Environmental, Social Benefits, Study Says
Bullet trains fuel real-estate booms, improve quality of life, reduce air pollution and traffic congestion, and provide a “safety valve” for crowded cities, especially in the developing world, according to a study by Chinese and U.S. economists. The study was based on China’s rapidly expanding high-speed rail network, but the researchers said the benefits experienced there would be similar for California’s proposed high-speed rail system
. Bullet train systems connecting China’s largest cities to nearby smaller cities have made these “second tier” cities more attractive for workers and alleviated traffic congestion and pollution in megacities, according to the study, carried out by economists at Tsinghua University and the University of California, Los Angeles. The study found that the trains created a new category of exurbs within 60 to 470 miles of urban centers such as Beijing, Shanghai, and Guangzhou, helping keep people from moving to already crowded megacities. The study was published in the online version of the Proceedings of the National Academy of Sciences