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CU study: Little Ice Age caused by four massive volcanoes
Jan 30th
New CU-led study may answer long-standing
questions about enigmatic Little Ice Age
A new University of Colorado Boulder-led study appears to answer contentious questions about the onset and cause of Earth’s Little Ice Age, a period of cooling temperatures that began after the Middle Ages and lasted into the late 19th century.
According to the new study, the Little Ice Age began abruptly between A.D. 1275 and 1300, triggered by repeated, explosive volcanism and sustained by a self- perpetuating sea ice-ocean feedback system in the North Atlantic Ocean, according to CU-Boulder Professor Gifford Miller, who led the study. The primary evidence comes from radiocarbon dates from dead vegetation emerging from rapidly melting icecaps on Baffin Island in the Canadian Arctic, combined with ice and sediment core data from the poles and Iceland and from sea ice climate model simulations, said Miller.
While scientific estimates regarding the onset of the Little Ice Age range from the 13th century to the 16th century, there is little consensus, said Miller. There is evidence the Little Ice Age affected places as far away as South America and China, although it was particularly evident in northern Europe. Advancing glaciers in mountain valleys destroyed towns, and famous paintings from the period depict people ice skating on the Thames River in London and canals in the Netherlands, waterways that were ice-free in winter before and after the Little Ice Age.
“The dominant way scientists have defined the Little Ice Age is by the expansion of big valley glaciers in the Alps and in Norway,” said Miller. “But the time it took for European glaciers to advance far enough to demolish villages would have been long after the onset of the cold period,” said Miller, a fellow at CU’s Institute of Arctic and Alpine Research.
Most scientists think the Little Ice Age was caused either by decreased summer solar radiation, erupting volcanoes that cooled the planet by ejecting shiny aerosol particles that reflected sunlight back into space, or a combination of both, said Miller.
The new study suggests that the onset of the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions. Climate models used in the new study showed that the persistence of cold summers following the eruptions is best explained by a sea ice-ocean feedback system originating in the North Atlantic Ocean.
“This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,” said Miller. “We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time. If the climate system is hit again and again by cold conditions over a relatively short period — in this case, from volcanic eruptions — there appears to be a cumulative cooling effect.”
A paper on the subject is being published Jan. 31 in Geophysical Research Letters, a publication of the American Geophysical Union. The paper was authored by scientists and students from CU-Boulder, the National Center for Atmospheric Research in Boulder, the University of Iceland, the University of California, Irvine, and the University of Edinburgh in Scotland. The study was funded in part by the National Science Foundation and the Icelandic Science Foundation.
As part of the study, Miller and his colleagues radiocarbon-dated roughly 150 samples of dead plant material with roots intact collected from beneath receding ice margins of ice caps on Baffin Island. There was a large cluster of “kill dates” between A.D. 1275 and 1300, indicating the plants had been frozen and engulfed by ice during a relatively sudden event.
Both low-lying and higher altitude plants all died at roughly the same time, indicating the onset of the Little Ice Age on Baffin Island — the fifth largest island in the world — was abrupt. The team saw a second spike in plant kill dates at about A.D. 1450, indicating the quick onset of a second major cooling event.
To broaden the study, the team analyzed sediment cores from a glacial lake linked to the 367-square-mile Langjökull ice cap in the central highlands of Iceland that reaches nearly a mile high. The annual layers in the cores — which can be reliably dated by using tephra deposits from known historic volcanic eruptions on Iceland going back more than 1,000 years — suddenly became thicker in the late 13th century and again in the 15th century due to increased erosion caused by the expansion of the ice cap as the climate cooled, he said.
“That showed us the signal we got from Baffin Island was not just a local signal, it was a North Atlantic signal,” said Miller. “This gave us a great deal more confidence that there was a major perturbation to the Northern Hemisphere climate near the end of the 13th century.” Average summer temperatures in the Northern Hemisphere did not return to those of the Middle Ages until the 20th century, and the temperatures of the Middle Ages are now exceeded in many areas, he said.
The team used the NCAR-based Community Climate System Model to test the effects of volcanic cooling on Arctic sea ice extent and mass. The model, which simulated various sea ice conditions from about A.D. 1150-1700, showed several large, closely spaced eruptions could have cooled the Northern Hemisphere enough to trigger Arctic sea ice growth.
The models showed sustained cooling from volcanoes would have sent some of the expanding Arctic sea ice down along the eastern coast of Greenland until it eventually melted in the North Atlantic. Since sea ice contains almost no salt, when it melted the surface water became less dense, preventing it from mixing with deeper North Atlantic water. This weakened heat transport back to the Arctic and creating a self-sustaining feedback system on the sea ice long after the effects of the volcanic aerosols subsided, he said.
“Our simulations showed that the volcanic eruptions may have had a profound cooling effect,” says NCAR scientist Bette Otto-Bliesner, a co-author of the study. “The eruptions could have triggered a chain reaction, affecting sea ice and ocean currents in a way that lowered temperatures for centuries.”
The researchers set the solar radiation at a constant level in the climate models, and Miller said the Little Ice Age likely would have occurred without decreased summer solar radiation at the time. “Estimates of the sun’s variability over time are getting smaller, it’s now thought by some scientists to have varied little more in the last millennia than during a standard 11-year solar cycle,” he said.
One of the primary questions pertaining to the Little Ice Age is how unusual the warming of Earth is today, he said. A previous study led by Miller in 2008 on Baffin Island indicated temperatures today are the warmest in at least 2,000 years.
Other co-authors on the paper include CU-Boulder’s Yafang Zhong, Darren Larsen, Kurt Refsnider, Scott Lehman and Chance Anderson, NCAR’s Marika Holland and David Bailey, the University of Iceland’s Áslaug Geirsdóttir, Helgi Bjornsson and Darren Larsen, UC-Irvine’s John Southon and the University of Edinburgh’s Thorvaldur Thordarson. Larsen is doctoral student jointly at CU-Boulder and the University of Iceland.
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Boulder County has teen jobs next summer
Jan 30th
Teens, adults can now apply for Youth Corps summer jobs
Boulder County, Colo. – Boulder County residents ages 14-17 can now apply for summer jobs with the Boulder County Youth Corps. The program is also hiring adults to be Team Leaders and is especially in need of female corps members and leaders.
The deadline to submit youth applications is Friday, March 30. Other positions are open until filled.
The Youth Corps will hire up to 160 teenagers to work 30 hours per week, Monday through Thursday, from June 18 to Aug. 8 on a variety of community service projects. Team leaders will be employed from June 6 to Aug. 10 to work up to 40 hours per week, Monday through Friday.
Projects include forest thinning, historic preservation, construction and repair of fencing, trail maintenance, removal of Russian olive trees and noxious weeds, landscaping and replacing light bulbs with compact fluorescents. Youth Corps teams work in unincorporated Boulder County as well as in Lafayette, Longmont and Superior.
Applications are available at www.bouldercounty.org/youthcorps and can also be picked up at counseling offices in Boulder Valley and St. Vrain Valley schools, city and town personnel offices, most local recreation and youth centers and libraries, and at the Boulder County Human Resources office at 2025 14th St. in Boulder.
This year, corps members will earn a starting wage of $7.64 per hour, with the possibility of earning a $100 bonus at the end of the program based on merit and strong attendance. Teens who have worked for the corps in past years can earn up to $8.14 an hour. In addition, corps members are eligible for reimbursement for the purchase of work boots and gloves. RTD bus passes for the purpose of traveling to and from centralized work meeting places may be subsidized.
Team Leaders must be high school graduates, at least 21 years old, and have two years of college coursework or more, and Assistant Team Leaders must be high school graduates and at least 18 years old, among other qualifications. A full list of qualifications is available at www.bouldercounty.org/youthcorps. Team Leaders start at $13 per hour and Assistant Team Leaders at $11 an hour.
The Youth Corps offers one of the best first job opportunities available in Boulder County. Teams have completed projects such as building the new Fourmile Trail connector at Betasso Preserve Open Space and preserving the historically significant lower barn at Walker Ranch Open Space.
- Building trails is just one of many outdoor tasks Job Corps teen undertake
Boulder approves “incentive” for another innovative energy companyy
Jan 27th
City Manager approves business incentive for Eetrex
City Manager Jane S. Brautigam has approved a flexible rebate application for Boulder-based Eetrex Incorporated, for up to $26,000 in rebates. The rebates were authorized for sales and use taxes, and permit-related fees.
The flexible rebate program is one of the city’s business incentives, covering a wide range of fees, equipment and construction use taxes. Under this program, the city manager may consider a specific incentive package for tax and fee rebates to meet a company’s specific needs. The company is then eligible for the rebate after it has made its investment and paid the taxes or fees to the city.
“Eetrex is part of the new energy economy and is leading innovation in power electronics and battery systems,” Brautigam said. “The city is pleased that its incentives are helping Eetrex grow and stay in Boulder.”

Employees of the Eetrex Corporarion
Eetrex develops power electronics and battery systems for the electric and plug-in hybrid-electric vehicles, telecommunications, and computing industries. The company is also the leading developer of on-vehicle inverter-chargers, known as Invergers™. Its battery systems are being used in demonstration projects to show how they can effectively store energy from wind and solar generation to offset peak loads and utilize clean energy more effectively. In 2006, Eetrex was founded in Boulder and moved into a larger 9,700 square-foot space at 4900 Pearl East Circle, Suite 110, in June 2011.
Kathryn Miles, president of Eetrex, said, “Eetrex is committed to supporting the community and establishing our business as an environmentally conscious company. Not only is our technology helping to green the transportation industry and support alternative energy, but we also encourage employees to ride their bicycles to work along with our zero waste practices. We are very pleased to receive this award in recognition of our efforts.”
The flexible rebate program uses social, community, and environmental sustainability guidelines. Companies choose the guidelines that best fit their circumstances, but must meet minimum requirements in order to receive the rebate. Eetrex has exceeded the minimum requirements of the community sustainability guidelines. Of note, Eetrex is implementing a zero waste policy through Green Girl Recycling and is a member of the 10 for Change challenge, which included an energy audit of its facility. The company also will request an EnergySmart training through the city’s Local Environmental Action Division.
Eetrex’s flexible rebate application is one of six submitted to the city in late 2011. Four 2011 applications are pending. The city’s approved 2012 budget includes $350,000 in funding for 2012 flexible tax and fee rebates for primary employers.
For more information about the city’s economic vitality program, go to www.bouldercolorado.gov, click on “Business,” or call Liz Hanson at 303-441-3287.