Posts tagged mountain
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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CU scientists study high-Asian snowpack for GW clues
Dec 7th
USAID, CU-BOULDER PARTNER TO STUDY
WATER RESOURCES IN ASIA MOUNTAINS
WATER RESOURCES IN ASIA MOUNTAINS
A University of Colorado Boulder team is partnering with the United States Agency for International Development to assess snow and glacier contributions to water resources originating in the high mountains of Asia that straddle 10 countries.
Richard Armstrong and Mark Williams, the two faculty members leading the four-year study, said the aim is to provide a comprehensive and systematic assessment of freshwater resources in the so-called “High Asia” region, which encompasses five mountain ranges and watersheds totaling roughly 1 million square miles. The area under study is roughly equal to one-third of the contiguous United States.
This assessment will be crucial in helping to forecast the future availability and vulnerability of water resources in the region, beginning with accurate assessments of the distinct, separate contributions to river discharge from melting glacier ice and seasonal snow. Such data ultimately will provide a better understanding of the timing and volume of runoff in the face of climate change, said the CU-Boulder researchers.
The High Asia mountains funnel water into such major river basins as the Ganges, Brahmaputra, Indus, Amu Darya and Syr Darya. The High Asian mountain ranges under study include the Himalaya, Karkoram, Hindu Kush, Pamir and Tien Shan. The mountain ranges straddle Bhutan, Nepal, China, India, Pakistan, Afghanistan, Kazakhstan, Uzbekistan, Kyrgyzstan and Tajikistan.
Through the partnership, scientists and students within the 10 countries will carry out collaborative research with CU-Boulder scientists. The project also will support satellite data processing by CU-Boulder staff and trainings for local institutions and observers within the study area to collect water and precipitation samples for the project.
While about one-third of the world’s population depends to some degree on fresh water within the High Asia hydrological system, not enough data exists on river and stream flows and the contribution of seasonal snow and glacier melt to paint an accurate picture of the water resources there, said Armstrong, a senior research scientist at CU-Boulder’s National Snow and Ice Data Center, or NSIDC. ”
The team requires an accurate quantitative portrait of each major river basin and sub-basin in High Asia. The Indus River, for example, which is fed by waterways from the Himalaya, Karakorum and Hindu Kush mountain ranges, comes together at the city of Besham, Pakistan, “where it immediately turns into the largest irrigation system in the world,” said Williams. “The sources of water in High Asia feeding the major foothill regions where most of the people live are really the crux of this study.”
Armstrong said there is a lot of misinformation in the public arena regarding glaciers, including reports that glaciers in the Himalaya are receding faster than anywhere else in the world and, if this rapid melting continues, rivers are on track to first flood and then dry up. “Those reports simply are not true,” Armstrong said.
USAID is an independent United States government agency that provides economic, development and humanitarian assistance around the world in support of the foreign policy goals of the United States.
“USAID wants to know how the High Asia water resources affect local populations,” said Armstrong, also a fellow at the CU-headquartered Cooperative Institute for Research in Environmental Sciences. “They are looking at this challenge from a sustainability perspective, including what is going to happen to rivers like the Indus and the Brahmaputra in the next 20 years.”
The researchers will use remote-sensing satellite data from NASA, the European Space Agency and the Japanese Space Agency to develop time-series maps of seasonal snowfall amounts and recent changes in glacier extent, said Williams, a fellow at CU-Boulder’s Institute of Arctic and Alpine Research and a CU-Boulder geography professor. They also will use local meteorological and river discharge data from throughout the High Asia study area.
“What’s really driving this study are questions about water security,” said Williams. “There is a lot of international interest in accurate water resource data from the High Asia region and what the water security consequences are, since water conflicts between countries can escalate rapidly. This study should provide answers as to what is real and what is false.”
“Once we have a picture of recent and current conditions, we can go forward and run computer ‘melt models’ based on the temperatures at various elevations, giving us trends in snowmelt and glacier melt by region and time,” said Armstrong. “That’s when we start to come up with water volumes for individual rivers and streams from both melting snow and ice.”
The modeling results will be verified using geochemical and water isotope “tracer” techniques developed at CU that allow researchers to follow water as it courses through mountain landscapes. Previous studies by Williams and his research group showed high mountain groundwater in Colorado dominated by snowmelt can be locked underground for decades before emerging into downstream waterways. “These isotopic and geochemical measurements provide unique fingerprints, allowing a CSI-like approach to tracing water sources,” said Williams.
Critical to the project is the university’s expertise in remote sensing research through NSIDC — including assessing changes in Earth’s snow and ice cover — and INSTAAR’s research on the physical, chemical and biological processes in “critical zones,” which are the areas between treetops and groundwater. INSTAAR administers both the Long-Term Ecological Research site at Niwot Ridge west of Boulder and the Critical Zone Observatory project in the Boulder Creek watershed for the National Science Foundation.
One of the biggest project challenges will be to obtain data from some of the most remote regions on Earth, said Williams. The water, rain and snow samples collected by collaborators within the study area will be sent back to CU-Boulder for analysis.
The research will bring together scientists and government officials in the countries of High Asia to coordinate and compare results on what part of river flows come from glaciers and seasonal snow. This sharing of information is important because the rivers of Asia can cross several country borders. USAID support will contribute to the research and coordination and CU-Boulder will make its archived and new data on snow and ice easily available to all the countries and their citizens.
The CU team will hire Asian project managers and collaborate with research scientists affiliated with various Asian institutes. “We already have some good scientific contacts in the region, people we know who are reliable and who can deliver,” said Armstrong.
A number of CU undergraduate and graduate students will be involved in the study and support will be available to Asian students by way of the funding provided to Asian project partners.
“One of the main project goals is to transfer scientific understanding to people in the region who can continue these measurements and analysis once the USAID project is finished,” said Armstrong. “The idea is to provide the local population with the information they need to make decisions that will increase sustainability as land use and climate change.
Boulder Army Store – Holiday Gifts
Dec 1st
Jann Scott goes to the Boulder Army Store to look at the great selection of holiday gifts and winter gear for your friends and family have fun and stay warm in the cold and snow.
