Posts tagged South America
Ice-free Arctic winters could explain amplified warming during Pliocene
Jul 29th
Year-round ice-free conditions across the surface of the Arctic Ocean could explain why the Earth was substantially warmer during the Pliocene Epoch than it is today, despite similar concentrations of carbon dioxide in the atmosphere, according to new research carried out at the University of Colorado Boulder.
The last time researchers believe the carbon dioxide concentration in the atmosphere reached 400 ppm—between 3 and 5 million years ago during the Pliocene—the Earth was about 3.5 to 9 degrees Fahrenheit warmer (2 to 5 degrees Celsius) than it is today. During that time period, trees overtook the tundra, sprouting right to the edges of the Arctic Ocean, and the seas swelled, pushing ocean levels 65 to 80 feet higher.
Scientists’ understanding of the climate during the Pliocene has largely been pieced together from fossil records preserved in sediments deposited beneath lakes and on the ocean floor.
“When we put 400 ppm carbon dioxide into a model, we don’t get as warm a planet as we see when we look at paleorecords from the Pliocene,” said Jim White, director of CU-Boulder’s Institute of Arctic and Alpine Research and co-author of the new study published online in the journal Palaeogeography, Paleoclimatology, Palaeoecology. “That tells us that there may be something missing in the climate models.”
Scientists have proposed several hypotheses in the past to explain the warmer Pliocene climate. One idea, for example, was that the formation of the Isthmus of Panama, the narrow strip of land linking North and South America, could have altered ocean circulations during the Pliocene, forcing warmer waters toward the Arctic. But many of those hypotheses, including the Panama possibility, have not proved viable.
For the new study, led by Ashley Ballantyne, a former CU-Boulder doctoral student who is now an assistant professor of bioclimatology at the University of Montana, the research team decided to see what would happen if they forced the model to assume that the Arctic was free of ice in the winter as well as the summer during the Pliocene. Without these additional parameters, climate models set to emulate atmospheric conditions during the Pliocene show ice-free summers followed by a layer of ice reforming during the sunless winters.
“We tried a simple experiment in which we said, ‘We don’t know why sea ice might be gone all year round, but let’s just make it go away,’ ” said White, who also is a professor of geological sciences. “And what we found was that we got the right kind of temperature change and we got a dampened seasonal cycle, both of which are things we think we see in the Pliocene.”
In the model simulation, year-round ice-free conditions caused warmer conditions in the Arctic because the open water surface allowed for evaporation. Evaporation requires energy, and the water vapor then stored that energy as heat in the atmosphere. The water vapor also created clouds, which trapped heat near the planet’s surface.
“Basically, when you take away the sea ice, the Arctic Ocean responds by creating a blanket of water vapor and clouds that keeps the Arctic warmer,” White said.
White and his colleagues are now trying to understand what types of conditions could bridge the standard model simulations with the simulations in which ice-free conditions in the Arctic are imposed. If they’re successful, computer models would be able to model the transition between a time when ice reformed in the winter to a time when the ocean remained devoid of ice throughout the year.
Such a model also would offer insight into what could happen in our future. Currently, about 70 percent of sea ice disappears during the summertime before reforming in the winter.
“We’re trying to understand what happened in the past but with a very keen eye to the future and the present,” White said. “The piece that we’re looking at in the future is what is going to happen as the Arctic Ocean warms up and becomes more ice-free in the summertime.
“Will we continue to return to an ice-covered Arctic in the wintertime? Or will we start to see some of the feedbacks that now aren’t very well represented in our climate models? If we do, that’s a big game changer.”
CU-Boulder geological sciences Professor Gifford Miller also is a co-author of the study. Researchers from Northwestern University and the National Center for Atmospheric Research also were involved in the study, which was supported by a grant from the National Science Foundation.
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CU project: Degraded military lands to get ecological boost
Nov 15th
Headed up by CU-Boulder Assistant Professor Nichole Barger, the research team is focused on developing methods to restore biological soil crusts — microbial communities primarily concentrated on soil surfaces critical to decreasing erosion and increasing water retention and soil fertility. Such biological soil crusts, known as “biocrusts,” can cover up to 70 percent of the ground in some arid ecosystems and are dominated by cyanobacteria, lichens, mosses, fungi and bacteria, she said.
The project is aimed at restoring fragile habitats in desert areas that have been affected by the movement of U.S. military vehicles, including tanks, as well as high foot traffic, said Barger, a faculty member in CU-Boulder’s ecology and environmental biology department. The team has two U.S. Department of Defense study sites — Fort Bliss, which straddles southern Texas and New Mexico and is located in a hot desert environment, and the Dugway Proving Ground in northwest Utah, seated in a cool desert environment.
“Biocrusts often are associated with increased soil nutrients and water retention, but their most important task is to stabilize soil surfaces against wind and water erosion,” Barger said. “While most biocrusts are relatively resilient to wind and water erosion, they are highly susceptible to compressional forces like those generated by foot and vehicle traffic associated with ground-based military activities.”
At military installations like Fort Bliss, the Dugway Proving Ground and in the California/Arizona Maneuver Area in the Mojave Desert used by Patton’s troops, scars of past military activity still are evident, said Barger. “You can go to these places and see that the biocrusts in the old tank tracks, for example, are completely different than nearby biocrusts undisturbed by military activity.”
The project is being funded by a five-year, $2.3 million grant from the Strategic Environmental Research and Development Program, the U.S. Department of Defense environmental science and technology program that partners with the U.S. Department of Energy and the Environmental Protection Agency. The research team also includes Jayne Belnap, Michael Duniway and Sasha Reed from the U.S. Geological Survey’s Biological Resources Division in Moab, Utah and Ferran Garcia-Pichel of Arizona State University in Tempe.
The first step of the program will be to grow biocrusts in laboratories at ASU, said Barger. “Our approach will be to expose laboratory biocrusts over time to a physiological ‘boot camp’ that includes increasing stressors like heat, light and dryness,” she said. “By doing that, we believe the biocrusts we eventually transplant into the study areas will have a higher probability of survival.”
The lab-grown biocrust products will be dried, bagged and transported to field test sites at each respective military installation and sprinkled on soil surfaces, said Barger.
Once in the field, the stress-adapted biocrusts developed in the lab nurseries for both hot desert and cool desert environments will be combined with other soil stabilization strategies, she said. The team, for example, will also experiment with adding polyacrylamide — a soil-stabilizing compound shown to increase soil porosity and reduce erosion, compaction, dustiness and water run-off — to the mix.
The researchers will evaluate the effectiveness of such soil “inoculations” and determine the optimum dosage for the test sites. Following the assisted recovery of the local biocrusts at Fort Bliss and the Dugway Proving Ground, the team will begin a series of seeding trials to develop strategies for native plant re-establishment, Barger said.
The last step of the project will involve a series of rainfall simulations and wind tunnel experiments combined with broad-scale soil erosion modeling to evaluate the influence of biocrust and native plant restoration in terms of precipitation and soil erosion.
While DOD military installations cover nearly 30 million acres — 70 percent of which are located in arid regions of the West — Barger said the research also could aid in the effective management of other federal lands. “We think our work on biocrusts also will be of interest to land managers at agencies like the Bureau of Land Management and the U.S. Forest Service,” Barger said.
The adaptation of biocrusts to extreme environments likely will come into play even more as climate change continues to heat and dry the West, she said. “We expect the drought in the Southwest to intensify as a result of climate change, and this project should tell us more about how adaptive these biocrusts are under shifting environmental conditions.”
The research project also has health implications, said Barger, since the disturbance of biocrusts can trigger the release of significant amounts of atmospheric dust, a dominant pollutant in some desert metropolitan areas. “There is a broad societal interest in stabilizing dryland soils in order to protect not only the functioning of local ecosystems but also human populations that reside in surrounding communities.”
“In terms of tackling an important environmental issue, this is by far the most exciting research project that I have been involved in,” said Barger, who has worked in Hawaii, Central America, South America, China and South Africa.
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Evidence of global climate in Southern Hemisphere
Aug 22nd
SOUTHERN SOUTH AMERICAN WILDFIRES
EXPECTED TO INCREASE, SAYS CU STUDY
A new University of Colorado Boulder study indicates a major climate oscillation in the Southern Hemisphere that is expected to intensify in the coming decades will likely cause increased wildfire activity in the southern half of South America.
The research team used tree rings dating to 1506 to track past wildfire activity in the forests of Patagonia tied to the Southern Annular Mode, or SAM, a climate oscillation that creates low atmospheric pressure in the Antarctic that is tied to warmer and drier conditions in southern South America. The tree rings showed that when SAM was in its positive phase, there were widespread fires in both dry woodlands and rainforests in Patagonia, a region that straddles Argentina and Chile, said CU-Boulder Research Associate Andres Holz, lead study author.
“Our study shows for about the past 250 years, the Southern Annular Mode has been the main driver in creating droughts and fires in two very different ecosystems in southern South America,” said Holz. “Climate models suggest an increase in SAM beginning in the 1960s due to greenhouse gas increases and Antarctic ozone depletion probably will cause this region to be drought-prone and fire-prone for at least the next 100 years.”
A paper on the subject by Holz and CU-Boulder geography Professor Thomas Veblen was published in Geophysical Research Letters.
Holz and Veblen compared past wildfire records for two ecologically distinct regions in Patagonia — the relatively dry region of southern Patagonia in Argentina and the temperate rainforest of Patagonia in northern Chile. While the tree ring historical record showed increased fires in both regions correlated with a positive SAM, the trend has been less pronounced in northern Patagonia in the past 50 years, likely because of fire-suppression efforts there, Holz said.
But the decades of fire suppression have caused the northern Patagonian woodlands to become denser and more prone towildfire during hot and dry years, Holz said.
“Even in areas of northern Patagonia where fire suppression previously had been effective, record surface areas of woodlands and forests have burned in recent years of extreme drought,” said Veblen. “And since this is in an area of rapid residential growth into wildland-urban interface areas, this climate-driven trend towards increasing fire risk is becoming a major problem for land managers and homeowners.”
The two CU-Boulder researchers studied reconstructions of tree rings going back more than 500 years from 432 trees at 42 sample sites in northern Argentina and southern Chile — the largest available data set of annual, readable tree ring records in the Southern Hemisphere. The tree rings, which indicate climate cycles and reveal the scars of old fires, showed that wildfires generally increased in both regions when SAM was in its strong, positive phase.
Although the Antarctic ozone hole stopped growing in about 2000 as a result of a ban on ozone-depleting gases and now appears to be slowly repairing itself, a 2011 paper by researchers at the National Center for Atmospheric Research in Boulder indicates ozone recovery and greenhouse gas influences essentially will cancel each other out, preventing SAM from returning to its pre-1960s levels.
“Before the Industrial Revolution, SAM intensified naturally at times to create drought situations in Patagonia,” Holz said. “But in the last 80 years or so, the natural variation has been overwhelmed by a bias toward a positive SAM phase because of ozone-depleting chemicals and greenhouse gases we have put in the atmosphere.”
The research effort was supported by the National Geographic Society, the National Science Foundation, the CU Beverly Sears Small Grants Program and the Council on Research and CreativeResearch of the CU Graduate School.
“As warming and drying trends continue, it is likely that wildfire activity will increase even in woodland areas where fire suppression has previously been effective,” Holz and Veblen wrote in Geophysical Research Letters.