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CU-NOAA study shows summer climate change, mostly warming
Nov 15th
Analysis of 90 years of observational data has revealed that summer climates in regions across the globe are changing — mostly, but not always, warming –according to a new study led by a scientist from the Cooperative Institute for Research in Environmental Sciences headquartered at the University of Colorado Boulder.
“It is the first time that we show on a local scale that there are significant changes in summer temperatures,” said lead author CIRES scientist Irina Mahlstein. “This result shows us that we are experiencing a new summer climate regime in some regions.”
The technique, which reveals location-by-location temperature changes rather than global averages, could yield valuable insights into changes in ecosystems on a regional scale. Because the methodology relies on detecting temperatures outside the expected norm, it is more relevant to understand changes to the animal and plant life of a particular region, which scientists would expect to show sensitivity to changes that lie outside of normal variability.
“If the summers are actually significantly different from the way that they used to be, it could affect ecosystems,” said Mahlstein, who works in the Chemical Sciences Division of the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory.
To identify potential temperature changes, the team used climate observations recorded from 1920 to 2010 from around the globe. The scientists termed the 30-year interval from 1920 to 1949 the “base period,” and then compared the base period to other 30-year test intervals starting every 10 years since 1930.
The comparison used statistics to assess whether the test interval differed from the base period beyond what would be expected due to yearly temperature variability for that geographical area.
Their analysis found that some changes began to appear as early as the 1960s, and the observed changes were more prevalent in tropical areas. In these regions, temperatures varied little throughout the years, so the scientists could more easily detect any changes that did occur, Mahlstein said.
The scientists found significant summer temperature changes in 40 percent of tropical areas and 20 percent of higher-latitude areas. In the majority of cases, the researchers observed warming summer temperatures, but in some cases they observed cooling summer temperatures.
“This study has applied a new approach to the question, ‘Has the temperature changed in local areas?’ ” Mahlstein said. The study is in press in the journal Geophysical Research Letters, a publication of the American Geophysical Union.
The study’s findings are consistent with other approaches used to answer the same question, such as modeling and analysis of trends, Mahlstein said. But this technique uses only observed data to come to the same result. “Looking at the graphs of our results, you can visibly see how things are changing,” she said.
In particular the scientists were able to look at the earlier time periods, note the temperature extremes, and observe that those values became more frequent in the later time periods. “You see how the extreme events of the past have become a normal event,” Mahlstein said.
The scientists used 90 years of data for their study, a little more than the average lifespan of a human being. So if inhabitants of those areas believe that summers have changed since they were younger, they can be confident it is not a figment of their imagination.
“We can actually say that these changes have happened in the lifetime of a person,” Mahlstein said.
Co-authors on the study were Gabriele Hegerl from the University of Edinburgh in Scotland and Susan Solomon from Massachusetts Institute of Technology.
CIRES is a joint institute of CU-Boulder and NOAA.
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2001-02 drought helped to shift Rocky Mountain pine beetle outbreak into epidemic
Nov 5th
A new University of Colorado Boulder study shows for the first time that episodes of reduced precipitation in the southern Rocky Mountains, especially during the 2001-02 drought, greatly accelerated development of the mountain pine beetle epidemic.
The study, the first ever to chart the evolution of the current pine beetle epidemic in the southern Rocky Mountains, compared patterns of beetle outbreak in the two primary host species, the ponderosa pine and lodgepole pine, said CU-Boulder doctoral student Teresa Chapman. The current mountain pine beetle outbreak in the southern Rockies — which range from southern Wyoming through Colorado and into northern New Mexico –is estimated to have impacted nearly 3,000 square miles of forests, said Chapman, lead study author.
While the 2001-02 drought in the West played a key role in pushing the pine beetle outbreak into a true regional epidemic, the outbreak continued to gain ground even after temperature and precipitation levels returned to levels nearer the long-term averages, said Chapman of CU-Boulder’s geography department. The beetles continued to decimate lodgepole pine forests by moving into wetter and higher elevations and into less susceptible tree stands — those with smaller diameter lodgepoles sharing space with other tree species.
“In recent years some researchers have thought the pine beetle outbreak in the southern Rocky Mountains might have started in one place and spread from there,” said Chapman. “What we found was that the mountain pine beetle outbreak originated in many locations. The idea that the outbreak spread from multiple places, then coalesced and continued spreading, really highlights the importance of the broad-scale drivers of the pine beetle epidemic like climate and drought.”
A paper on the subject was recently published in the journal Ecology. Co-authors on the study include CU-Boulder geography Professor Thomas Veblen and Tania Schoennagel, an adjunct faculty member in the geography department and a research scientist at CU-Boulder’s Institute of Arctic and Alpine Research. The National Science Foundation funded the study.
Mountain pine beetles are native insects that have shaped the forests of North America for thousands of years. They range from Canada to Mexico and are found at elevations from sea level to 11,000 feet. The effects of pine beetles are especially evident in recent years on Colorado’s Western Slope, including Rocky Mountain National Park, with a particularly severe epidemic occurring in Grand and Routt counties.
Chapman said the most recent mountain pine beetle outbreak began in the 1990s, primarily in scattered groups of lodgepole pine trees living at low elevations in areas of lower annual precipitation. Following the 2001-02 drought, the outbreak was “uncoupled” from the initial weather and landscape conditions, triggering a rise in beetle populations on the Western Slope and propelling the insects over the Continental Divide into the northern Front Range to infect ponderosa pine, Chapman said.
The current pine beetle epidemic in the southern Rocky Mountains was influenced in part by extensive forest fires that ravaged Colorado’s Western Slope from roughly 1850 to 1890, said Chapman. Lodgepole pine stands completely burned off by the fires were succeeded by huge swaths of seedling lodgepoles that eventually grew side by side into dense mature stands, making them easier targets for the pine beetles.
“The widespread burning associated with dry years in the 19th century set the stage for the current outbreak by creating vast areas of trees in the size classes most susceptible to beetle attack,” said Chapman.
Veblen said a 1980s outbreak of the pine beetle centered in Colorado’s Grand County ended when extremely low minimum temperatures were reached in the winters of 1983 and 1984, killing the beetle larvae. But during the current outbreak, minimum temperatures during all seasons have been persistently high since 1996, well above the levels of extreme cold shown to kill beetle larvae in laboratory experiments.
“This implies that under continued warming trends, future outbreaks will not be terminated until they exhaust their food supply — the pine tree hosts,” said Veblen.
Chapman said there has been a massive and unprecedented beetle epidemic in British Columbia, which also began in the early 1990s and has now has affected nearly 70,000 square miles. “It is hard to tell if this current beetle epidemic in the Southern Rockies is unprecedented,” she said. “While warm periods in the 16th century may have triggered a large beetle epidemic, any evidence would have been wiped out by the massive fires in the latter part of the 19th century.”
Veblen said while the rate of spread of the mountain pine beetle in lodgepole pine forests has declined in the southern Rocky Mountains during the past two years because of a depletion of host pine population, U.S. Forest Service surveys indicate the rate of beetle spread in ponderosa pine forests on the Front Range has increased sharply over the past three years. “The current study suggests that under the continued warmer climate, the spread of the beetle in ponderosa pines is likely to grow until that food source also is depleted,” Veblen said.
“Our results emphasize the importance of considering different patterns in the population dynamics of mountain pine beetles for different host species, even under similar regional-scale weather variations,” said Chapman. “Given the current outbreak of mountain pine beetles on the Front Range, their impact on ponderosa pines is certainly something that needs further study.”
A 2012 study by CU-Boulder Professor Jeffry Mitton and graduate student Scott Ferrenberg showed some Colorado pine beetles, which had been known to produce only one generation of tree-killing offspring annually, are producing two generations per year due to rising temperatures and a longer annual warm season. Because of the extra annual generation of beetles, there could be up to 60 times as many beetles attacking trees in any given year, according to the study.
In addition, a 2011 study led by CU-Boulder graduate student Evan Pugh indicated the infestation of trees by mountain pine beetles in the high country across the West could potentially trigger earlier snowmelt and increase water yields from snowpack that accumulates beneath affected trees.
CU Boulder study finds racial ‘hierarchy of bias’ drives decision to shoot armed, unarmed suspects
Oct 24th
Police officers and students exhibit an apparent “hierarchy of bias” in making a split-second decision whether to shoot suspects who appear to be wielding a gun or, alternatively, a benign object like a cell phone, research conducted by the University of Colorado Boulder and San Diego State University has found.
Both the police and student subjects were most likely to shoot at blacks, then Hispanics, then whites and finally, in a case of what might be called a positive bias, Asians, researchers found.
In the first study of its kind, Joshua Correll, Bernadette Park and Charles M. Judd of CU-Boulder’s Department of Psychology and Neuroscience and Melody Sadler of San Diego State University examined how police and a group of undergraduate subjects decide whether to shoot or not to shoot “suspects” in a multi-ethnic environment.
“Most studies on the subject of stereotyping and prejudice look at two (ethnic) groups, usually in isolation. It’s always one group against another group,” said Correll, a CU graduate who joined the faculty in August after a stint at the University of Chicago.
“But as the country becomes more ethnically diverse, it’s more and more important to start thinking about how we process racial and ethnic cues in a multicultural environment,” he said.
As with previous studies into the question, data were gathered from subjects playing a “first person shooter” video game, in which figures of varying ethnicity — Caucasian, Asian, Hispanic and African-American — pop up, either “armed” with a weapon or another benign object, such as a cell phone.
Participants — 69 CU-Boulder undergraduates and 254 police officers — had to make quick decisions as to which figures posed a “threat” and shoot them. The police officers were recruited from two-day training seminars in Florida, New Mexico and Washington and represented numerous jurisdictions from 11 states.
The research demonstrates how persistent cultural stereotypes are, Correll said. Even students who displayed little bias when interviewed demonstrated otherwise when faced with a split-second decision.
“I may not believe it personally, but I am exposed to stereotypes constantly through media or social networks … (such as) the idea that young black men are dangerous,” he said. “Those associations can have an influence on my behavior even if I don’t believe them.”
The study found that police were considerably more accurate than students at correctly identifying a genuinely threatening suspect, as opposed to those brandishing a cell phone or wallet, perhaps a reflection of training. But officers were still influenced by the target’s race — an influence that may derive from the officers’ “contacts, attitudes and stereotypes,” Correll said.
For example, police who endorsed more violent stereotypes about Hispanics and those who overestimated the prevalence of violent crime in their districts demonstrated more bias to shoot Hispanic targets. That raises the question of whether police are responding to real-world threats — and whether that means some ethnic groups really are more likely to be armed and dangerous than others.
“That is a very sensitive question, whether or not (police officers’) reactions are based on some kind of truth. Is this police officers responding to reality on the ground? The short answer is, we don’t know,” Correll said. “But this research almost demands that we ask that question.”
The researchers’ recent findings were published in the Journal of Social Issues. The work was funded by a grant from the Russell Sage Foundation.
In 2007, Correll (then at the University of Chicago), Sadler (then at CU-Boulder), Park and Judd collaborated with the Denver Police Department on a widely cited study that found police officers were less influenced than the general public by racial bias and less likely than the general population to make a decision to shoot at African-American suspects wielding a benign object.
-C
