Glacier beds can get slipperier at higher sliding speeds

As a glacier's sliding speed increases, the bed beneath the glacier can grow slipperier, according to laboratory experiments conducted by Iowa State University glaciologists.

They say including this effect in efforts to calculate future increases in glacier speeds could improve predictions of ice volume lost to the oceans and the rate of sea-level rise.

The glaciologists -- Lucas Zoet, a postdoctoral research associate, and Neal Iverson, a professor of geological and atmospheric sciences -- describe the results of their experiments in the Journal of Glaciology. The paper uses data collected from a newly constructed laboratory tool, the Iowa State University Sliding Simulator, to investigate glacier sliding. The device was used to explore the relationship between drag and sliding speed for comparison with the predictions of theoretical models.

"We really have a unique opportunity to study the base of glaciers with these experiments," said Zoet, the lead author of the paper. "The other tactic you might take is studying these relationships with field observations, but with field data so many different processes are mixed together that it becomes hard to untangle the relevant data from the noise."

Data collected by the researchers show that resistance to glacier sliding -- the drag that the bed exerts on the ice -- can decrease in response to increasing sliding speed. This decrease in drag with increasing speed, although predicted by some theoreticians a long as 45 years ago, is the opposite of what is usually assumed in mathematical models of the flow of ice sheets.

These are the first empirical results demonstrating that as ice slides at an increasing speed -- perhaps in response to changing weather or climate -- the bed can become slipperier, which could promote still faster glacier flow.

The response of glaciers to changing climate is one of the largest potential contributors to sea-level rise. Predicting glacier response to climate change depends on properly characterizing the way a glacier slides over its bed. There has been a half-century debate among theoreticians as to how to do that.

The simulator features a ring of ice about 8 inches thick and about 3 feet across that is rotated over a model glacier bed. Below the ice is a hydraulic press that can simulate the weight of a glacier several hundred yards thick. Above are motors that can rotate the ice ring over the bed at either a constant speed or a constant stress. A circulating, temperature-regulated fluid keeps the ice at its melting temperature -- a necessary condition for significant sliding.

"About six years were required to design, construct, and work the bugs out of the new apparatus," Iverson said, "but it is performing well now and allowing hypothesis tests that were formerly not possible."

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Temperature anomalies are warming faster than Earth's average, study finds

It's widely known that Earth's average temperature has been rising. But research by an Indiana University geographer and colleagues finds that spatial patterns of extreme temperature anomalies -- readings well above or below the mean -- are warming even faster than the overall average.

And trends in extreme heat and cold are important, said Scott M. Robeson, professor of geography in the College of Arts and Sciences at IU Bloomington. They have an outsized impact on water supplies, agricultural productivity and other factors related to human health and well-being.

"Average temperatures don't tell us everything we need to know about climate change," he said. "Arguably, these cold extremes and warm extremes are the most important factors for human society."

Robeson is the lead author of the article "Trends in hemispheric warm and cold anomalies," which will be published in the journal Geophysical Research Letters and is available online. Co-authors are Cort J. Willmott of the University of Delaware and Phil D. Jones of the University of East Anglia.

The researchers analyzed temperature records for the years 1881 to 2013 from HadCRUT4, a widely used data set for land and sea locations compiled by the University of East Anglia and the U.K. Met Office. Using monthly average temperatures at points across the globe, they sorted them into "spatial percentiles," which represent how unusual they are by their geographic size.

Their findings include:

Temperatures at the cold and warm "tails" of the spatial distribution -- the 5th and 95th percentiles -- increased more than the overall average Earth temperature.Over the 130-year record, cold anomalies increased more than warm anomalies, resulting in an overall narrowing of the range of Earth's temperatures.In the past 30 years, however, that pattern reversed, with warm anomalies increasing at a faster rate than cold anomalies. "Earth's temperature was becoming more homogenous with time," Robeson said, "but now it's not."

The study records separate results for the Northern and Southern Hemispheres. Temperatures are considerably more volatile in the Northern Hemisphere, an expected result because there's considerably less land mass in the South to add complexity to weather systems.

The study also examined anomalies during the "pause" in global warming that scientists have observed since 1998. While a 16-year-period is too short a time to draw conclusions about trends, the researchers found that warming continued at most locations on the planet and during much of the year, but that warming was offset by strong cooling during winter months in the Northern Hemisphere.

"There really hasn't been a pause in global warming," Robeson said. "There's been a pause in Northern Hemisphere winter warming."

Co-author Jones of the University of East Anglia said the study provides scientists with better knowledge about what's taking place with Earth's climate. "Improved understanding of the spatial patterns of change over the three periods studied are vital for understanding the causes of recent events," he said.

It may seem counterintuitive that global warming would be accompanied by colder winter weather at some locales. But Robeson said the observation aligns with theories about climate change, which hold that amplified warming in the Arctic region produces changes in the jet stream, which can result in extended periods of cold weather at some locations in the mid-northern latitudes.

And while the rate of planetary warming has slowed in the past 16 years, it hasn't stopped. The World Meteorological Organization announced this month that 2014 is on track to be one of the warmest, if not the warmest, years on record as measured by global average temperatures.

In the U.S., the East has been unusually cold and snowy in recent years, but much of the West has been unusually warm and has experienced drought. And what happens here doesn't necessarily reflect conditions on the rest of the planet. Robeson points out that the United States, including Alaska, makes up only 2 percent of Earth's surface.

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When it comes to variations in crop yield, climate has a big say

What impact will future climate change have on food supply? That depends in part on the extent to which variations in crop yield are attributable to variations in climate. A new report from researchers at the University of Minnesota Institute on the Environment has found that climate variability historically accounts for one-third of yield variability for maize, rice, wheat and soybeans worldwide -- the equivalent of 36 million metric tons of food each year. This provides valuable information planners and policy makers can use to target efforts to stabilize farmer income and food supply and so boost food security in a warming world.

The work was published in the journal Nature Communications by Deepak Ray, James Gerber, Graham MacDonald and Paul West of IonE's Global Landscapes Initiative.The researchers looked at newly available production statistics for maize, rice, wheat and soybean from 13,500 political units around the world between 1979 and 2008, along with precipitation and temperature data. The team used these data to calculate year-to-year fluctuations and estimate how much of the yield variability could be attributed to climate variability.About 32 to 39 percent of year-to-year variability for the four crops could be explained by climate variability. This is substantial -- the equivalent of 22 million metric tons of maize, 3 million metric tons of rice, 9 million metric tons of wheat, and 2 million metric tons of soybeans per year.The links between climate and yield variability differed among regions. Climate variability explained much of yield variability in some of the most productive regions, but far less in low-yielding regions. "This means that really productive areas contribute to food security by having a bumper crop when the weather is favorable but can be hit really hard when the weather is bad and contribute disproportionately to global food insecurity," says Ray. "At the other end of the spectrum, low-yielding regions seem to be more resilient to bad-weather years but don't see big gains when the weather is ideal." Some regions, such as in parts of Asia and Africa, showed little correlation between climate variability and yield variability.More than 60 percent of the yield variability can be explained by climate variability in regions that are important producers of major crops, including the Midwestern U.S., the North China Plains, western Europe and Japan.Depicted as global maps, the results show where and how much climate variability explains yield variability.

The research team is now looking at historical records to see whether the variability attributable to climate has changed over time -- and if so, what aspects of climate are most pertinent.

"Yield variability can be a big problem from both economic and food supply standpoints," Ray said. "The results of this study and our follow-up work can be used to improve food system stability around the world by identifying hot spots of food insecurity today as well as those likely to be exacerbated by climate change in the future."

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The legend of the Kamikaze typhoons

In the late 13th century, Kublai Khan, ruler of the Mongol Empire, launched one of the world's largest armada of its time in an attempt to conquer Japan. Early narratives describe the decimation and dispersal of these fleets by the "Kamikaze" of CE 1274 and CE 1281 -- a pair of intense typhoons divinely sent to protect Japan from invasion.

These historical accounts are prone to exaggeration, and significant questions remain regarding the occurrence and true intensity of these legendary typhoons. For independent insight, we provide a new 2,000 year sedimentary reconstruction of typhoon overwash from a coastal lake near the location of the Mongol invasions. Two prominent storm deposits date to the timing of the Kamikaze typhoons and support them being of significant intensity.

Our new storm reconstruction also indicates that events of this nature were more frequent in the region during the timing of the Mongol invasions. Results support the paired Kamikaze typhoons in having played an important role in preventing the early conquest of Japan by Mongol fleets. In doing so, the events may provide one of the earliest historical cases for the shaping of a major geopolitical boundary by an increased probability of extreme weather due to changing atmospheric and oceanic conditions.

Journal Reference:

J. D. Woodruff, K. Kanamaru, S. Kundu, T. L. Cook. Depositional evidence for the Kamikaze typhoons and links to changes in typhoon climatology. Geology, 2014; DOI: 10.1130/G36209.1

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Global warming's influence on extreme weather

Understanding the cause-and-effect relationship between global warming and record-breaking weather requires asking precisely the right questions.

Extreme climate and weather events such as record high temperatures, intense downpours and severe storm surges are becoming more common in many parts of the world. But because high-quality weather records go back only about 100 years, most scientists have been reluctant to say if global warming affected particular extreme events.

On Wednesday, Dec. 17, at the American Geophysical Union's Fall Meeting in San Francisco, Noah Diffenbaugh, an associate professor of environmental Earth system science at the Stanford School of Earth Sciences, will discuss approaches to this challenge in a talk titled "Quantifying the Influence of Observed Global Warming on the Probability of Unprecedented Extreme Climate Events." He will focus on weather events that -- at the time they occur -- are more extreme than any other event in the historical record.

Diffenbaugh emphasizes that asking precisely the right question is critical for finding the correct answer.

"The media are often focused on whether global warming caused a particular event," said Diffenbaugh, who is a senior fellow at the Stanford Woods Institute for the Environment. "The more useful question for real-world decisions is: 'Is the probability of a particular event statistically different now compared with a climate without human influence?'"

Diffenbaugh said the research requires three elements: a long record of climate observations; a large collection of climate model experiments that accurately simulate the observed variations in climate; and advanced statistical techniques to analyze both the observations and the climate models.

One research challenge involves having just a few decades or a century of high-quality weather data with which to make sense of events that might occur once every 1,000 or 10,000 years in a theoretical climate without human influence.

But decision makers need to appreciate the influence of global warming on extreme climate and weather events.

"If we look over the last decade in the United States, there have been more than 70 events that have each caused at least $1 billion in damage, and a number of those have been considerably more costly," said Diffenbaugh. "Understanding whether the probability of those high-impact events has changed can help us to plan for future extreme events, and to value the costs and benefits of avoiding future global warming."

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In the mood to trade? Weather may influence institutional investors' stock decisions

Weather changes may affect how institutional investors decide on stock plays, according to a new study by a team of finance researchers. Their findings suggest sunny skies put professional investors more in a mood to buy, while cloudy conditions tend to discourage stock purchases.

The researchers conclude that cloudier days increase the perception that individual stocks and the Dow Jones Industrials are overpriced, increasing the inclination for institutions to sell.

The research paper, "Weather-Induced Mood, Institutional Investors, and Stock Returns," has been published in the January 2015 issue of The Review of Financial Studies. The research was collaborated by Case Western Reserve University's Dasol Kim and three other finance professors (William Goetzmann of Yale University, Alok Kumar of University of Miami and Qin Wang of University of Michigan-Dearborn).

Institutional investors represent large organizations, such as banks, mutual funds, labor union funds and finance or insurance companies that make substantial investments in stocks. Kim said the results of the study are surprising, given that professional investors are well regarded for their financial sophistication.

"We focus on institutional investors because of the important role they have in how stock prices are formed in the markets," said Kim, assistant professor of banking and finance at Case Western Reserve's Weatherhead School of Management. "Other studies have already shown that ordinary retail investors are susceptible to psychological biases in their investment decisions. Trying to evaluate similar questions for institutional investors is challenging, because relevant data is hard to come by."

Building on previous findings from psychological studies about the effect of sunshine on mood, the researchers wanted to learn how mood affects professional investor opinions on their stock market investments.

By linking responses to a survey of investors from the Yale Investor Behavior Project of Nobel Prize-winning economist Robert Shiller and institutional stock trade data with historical weather data from the National Oceanic and Atmospheric Administration, the researchers concluded aggregated data shows that seasonably sunnier weather leads to optimistic responses and a willingness to buy.

The research accounts for differences in weather across regions of the country and seasons. They show that these documented mood effects also influence stock prices, and that the observed impact does not persist for long periods of time.

A summary of the research was also recently featured at The Harvard Law School Forum on Corporate Governance and Financial Regulation.

Journal Reference:

W. N. Goetzmann, D. Kim, A. Kumar, Q. Wang. Weather-Induced Mood, Institutional Investors, and Stock Returns. Review of Financial Studies, 2014; 28 (1): 73 DOI: 10.1093/rfs/hhu063

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