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- 19-10-2010 eco nws - global warming - impact - weather - drought - Drought May Threaten Much of Globe Within Decades, Analysis Predicts - ScienceDaily (Oct. 19, 2010) � The United States and many other heavily populated countries face a growing threat of severe and prolonged drought in coming decades, according to a new study by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai. The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years, possibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times. Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper finds most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia, may be at threat of extreme drought this century. In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become more moist. Dai cautioned that the findings are based on the best current projections of greenhouse gas emissions. What actually happens in coming decades will depend on many factors, including actual future emissions of greenhouse gases as well as natural climate cycles such as El Ni�o. The new findings appear as part of a longer review article in Wiley Interdisciplinary Reviews: Climate Change. The study was supported by the National Science Foundation, NCAR's sponsor. "We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community," Dai says. "If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous." While regional climate projections are less certain than those for the globe as a whole, Dai's study indicates that most of the western two-thirds of the United States will be significantly drier by the 2030s. Large parts of the nation may face an increasing risk of extreme drought during the century. Other countries and continents that could face significant drying include: * Much of Latin America, including large sections of Mexico and Brazil * Regions bordering the Mediterranean Sea, which could become especially dry * Large parts of Southwest Asia * Most of Africa and Australia, with particularly dry conditions in regions of Africa * Southeast Asia, including parts of China and neighboring countries The study also finds that drought risk can be expected to decrease this century across much of Northern Europe, Russia, Canada, and Alaska, as well as some areas in the Southern Hemisphere. However, the globe's land areas should be drier overall. "The increased wetness over the northern, sparsely populated high latitudes can't match the drying over the more densely populated temperate and tropical areas," Dai says. A climate change expert not associated with the study, Richard Seager of Columbia University's Lamont Doherty Earth Observatory, adds: "As Dai emphasizes here, vast swaths of the subtropics and the midlatitude continents face a future with drier soils and less surface water as a result of reducing rainfall and increasing evaporation driven by a warming atmosphere. The term 'global warming' does not do justice to the climatic changes the world will experience in coming decades. Some of the worst disruptions we face will involve water, not just temperature." - A portrait of worsening drought - Previous climate studies have indicated that global warming will probably alter precipitation patterns as the subtropics expand. The 2007 assessment by the Intergovernmental Panel on Climate Change (IPCC) concluded that subtropical areas will likely have precipitation declines, with high-latitude areas getting more precipitation. In addition, previous studies by Dai have indicated that climate change may already be having a drying effect on parts of the world. In a much-cited 2004 study, he and colleagues found that the percentage of Earth's land area stricken by serious drought more than doubled from the 1970s to the early 2000s. Last year, he headed up a research team that found that some of the world's major rivers are losing water. In his new study, Dai turned from rain and snow amounts to drought itself, and posed a basic question: how will climate change affect future droughts? If rainfall runs short by a given amount, it may or may not produce drought conditions, depending on how warm it is, how quickly the moisture evaporates, and other factors. Droughts are complex events that can be associated with significantly reduced precipitation, dry soils that fail to sustain crops, and reduced levels in reservoirs and other bodies of water that can imperil drinking supplies. A common measure called the Palmer Drought Severity Index classifies the strength of a drought by tracking precipitation and evaporation over time and comparing them to the usual variability one would expect at a given location. Dai turned to results from the 22 computer models used by the IPCC in its 2007 report to gather projections about temperature, precipitation, humidity, wind speed, and Earth's radiative balance, based on current projections of greenhouse gas emissions. He then fed the information into the Palmer model to calculate the PDSI index. A reading of +0.5 to -0.5 on the index indicates normal conditions, while a reading at or below -4 indicates extreme drought. The most index ranges from +10 to -10 for current climate conditions, although readings below -6 are exceedingly rare, even during short periods of time in small areas. By the 2030s, the results indicated that some regions in the United States and overseas could experience particularly severe conditions, with average decadal readings potentially dropping to -4 to -6 in much of the central and western United States as well as several regions overseas, and -8 or lower in parts of the Mediterranean. By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented. Dai cautions that global climate models remain inconsistent in capturing precipitation changes and other atmospheric factors, especially at the regional scale. However, the 2007 IPCC models were in stronger agreement on high- and low-latitude precipitation than those used in previous reports, says Dai. There are also uncertainties in how well the Palmer index captures the range of conditions that future climate may produce. The index could be overestimating drought intensity in the more extreme cases, says Dai. On the other hand, the index may be underestimating the loss of soil moisture should rain and snow fall in shorter, heavier bursts and run off more quickly. Such precipitation trends have already been diagnosed in the United States and several other areas over recent years, says Dai. "The fact that the current drought index may not work for the 21st century climate is itself a troubling sign," Dai says.
- 14-12-2010 eco nws - global warming - impact - weather - drought - usa - Hot With Decades of Drought: Expectations for Southwestern United States - ScienceDaily (Dec. 14, 2010) � An unprecedented combination of heat plus decades of drought could be in store for the Southwest sometime this century, suggests new research from a University of Arizona-led team. A 60-year drought like that of the 12th Century could be in our future. To come to this conclusion, the team reviewed previous studies that document the region's past temperatures and droughts. "Major 20th century droughts pale in comparison to droughts documented in paleoclimatic records over the past two millennia," the researchers wrote. During the Medieval period, elevated temperatures coincided with lengthy and widespread droughts. By figuring out when and for how long drought and warm temperatures coincided in the past, the team identified plausible worst-case scenarios for the future. Such scenarios can help water and other resource managers plan for the future, the team wrote. "We're not saying future droughts will be worse than what we see in the paleo record, but we are saying they could be as bad," said lead author Connie A. Woodhouse, a UA associate professor of geography and regional development. "However, the effects of such a worst-case drought, were it to recur in the future, would be greatly intensified by even warmer temperatures." The team's paper is part of the special feature, "Climate Change and Water in Southwestern North America," scheduled for publication Dec. 13 in the Early Online edition of the Proceedings of the National Academy of Sciences. The paper by Woodhouse and her colleagues is titled, "A 1,200-year perspective of 21st century drought in the southwestern North America." Co-authors are Glen M. MacDonald of the University of California, Los Angeles; Dave W. Stahle of the University of Arkansas in Fayetteville; and Edward R. Cook of Lamont-Doherty Earth Observatory of Columbia University, Palisades, N.Y. The analysis in the current paper includes previous research by Woodhouse, co-author David M. Meko and others that documented past droughts that lasted several decades. Moreover, some of those droughts occurred during times of relatively warm temperatures. Within the last 2,000 years, there have been several periods of severe and sustained drought that affected much of western North America. Droughts that are accompanied by warm temperatures have more severe impacts on ecosystems, said Meko, an associate research professor in the UA's Laboratory of Tree-Ring Research. During the Medieval period, temperatures were about 1.8 degrees Fahrenheit (1 C) above the long-term average. Average temperatures in the Southwest have been warmer than that since 1990 and are projected to increase at least another 3.6 F (2 C) by 2100, Woodhouse said. The most severe warm-climate drought in the Southwest within the last 1,200 years was 60 years long and occurred during the mid-12th century, according to research by Meko and others. That drought covered most of the western U.S. and northern Mexico. For a 25-year period during that drought, Colorado River flow averaged 15 percent below normal, according to the tree-ring-based reconstruction of stream flow at Lees Ferry. For every 1.8 degree Fahrenheit (1 C) of warming in the future, Colorado River flow is projected to decrease between two and eight percent, Woodhouse and her co-authors wrote. The Colorado River supplies water for cities and agriculture in seven western states in the U.S. and two states in northwestern Mexico. Los Angeles, Las Vegas, Denver, Phoenix, Tucson and Albuquerque are among the many cities dependent on Colorado River water. "Even without warming, if you had one of those medieval droughts now, the impact would be devastating," she said. "Our water systems are not built to sustain us through that length of drought." Noting that the Colorado River flows recorded at Lees Ferry from 2000 to 2009 are the lowest on record, Woodhouse said the current drought could be part of a longer dry period. The instrumental record from Lees Ferry goes back to 1906. "As this drought unfolds you can't really evaluate it until you're looking back in time," she said. In recent decades, temperatures have been higher than during the previous 1,200 years, and future temperatures are predicted to be even warmer, Woodhouse said. In addition, other research predicts that changes in atmospheric circulation will reduce the amount of winter precipitation the Southwest receives in the future, she said. "The bottom line is, we could have a Medieval-style drought with even warmer temperatures," Woodhouse said.
- 29-01-2011 eco nws - global warming - impact - regions - drought - africa - More Frequent Drought Likely in Eastern Africa - ScienceDaily (Jan. 29, 2011) � The increased frequency of drought observed in eastern Africa over the last 20 years is likely to continue as long as global temperatures continue to rise, according to new research published in Climate Dynamics. This poses increased risk to the estimated 17.5 million people in the Greater Horn of Africa who currently face potential food shortages. Scientists from the U.S. Geological Survey and the University of California, Santa Barbara, determined that warming of the Indian Ocean, which causes decreased rainfall in eastern Africa, is linked to global warming. These new projections of continued drought contradict previous scenarios by the Intergovernmental Panel on Climate Change predicting increased rainfall in eastern Africa. This new research supports efforts by the USGS and the U.S. Agency for International Development to identify areas of potential drought and famine in order to target food aid and help inform agricultural development, environmental conservation, and water resources planning. �Global temperatures are predicted to continue increasing, and we anticipate that average precipitation totals in Kenya and Ethiopia will continue decreasing or remain below the historical average,� said USGS scientist Chris Funk. �The decreased rainfall in eastern Africa is most pronounced in the March to June season, when substantial rainfall usually occurs. Although drought is one reason for food shortages, it is exacerbated by stagnating agricultural development and continued population growth.� As the globe has warmed over the last century, the Indian Ocean has warmed especially fast. The resulting warmer air and increased humidity over the Indian Ocean produce more frequent rainfall in that region. The air then rises, loses its moisture during rainfall, and then flows westward and descends over Africa, causing drought conditions in Ethiopia and Kenya. �Forecasting precipitation variability from year to year is very difficult, and research on the links between global change and precipitation in specific regions is ongoing so that more accurate projections of future precipitation can be developed,� said University of California, Santa Barbara, scientist Park Williams. �It is also important to note that while sea-surface temperatures are expected to continue to increase in the Indian Ocean and cause an average decrease in rainfall in eastern Africa, there will still occasionally be very wet years because there are many factors that influence precipitation.� Scientists compiled existing datasets on temperature, wind speed and precipitation to see what was driving climate variations in the tropical Indian and Pacific Ocean region. Most of the Indian Ocean warming is linked to human activities, particularly greenhouse gas and aerosol emissions. The Indian Ocean has warmed especially fast because it is quickly being encroached upon by the Tropical Warm Pool, which is an area with the warmest ocean surface temperatures of anywhere on earth. This research supports efforts by the USGS and the U.S. Agency for International Development through the Famine Early Warning Systems Network. FEWS NET is a decision support system that helps target more than two billion dollars of food aid to more than 40 countries each year. Through this system, scientists are helping with early identification of agricultural drought that might trigger food insecurity.
- 12-05-2011 eco nws - global warming - impact - drought - fav - 2,300-Year Climate Record Suggests Severe Tropical Droughts as Northern Temperatures Rise - ScienceDaily (May 12, 2011) � A 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet's densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium. The researchers report in the Proceedings of the National Academy of Sciences (PNAS) that a nearly 6-foot-long sediment core from Laguna Pumacocha in Peru contains the most detailed geochemical record of tropical climate fluctuations yet uncovered. The core shows pronounced dry and wet phases of the South American summer monsoons and corresponds with existing geological data of precipitation changes in the surrounding regions. Paired with these sources, the sediment record illustrated that rainfall during the South American summer monsoon has dropped sharply since 1900 -- exhibiting the greatest shift in precipitation since around 300 BCE -- while the Northern Hemisphere has experienced warmer temperatures. Study coauthor Mark Abbott, a professor of geology and planetary science in Pitt's School of Arts and Sciences who also codesigned the project, said that he and his colleagues did not anticipate the rapid decrease in 20th-century rainfall that they observed. Abbott worked with lead author and recent Pitt graduate Broxton Bird; Don Rodbell, study codesigner and a geology professor at Union College in Schenectady, N.Y.; recent Pitt graduate Nathan Stansell; Pitt professor of geology and planetary science Mike Rosenmeier; and Mathias Vuille, a professor of atmospheric and environmental science at the State University of New York at Albany. Both Bird and Stansell received their PhD degrees in geology from Pitt in 2009. "This model suggests that tropical regions are dry to a point we would not have predicted," Abbott said. "If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet." The sediment core shows regular fluctuations in rainfall from 300 BCE to 900 CE, with notably heavy precipitation around 550. Beginning in 900, however, a severe drought set in for the next three centuries, with the driest period falling between 1000 and 1040. This period correlates with the well-known demise of regional Native American populations, Abbott explained, including the Tiwanaku and Wari that inhabited present-day Boliva, Chile, and Peru. After 1300, monsoons increasingly drenched the South American tropics. The wettest period of the past 2,300 years lasted from roughly 1500 to the 1750s during the time span known as the Little Ice Age, a period of cooler global temperatures. Around 1820, a dry cycle crept in briefly, but quickly gave way to a wet phase before the rain began waning again in 1900. By July 2007, when the sediment core was collected, there had been a steep, steady increase in dry conditions to a high point not surpassed since 1000. To create a climate record from the sediment core, the team analyzed the ratio of the oxygen isotope delta-O-18 in each annual layer of lake-bed mud. This ratio has a negative relationship with rainfall: Levels of delta-O-18 are low during the wetter seasons and high when monsoon rain is light. The team found that the rainfall history suggested by the lake core matched that established by delta-O-18 analyses from Cascayunga Cave in the Peruvian lowlands and the Quelccaya Ice Cap located high in the Andes. The Pumacocha core followed the climatological narrative of these sources between the years 980 and 2006, but provided much more detail, Abbott said. The team then established a connection between rainfall and Northern Hemisphere temperatures by comparing their core to the movement of the Intertropical Convergence Zone (ITCZ), a balmy strip of thunderstorms near the equator where winds from the Northern and Southern Hemispheres meet. Abbott and his colleagues concluded that warm Northern temperatures such as those currently recorded lure the ITCZ -- the main source of monsoons -- north and ultimately reduce the rainfall on which tropical areas rely. The historical presence of the ITCZ has been gauged by measuring the titanium concentrations of sea sediment, according to the PNAS report. High levels of titanium in the Cariaco Basin north of Venezuela show that the ITCZ lingered in the upper climes at the same time the South American monsoon was at its driest, between 900 and 1100. On the other hand, the wettest period at Pumacocha -- between 1400 and 1820, which coincided with the Little Ice Age -- correlates with the ITCZ's sojourn to far south of the equator as Northern Hemisphere temperatures cooled.
- 11-10-2011 eco nws - global warming - impact - weather - heat waves - drought - blame - can be done - Laying the Blame for Extreme Weather - ScienceDaily (Oct. 11, 2011) � Floods, tornadoes, droughts and wildfires: They are all weather-related, but blaming the latest meteorological disaster on climate change has always been a tricky matter that climate scientists have been shy to do. After all, how can you point to a specific and local event, such as a tornado or dry spell, and say it is caused by something as long-term and huge as global warming? "That's been the mantra of the community and I think it's wrong," said climate scientist Kevin Trenberth of the National Center for Atmospheric Research (NCAR) in Colorado. Trenberth and other climate scientists will be giving presentations that connect extreme weather over the past decade to climate change at a session of The Geological Society of America meeting in Minneapolis on October 11, 2011. The session, entitled Extreme Climate and Weather Events: Past, Present and Future, begins with Trenberth's presentation, The Russian Heat Wave and Other Climate Extremes of 2010. He cautions, however, that the harsh weather certainly didn't stop with 2011 and they all can be traced to the place where global warming stores its heat, year after year: the oceans. The sea surface temperatures near all the extreme flooding events of 2010 were at record levels, Trenberth explains. That includes the Caribbean, Gulf of Mexico, N. Atlantic and the Indian Ocean. "All of the storms are being formed in an environment that is warmer and wetter than before," said Trenberth. "The main thing that has happened with climate change is that you have changed the environment." Specifically, the waters are about one degree Fahrenheit warmer than pre-1970 values, leading to air that's four percent wetter. All that additional moisture and heat in the air feeds storms. "That's the climate change kicker. It's the extra nudge that indeed makes you break records." Another way of looking at it is in terms of the odds of extreme weather events. Extreme weather is always possible, after all. But with warmer oceans, such events are easier to create. "We're loading the dice in favor of extreme weather events," said Trenberth. The same goes for droughts and subsequent wild fires. They are the flip-side of the extreme storms in a global atmosphere. While unusually wet monsoons were flooding Pakistan in 2010, the same event helped to block moisture from reaching southern Russia. That led to heat waves and fires. This kind of situation reinforces cyclonic and anticyclonic patterns in the atmosphere which make some areas wetter and others drier and hotter. "So there are dynamical connections," Trenberth said. "You can't disrupt one part of the atmosphere without getting effects in the whole." And with the history and continued releases of carbon dioxide and other greenhouse gases, plus pollution into the atmosphere, there is no doubt that the system is being disrupted, he said.