Permanent Drought in the Southwestern United States

Prepared by Steven Schafersman, PhD
President, Texas Citizens for Science
2011 April 19

INTRODUCTION

The following three scientific journal papers and news reports about these three papers contain evidence for the occurrence of intense and long-lasting droughts in the southwestern United States both in the past and today as a consequence of anthropogenic global climate change. Anthropogenic climate change (ACC) is the term we use now instead of anthropogenic global warming (AGW) because--while the Earth as a whole undergoes warming and most places on the planet's surface are warming--some localities experience cooler climates. The manifestations of ACC include changes in the amount, intensity, and frequency of precipitation, changes that cause regional flooding and regional drought conditions that will persist. In many cases, the changes in rainfall as a consequence of ACC, and the droughts and flooding they cause, are potentially more troublesome and destructive for human activities than the long-term temperature changes. Thus, individual ACC deniers who state that some warming wouldn't be that harmful are neglecting the increased risks of drought and flooding that accompany ACC. Of course, just AGW itself is extremely harmful but in ways many don't consider, such as increased intensity of tropical storms, increased water shortages, biodiversity loss, and slow sea-level rise, not merely warmer temperatures.

The southwestern United States--the American Southwest--has always been relatively dry throughout human history, although rainfall has varied over thousands of years in sympathy with well-known long-term climate changes and within well-known shorter-term weather cycles. Weather cycles known as El Niño and La Niña, caused by oceanic current oscillations in the Southern Hemisphere that primarily affect the Pacific Ocean and its coasts, also affect decade-long rainfall cycles in the Southwest that have caused, for example, the droughts of the 1930s (the Dust Bowl) and 1950s. We now have scientific evidence that ACC will override the shorter-term weather cycles and create permanent drought conditions over this region of the United States. The evidence for past megadroughts in this region is now strong, and there is a broad scientific consensus based on climate modeling that ACC will drive the current Southwestern climate to another megadrought that has perhaps already begun. If this happens as expected, the future permanent climate of the American Southwest, including West Texas, will be similar to drought conditions experienced in the region in the 1930s and 1950s. If this new drought condition has already commenced, as many scientists believe, it will become stronger over the next century.

Instead of traditional rainfall amounts of 12-15 inches a year, typical of a dry grassland, rainfall amounts will permanently become 4-5 inches a year, characteristic of a fairly arid desert. This situation will create tremendous social changes as fresh water becomes even more regionally scare than it is now. The new drought climate will force lifestyle changes: turf grass lawns and large trees, which require a great deal of water to irrigate, will be banned; landscape irrigation of trees, shrubs, and flowering plants will become very restricted; homeowners will be expected to engage in rainwater harvesting and xeriscaping (landscaping with low water-tolerant plants); low-flush and dual-flush toilets will receive huge tax rebates and installation of these will soon become mandatory. Treated waste water (sewage water) will become quite valuable: it will be collected and reclaimed instead of being released to the ground, i.e., it will be treated in several steps by conventional methods and reused as irrigation water and perhaps filtered and put through a reverse osmosis system to make it perfectly suitable for human consumption. Subsurface brackish and saline waters--known as formation water, oilfield water, or connate water--will be collected and desalinated for human consumption, primarily for landscape irrigation and industrial use. Industrial scale desalination--essentially using giant building-sized RO systems--is expensive and requires a great deal of energy, although this is being done today with seawater in places where freshwater is scarce and energy is cheap, such as in Middle Eastern petroleum-rich countries. This water can ultimately be purified to use as drinking water if needed. Large-scale agricultural irrigation, common today in dry regions even though it damages the soil by making it salty, will cease because the aquifers will have become exhausted, damaged, or the remaining water they contain will become too valuable to waste on agricultural irrigation.

The most recent study predicts that the tropics and much of the Northern Hemisphere will experience an irreversible rise in summer temperatures within 20-60 years as atmospheric greenhouse gas concentrations continue to increase. Many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades. Middle latitudes of Europe, China and North America – including the United States – are likely to undergo extreme summer temperature shifts within 60 years, the researchers found. According to the study's projections, "large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years." This dramatic shift in seasonal temperatures could have severe consequences for human health, agricultural production, and ecosystem productivity. It will also occasion shifts in human populations as citizens migrate to cooler climates. Perhaps the most obvious change will be dramatic and degrading landscape, environmental, and biodiversity alterations.

I am posting on this page links to three scientific papers that forecast permanent, severe drought in the American Southwest and news reports that accompanied their publication. The affected region includes the whole of Texas which is currently experiencing a major, severe drought. The three papers indicate, and I agree, that the current Texas drought--which is forecast to continue next year in a form as extreme as 2011 before conditions abate somewhat when the El Niño weather cycle returns--is merely the first step toward a new permanent drought climate. As a scientist, I have access to digital versions of these original papers and I am am making the three of them easily available to the public. Citizens in Texas need to be aware of the dangers they face in the coming decades. Following the climate models and projections presented in these science journal articles, I predict that the drought we are experiencing this year will only partially ameliorate and quickly return in an even more severe and long-lasting form. I live in West Texas and we are experiencing a water shortage now (due to poor planning by regional authorities who did not have the scientific foresight, competence, or attitude to understand global climate change and excessive human population growth and do something about it). The regional water shortage will soon become much worse and even debilitating. Despite the abundant evidence for this prognosis, most citizens living in West Texas--and this especially includes political leaders--continue to deny the facts before their eyes. Most are climate change denialists; this group includes public officials and leaders in the petroleum industry, our largest local industry. They will probably continue to be denialists as they are forced to make major life style changes without understanding why.

CONTENTS

Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America
by Richard Seager, and others
Science, v. 316, p. 1181-1184, 25 May 2007

Extended megadroughts in the southwestern United States
by Peter J. Fawcett, and others
Nature, v. 470, p. 518-521, 24 February 2011

Observational and model evidence of global emergence of permanent, unprecedented heat in the 20th and 21st centuries
by Noah Diffenbaugh and Martin Scherer
Climatic Change Letters, v. 107, n. 3-4, p. 615-624, 7 June 2011


ORIGINAL SCIENTIFIC PAPER:

Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America (pdf, 1.4 MB)
by Richard Seager, and others
Science, v. 316, p. 1181-1184, 25 May 2007

Abstract

How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for the allocation of water resources and the course of regional development. Here we show that there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a time frame of years to decades.

NEWS REPORTS:

http://www.scientificamerican.com/article.cfm?id=southwest-america-drying-climate&ref=rss

Dust Bowl 2.0: Is the Southwest Drying Up?

New research shows that the current drought plaguing the American West is likely the beginning of a new trend brought on by global warming.

By Nikhil Swaminathan
Scientific American
Thursday, April 5, 2007


PAST IS FUTURE:
The dry landscape in this image,
taken during the drought on the Great Plains in the
1930s, could be what lies ahead for the southwestern
region of the United States and northern Mexico.


In his much-ballyhooed 1939 novel, The Grapes of Wrath, John Steinbeck describes the conditions of the southern American Great Plains, where a severe drought caused the devastating wind-swept storms of the 1930s dust bowl: "When June was half gone, the big clouds moved up out of Texas and the Gulf, high heavy clouds, rain-heads," Steinbeck wrote. "The rain-heads dropped a little spattering and hurried on to some other country. Behind them the sky was pale again and the sun flared. In the dust there were drop craters where the rain had fallen, and there were clean splashes on the corn, and that was all."

Unfortunately, severe droughts are not just the stuff of classic literature. A research team, led by a group at Columbia University's Lamont-Doherty Earth Observatory (LDEO) in Palisades, N.Y., reveal in this week's Science that southwestern North America will likely be saddled with increasingly arid conditions during the next century. This drying effect, the researchers say, is directly related to man-made climate change and will demand new methods for managing water resources in the region. They based their findings on 19 climate models, all of which contributed to the Intergovernmental Panel on Climate Change's (IPCC) Fourth Assessment Report released in Paris in early February.

"The Southwest," in the current study, refers to the southwestern U.S. and northern Mexico. The researchers add that a similar pattern of drying is predicted for the region bounded by southern Europe, the Mediterranean Sea and the Middle East; wetter climes are expected for areas farther away from the tropics and closer to Earth's poles.

The output of the climate models used in the current analysis came in measures of future precipitation and evaporation. "[Those figures are] what matters in terms of the water that's available to the soil in the ground," says study co-author Mingfang Ting, a senior research scientist at LDEO. By subtracting the area's evaporation rate from its precipitation rate, the scientists were able to make projections on the net gain of water available in the ground. (Of the 19 models, 18 of them show this value to be negative by the latter half of the current century, indicating, according to Ting, that "precipitation is reduced or evaporation could be increased.")

On average, the models suggest that the cusp of the late 20th century–early 21st century ushered in a period of consistently arid climate. Soon, if not already, one quarter of the models predict that moisture will begin to disappear from the region at a rate of 0.1 millimeters per day. In fact, the researchers believe the current six-to-seven-year drought in the region is the beginning of this drying trend. "The current drought is related to the warming due to the greenhouse gases," says Ting. "In the past, El niño [would] disappate the drought, but now it's not able to stop the drought.''

Normally, the El Niño and La Niña weather systems are largely responsible for cyclical precipitation and drought in the Southwest. El Niño brings in moisture from the tropics (by the warming of the ocean, which condenses water into the lower atmosphere that is then shuttled into the subtropical regions), whereas La Niña essentially does the opposite, causing cold ocean temperatures in the equatorial eastern Pacific. The latter phenomenon is believed to be the culprit behind both the 1930s dust bowl and a widespread drought in the Southwest during the 1950s.

"The drought that we're taking about is not La Niña," Ting explains, referring to the current dry system. "That is associated with the greenhouse gas warming." While the consequences are similar, the actual effect on the oceans is very different, she says. Instead of a cooling in the tropics, there will be a uniform warming of the ocean, which will push the Pacific jet stream farther north. As a result, "Canada does get quite a lot more rain," Ting notes, whereas "the whole state of California, for example, will be much drier."

"There will be a new climatology that is like a permanent drought," says Ting. "It really is a severe problem in terms of managing water resources." Tapio Schneider, an assistant professor of environmental science and engineering at Caltech, points out that these findings and projections are consistent across all subtropical regions, such as in Australia, which is also suffering from droughtlike conditions. He also notes that water issues are already being addressed. "There are people in government that are worrying about this," he says, "and have been worrying about this for awhile."

Just last week, California Gov. Arnold Schwarzenegger reiterated his proposal that his state set aside $5.9 billion to better manage its water resources. "Water infrastructure is no different than when we talk about transportation infrastructure or the infrastructure in our building more schools," he said at a press conference. "As we see an increase in population we must build more. We must build more roads, we must build more schools and we must build more above-the-ground water storage."

============

http://articles.latimes.com/2007/apr/06/science/sci-swdrought6

http://livingrivers.org/archives/article.cfm?NewsID=765

A permanent drought seen for Southwest

A study says global warming threatens to create another Dust Bowl. Water politics could also get heated.

Alan Zarembo and Bettina Boxall
Los Angeles Times Staff Writers
April 06, 2007

The driest periods of the last century -- the Dust Bowl of the 1930s and the droughts of the 1950s -- may become the norm in the Southwest United States within decades because of global warming, according to a study released Thursday.

The research suggests that the transformation may already be underway. Much of the region has been in a severe drought since 2000, which the study's analysis of computer climate models shows as the beginning of a long dry period.

The study, published online in the journal Science, predicted a permanent drought by 2050 throughout the Southwest -- one of the fastest-growing regions in the nation.

The data tell "a story which is pretty darn scary and very strong," said Jonathan Overpeck, a climate researcher at the University of Arizona who was not involved in the study.

Richard Seager, a research scientist at Lamont-Doherty Earth Observatory at Columbia University and the lead author of the study, said the changes would force an adjustment to the social and economic order from Colorado to California.

"There are going to be some tough decisions on how to allocate water," he said. "Is it going to be the cities, or is it going to be agriculture?"

Seager said the projections, based on 19 computer models, showed a surprising level of agreement. "There is only one model that does not have a drying trend," he said.

Philip Mote, an atmospheric scientist at the University of Washington who was not involved in the study, added, "There is a convergence of the models that is very strong and very worrisome."

The future effect of global warming is the subject of a United Nations report to be released today in Brussels, the second of four installments being unveiled this year.

The first report from the Intergovernmental Panel on Climate Change was released in February. It declared that global warming had become a "runaway train" and that human activities were "very likely" to blame.

The landmark report helped shift the long and rancorous political debate over climate change from whether man-made warming was real to what could be done about it.

The mechanics and patterns of drought in the Southwest have been the focus of increased scrutiny in recent years.

During the last period of significant, prolonged drought -- the Medieval Climate Optimum from about the years 900 to 1300 -- the region experienced dry periods that lasted as long as 20 years, scientists say.

Drought research has largely focused on the workings of air currents that arise from variations in sea-surface temperature in the Pacific Ocean known as El Nino and La Nina.

The most significant in terms of drought is La Nina. During La Nina years, precipitation belts shift north, parching the Southwest.

The latest study investigated the possibility of a broader, global climatic mechanism that could cause drought. Specifically, they looked at the Hadley cell, one of the planet's most powerful atmospheric circulation patterns, driving weather in the tropics and subtropics.

Within the cell, air rises at the equator, moves toward the poles and descends over the subtropics.

Increasing levels of greenhouse gases, the researchers said, warms the atmosphere, which expands the poleward reach of the Hadley cell. Dry air, which suppresses precipitation, then descends over a wider expanse of the Mediterranean region, the Middle East and North America.

All of those areas would be similarly affected, though the study examined only the effect on North America in a swath reaching from Kansas to California and south into Mexico.

The researchers tested a "middle of the road" scenario of future carbon dioxide emissions to predict rainfall and evaporation. They assumed that emissions would rise until 2050 and then decline. The carbon dioxide concentration in the atmosphere would be 720 parts per million in 2100, compared with about 380 parts per million today.

The computer models, on average, found about a 15% decline in surface moisture -- which is calculated by subtracting evaporation from precipitation -- from 2021 to 2040, as compared with the average from 1950 to 2000.

A 15% drop led to the conditions that caused the Dust Bowl in the Great Plains and the northern Rockies during the 1930s.

Even without the circulation changes, global warming intensifies existing patterns of vapor transport, causing dry areas to get drier and wet areas to get wetter. When it rains, it is likely to rain harder, but scientists said that was unlikely to make up for losses from a shifting climate.

Kelly Redmond, deputy director of the Western Regional Climate Center in Reno, who was not involved in the study, said he thought the region would still have periodic wet years that were part of the natural climate variation.

But, he added, "In the future we may see fewer such very wet years."

Although the computer models show the drying has already started, they are not accurate enough to know whether the drought is the result of global warming or a natural variation.

"It's really hard to tell," said Connie Woodhouse, a paleoclimatologist at the University of Arizona. "It may well be one of the first events we can attribute to global warming."

The U.S. and southern Europe will be better prepared to deal with frequent drought than most African nations.

For the U.S., the biggest problem would be water shortages. The seven Colorado River Basin states -- Colorado, Wyoming, Utah, Nevada, New Mexico, Arizona and California -- would battle each other for diminished river flows.

Mexico, which has a share of the Colorado River under a 1944 treaty and has complained of U.S. diversions in the past, would join the struggle.

Inevitably, water would be reallocated from agriculture, which uses most of the West's supply, to urban users, drying up farms. California would come under pressure to build desalination plants on the coast, despite environmental concerns.

"This is a situation that is going to cause water wars," said Kevin Trenberth, a scientist at the National Center for Atmospheric Research in Boulder, Colo.

"If there's not enough water to meet everybody's allocation, how do you divide it up?"

Officials from seven states recently forged an agreement on the current drought, which has left the Colorado River's big reservoirs -- Lake Powell and Lake Mead -- about half-empty. Without some very wet years, federal water managers say, Lake Mead may never refill.

In the next couple of years, water deliveries may have to be reduced to Arizona and Nevada, whose water rights are second to California.

---------------

Press Release from Lamont-Doherty Earth Observatory

New Study Shows Climate Change Likely to Lead to Periods of Extreme Drought in Southwest North America

How anthropogenic climate change will impact the arid regions of Southwestern North America has implications for the allocation of water resources and the course of regional development. The findings of a new study, appearing in Science, show that there is a broad consensus amongst climate models that this region will dry significantly in the 21st Century and that the transition to a more arid climate may already be underway. If these models are correct, the levels of aridity of the recent multiyear drought, or the Dust Bowl and 1950s droughts, will, within the coming years to decades, become the new climatology of the American Southwest.

The study’s findings have implications on policies and decision making that protects the region from such extreme climate conditions. “'The arid lands of southwestern North America will imminently become even more arid as a result of human-induced climate change just at the time that population growth is increasing demand for water, most of which is still used by agriculture,” said Richard Seager, Senior Research Scientist at the Lamont-Doherty Earth Observatory and one of the lead authors of the study. “The West, and in particular, the United States and Mexico, need to plan for this right now, coming up with new, well-informed and fair deals for allocation of declining water resources.”

Projections of anthropogenic, or man-made, climate change conducted by 19 different climate modeling groups around the world, using different climate models, show widespread agreement that Southwestern North America—and the subtropics in general—are heading toward a climate even more arid than now. The models show that human-induced aridification becomes marked early in the current century. In the Southwest the levels of aridity seen in the 1950s multiyear drought, or the 1930s Dust Bowl, become the new climatology by mid-century: a perpetual drought.

According to the study, as the planet warms, the Hadley Cell, which links together rising air near the Equator and descending air in the subtropics, expands poleward. Descending air suppresses precipitation by drying the lower atmosphere so this process expands the subtropical dry zones. At the same time, and related to this, the rain-bearing mid-latitude storm tracks also shift poleward. Both changes in atmospheric circulation, which are not fully understood, cause the poleward flanks of the subtropics to dry.

In contrast to historical droughts, future drying is not linked to any particular pattern of change in sea surface temperature but seems to be the result of an overall surface warming driven by rising greenhouse gases. Evidence for this is that subtropical drying occurs in atmosphere models alone when they are subjected to uniform increases in surface temperature. “Our study emphasizes the fact that global warming not only causes water shortage through early snow melt, which leads to significant water shortage in the summer over the Southwest, but it also aggregates the problem by reducing precipitation," said Mingfang Ting, Doherty Senior Research Scientist also at Lamont-Doherty and one of the study’s co-authors.

Drying of arid lands in the southwestern United States and northern Mexico will have important consequences for water resources, regional development and cross border relations and migration. According to the models the drying should already be underway and, over the length of time it takes to plan significant changes in water resource engineering and allocation (years to a few decades), will become well established.

The study also shows that, in addition to the Southwestern North America other land regions to be hit hard by subtropical drying include southern Europe, North Africa and the Middle East as well as parts of South America.

The study was conducted in close collaboration with scientists at the NOAA Geophysical Fluid Dynamics Laboratory. This collaboration emphasizes the close ties between Columbia University and NOAA that has developed since the establishment of the NOAA Cooperative Institute for Climate Applications and Research at Lamont in 2003.

============

http://www.ucar.edu/communications/staffnotes/0705/drought.shtml

May 2007

Study predicts permanent drought in Southwest


The swath of North America between Kansas, California,
and northern Mexico can expect long-term drought conditions
in the future due to warming global temperatures. The Southwest
is already stressed from a drought that has affected the region
since 1999. Here, an arroyo in northern Mexico sits dry.


Aridity has always been the defining feature of the American Southwest, even as large-scale hydraulic engineering has allowed cities such as Phoenix and Las Vegas to burst from the desert floor.

But according to a sobering new study, the Southwest’s aridity is about to get worse. Published in the April 9 issue of Science, “Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America” predicts that climate change will permanently alter the landscape of the Southwest so severely that conditions reminiscent of the Dust Bowl days of the 1930s could become the norm within a few decades.

“Our study suggests a perpetual arid condition over the American Southwest,” says Jian Lu, a postdoctoral researcher in ASP/CGD who is an author of the study.

Of the 19 different computer models that the research team used for the study, all but one showed a drying trend in the swath of North America between Kansas, California, and northern Mexico. The models predicted an average 15% decline in runoff for the Southwest between 2021 and 2040, compared to the average surface moisture between 1950 and 2000.

The Southwest’s future droughts are expected to be of a different nature than those that have afflicted the region in the past. Scientists attribute past droughts to variations in sea surface temperatures caused by El Niño and La Niña events in the Pacific Ocean. La Niña is especially influential as it tends to shift precipitation belts north, leaving the Southwest thirsty.

As the climate warms, however, the basic dynamics of the atmosphere change, particularly in regard to the Hadley cell, a powerful circulation pattern that drives weather in the tropics and subtropics. “Our confidence in our projection is built upon our understanding of the fundamental dynamics of the Hadley cell,” Jian says.

Warm, moist air from near the equator normally rises into the atmosphere until it reaches the stratosphere, the second layer of Earth’s atmosphere. The air then spreads north and south toward the poles, descends over the subtropics, and flows back toward the Equator in the form of trade winds, completing the cell. Because the descending air over the subtropics suppresses rain by drying the lower atmosphere, many of Earth’s great deserts are located in these regions.

As the atmosphere warms from climate change, scientists expect the Hadley cell to expand its reach, bringing hot, dry air to a larger swath of the Middle East, Mediterranean, and North America, including the Southwest. “In the future warmed climate,” Jian explains, “the Hadley cell and the subtropical high should expand poleward, which tends to block rain coming through from the Pacific.”

For the study, the research team assumed that greenhouse gases would continue to rise from today’s level of 380 parts per million until beginning a decline around 2050, measuring 720 parts per million in 2100.

Jian stresses that it’s difficult to predict the onset or magnitude of the drought. “The timing of the drought is very uncertain, and given the uncertainties in the model physics and sizable spread across different models, we are not very sure about the magnitude of drought in the future,” he says.

The Southwest is one of the fastest-growing regions in the country. Increased aridity would put enormous strain on the Colorado River, a lifeline for the seven states in its basin (Colorado, Utah, Wyoming, Nevada, New Mexico, Arizona, and California) and northern Mexico.

Already, the region is experiencing changes that scientists link to climate change, including more severe wildfires, earlier winter snowmelt, the destruction of heat-weakened trees by beetles, and a loss of biodiversity in southern Arizona’s high-elevation “sky islands.”

================

http://www.sott.net/articles/show/215067-Permanent-Drought-Predicted-for-American-Southwest

'Permanent Drought' Predicted for American Southwest

Seth Shulman
Grist
Thu, 12 Aug 2010

If you're one of the tens of millions of people who live in the southwestern United States, get ready for drier weather. That's the message from Richard Seager, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory. The American Southwest, says Seager, is soon likely to experience a "permanent drought" condition on par with the Dust Bowl of the 1930s.

That rather frightening prediction is the most likely scenario for the region, given the global warming now underway. "It is a matter of simple thermodynamics," says Seager. "The region will face a considerable increase in aridity over the coming decade."

The Southwest is as dry as it is because the local atmospheric flow tends to export far more moisture than storms can carry into the region. This is the case in other parts of the so-called subtropics, those areas directly north and south of the equatorial tropics. But as earth's atmosphere becomes laden with heat-trapping greenhouse gases, it will be able to retain even more moisture. That means more evaporation from lakes and rivers, more moisture loss from plants, and drier soil.

A critical player in this drying cycle is the planetary-scale circulation system known as the "Hadley cell." This vast atmospheric system links rising air near the Equator with descending air in the subtropics, giving rise to the subtropical jet streams.

In the northern hemisphere the jet stream flows west to east across North America. Rising moist air condenses and forms thunderstorms in the tropics, but the moisture is largely lost by the time the air descends at subtropical latitudes. That's why most of the world's deserts are situated in the subtropics.

The Hadley cell is growing. Its expansion above a larger swath of the American Southwest, along with a shifting of the jet stream and many storms northward, is a worrisome trend, says Seager. It means there is little chance that the Southwest can avoid becoming drier in the coming decades. In fact, when Seager's team analyzed some 49 computer projections of the region's likely future climate, using 19 major climate models, all but three scenarios agreed: drought ahead.

Seager has been tracking changes in precipitation for nearly a quarter century. For his graduate thesis at Columbia University he used computer models to try and understand the role of sea-surface temperatures in driving precipitation patterns in the tropics and around the world.

Growing up in a working-class family in Norwich, England, Seager spent a lot of time outdoors with his family. Cycling and hiking the hills of England and Scotland sparked his interest in the physical world. It didn't hurt his current professional interests that he grew up with "more weather than you would wish on anyone."

One of his undergraduate tutors was the climate scientist Ann Henderson-Sellers. She had recently returned to England after working in James Hansen's renowned climate science research center in New York. "She's the one who suggested that I apply to graduate school in climate science in the U.S.," says Seager. He and his brother were the first members of their family to earn college degrees.

Moving to New York for a graduate degree was a big step -- and, as it turned out, a lasting one. Except for a stint as a postdoc at the University of Washington in Seattle, Seager has remained at Columbia to conduct climate research ever since.

Seager recognizes that the stakes of his drought research are high. "The prospect of a drought on par with the 1930s is a matter of serious concern," he says. "With some two million people displaced, the Dust Bowl was probably the worst environmental disaster in the nation's history -- even counting the current oil spill in the Gulf."

Seager is quick to add, however, that many features of the Dust Bowl are unlikely to be repeated. For one thing, he says, "we have learned an awful lot about soil conservation since the 1930s."

As severe as the impending drought conditions now appear, Seager also emphasizes the vital mitigating role played by the Colorado River, which carries an enormous volume of water to the southwestern United States. The region, he notes, now diverts between 80 and 90 percent of that water for agricultural uses, but that could be changed.

Other regions are not as lucky. The Colorado River is barely a trickle of water by the time it reaches the border with northern Mexico, where the potential for water shortages is more immediate and more likely to lead to the displacement of people in coming years.

Seager believes that part of his job is to inform people about these climatic changes. He often briefs water managers throughout the region, including those with the California Department of Water Resources and at the U.S. Bureau of Reclamation, which manages the Colorado River.

"It's a comparatively small part of my job, because mostly I'm focused on doing the science," Seager says, "but it is an important part. Much of our funding comes from the National Oceanic and Atmospheric Administration (NOAA), and a reasonable condition of the grants is that we do something to make sure the information gets out."

One common complaint is that his work is neither precise enough nor at a large enough scale to be useful to water managers. He feels their pain. "There is still so much natural variability in the weather that I cannot say with certainty what will happen in their particular neck of the woods and exactly when," he says. But he is hard at work trying to improve his modeling of the region's climate.

For the past several years Seager has been studying naturally occurring droughts in the American Southwest all the way back to the Middle Ages. The man-made forces that are driving today's climate change are clear, he says. But the extent to which naturally occurring cycles might mitigate or exacerbate the impending drought remain uncertain.

"When I first went into this field, it had little perceived practical relevance," says Seager. "The field has developed rapidly to a point where it can offer practical predictions, and the goal now is to make these as precise as we possibly can."

Water managers in the Southwest seem to be paying attention, and even taking action. "They understand that it's going to get drier," says Seager. "So it is probably not a good idea for them to sit around and wait until our models get better."


ORIGINAL SCIENTIFIC PAPER:

Extended megadroughts in the southwestern United States (pdf)
by Peter J. Fawcett, and others
Nature, v. 470, p. 518-521, 24 February 2011

Abstract

The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, ‘dust-bowl-like’ megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C4 plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ~2°C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4–6°C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase.

NEWS REPORTS:

http://www.nature.com/news/2011/110223/full/news.2011.120.html

Mega-drought threat to US Southwest

Global warming could tip region towards repeat of Pleistocene events.


Quirin Schiermeier
Nature
Published online 23 February 2011


The southwestern US may have to get
used to an ever drier future.


The Dust Bowl — the seven-year drought that devastated large swathes of US prairie land in the 1930s — was the worst prolonged environmental disaster recorded for the country. But a study of the American Southwest's more distant climatic past reveals that the catastrophic drought was a mere dry spell compared to the 'mega-droughts' that were recurring long before humans began to settle the continent.

The findings, reported in a paper in Nature1 this week, add to concerns that the already arid region might face quasi-permanent drought conditions as climate continues to warm.

The team, led by Peter Fawcett, a climate scientist at the University of New Mexico in Albuquerque, reconstructed the region's climate history using geochemical indicators from an 82-metre-long lake sediment core from the Valles Caldera in northern New Mexico. Analysis of climate and vegetation proxies, such as pollen and carbon-isotope ratios, suggests that the Southwest experienced abrupt and surprisingly pronounced climate shifts during warm periods of the Pleistocene, including transitions to extended dry periods that lasted for hundreds or even thousands of years.

Reliving the past

If today's climate repeated past patterns, the southwestern United States might move into a wetter and cooler phase. Such a transition happened at one point during the so-called Marine Isotope Stage (MIS) 11, an interglacial period around 400,000 years ago that shows some striking parallels with the Holocene, our current warm period. This seems to have roughly advanced to the point at which the climate in MIS 11 began to switch to a less arid one.

Earth's orbit and axal tilt during the unusually long MIS 11 stage was similar to orbital conditions during the Holocene, which scientists think will last longer than most Pleistocene warm periods.

But for all the similarities, the climate during MIS 11 was unperturbed by human activity. This time around, rising greenhouse-gas concentrations driven by human activity will very likely override any natural cooling trend. Scientists fear that the Southwestern climate may in fact switch to an extended dry mode such as the ones that occurred during particularly warm Pleistocene periods.

"We won't know for sure if it happens again until we get there," says Fawcett. "But we are certainly increasing the possibility of crossing a critical threshold to severe and lasting drought conditions."

Sudden shifts in carbon isotopes and lowered total organic carbon in the sediment record suggest that grasses and shrubs that depend mostly on summer rain died out during extended Pleistocene droughts. This is surprising, says Fawcett, because summer monsoon rainfall was thought to become more intense in a warmer climate. That summer rain was in fact strongly reduced, or had almost stopped, suggests that regional climate patterns must have shifted radically when Pleistocene temperatures crossed a threshold.

"The scary thing is that we seem to be very close to this point again," he says.

A dry future

The Southwest has experienced significant reductions in rainfall during the last decade, causing freshwater reservoirs and groundwater to fall to unusually low levels. Colorado River flows recorded at Lees Ferry, Arizona, from 2000 to 2009 are the lowest on record.

Climate models suggest that the region will in future become even drier as atmospheric circulation patterns change and subtropical dry zones expand towards the poles2.

"The drying we expect for the twenty-first century is entirely the result of increased greenhouse forcing," says Richard Seager, a climate researcher at the Lamont-Doherty Earth Observatory in Palisades, New York. "Any natural variations in orbital forcing and incoming sunlight will hardly have a noticeable role in the near future."

A 10–15% reduction in rainfall is enough to cause severe drought in the region, he says. Meanwhile, debate continues among scientists whether a transition to quasi-permanent dry conditions is imminent or already underway, and to what extent global warming has increased the risk of drought.

"A signal of anthropogenic drying is emerging, but it is still small," says Seager. "I'd expect that by mid-century the human signal will exceed the amplitude of natural climate variability. Then we can safely say that the Southwest has entered a new climate stage."

References

1. Fawcett, P. et al. Nature 470, 518-521 (2011).
2. Seager, R. et al. Science 316, 1181-1184 (2007).

==============

http://green.blogs.nytimes.com/2011/02/25/a-future-mega-drought-in-the-southwest/

Does the Southwest Face a Mega-Drought?

By JOHN COLLINS RUDOLF
New York Times
February 25, 2011

Rising global temperatures resulting from emissions of human origin could tip the southwestern United States into a period of prolonged extreme drought seen before only in distant geological history, a new study suggests.
Lake sediment taken from the Valles Caldera, above, revealed “megadroughts” lasting as long as 1,000 years.

Researchers dug deep into the region’s climate history by studying a 270-foot core of lake sediment taken from the Valles Caldera, a volcanic depression in northern New Mexico. Data extracted from the core revealed “mega-droughts” in the region lasting as long as a thousand years.

For parallels to the planet’s current climate, the researchers focused on interglacial periods, when ice ages caused by small irregularities in the Earth’s orbit around the sun gave way to periods of warmth and glacial retreat. The current epoch, the Holocene, is the most recent interglacial period.

If the current epoch followed past trends, the Southwest would eventually enter a cooler, wetter phase, the researchers found. But that was without considering changes in the global climate that are expected to arise from steadily rising concentrations of carbon dioxide and other greenhouse gases.

This added warmth could tip the Southwest into an era of continued severe drought potentially lasting a millennium or more, said Peter Fawcett, a climate scientist at the University of New Mexico in Albuquerque who led the study.

“We won’t know for sure if it happens again until we get there,” Dr. Fawcett told Nature News. “But we are certainly increasing the possibility of crossing a critical threshold to severe and lasting drought conditions.”

“The scary thing is that we seem to be very close to this point again,” he added.

The study appears in this week’s edition of the scientific journal Nature.

===============

http://content.usatoday.com/communities/sciencefair/post/2011/02/megadroughts-southwest-global-warming-climate-change/1

Megadroughts once reigned supreme in Southwest -- and may again

By Doyle Rice
USA TODAY
Feb 25, 2011

Something else to worry about over the weekend:

As the southern tier of the USA suffers through a drought that stretches from Arizona to Virginia – a distance of some 2,000 miles – new research this week finds that "megadroughts" used to be a common feature of the southwestern USA, and may be again, thanks to our favorite villain, climate change.

These "megadroughts" lasted for, um, millennia, which I think is a long, long time.

The authors, in a study published this week in the British journal Nature, say that "megadroughts" were a regular feature of Pleistocene interglacial periods in the Southwest, which were some 370,000 to 550,000 years ago. The study suggests that if it wasn't for man-made climate change, this region would probably now be entering a cooler, wetter phase.

The Southwest is known to have endured decades-long droughts over the past two millennia, but it has been unclear whether there were longer "megadroughts," lasting for hundreds or thousands of years, and if so, how regular and intense they were.

Peter Fawcett of the University of New Mexico and his co-authors analyzed a lake sediment core from Valles Caldera, N.M., and determined that these megadroughts, which had profound effects on water availability and ecosystems, were caused by the poleward expansion of the subtropical dry zone, in response to natural climate warming.

This climatic mechanism is similar to that predicted for the southwestern USA as a result of man-made global warming, and these extremely dry Pleistocene periods may therefore suggest future climate change in the region.

As the authors note in their article, these future permanent, 'dust-bowl-like' megadrought conditions, lasting decades to a century, are predicted as a consequence of global warming.

[In the 43 comments to this brief note, many climate change deniers took the time to write long, detailed rants.]


ORIGINAL SCIENTIFIC PAPER:

Observational and model evidence of global emergence of permanent, unprecedented heat in the 20th and 21st centuries (pdf, 5.6 MB)
by Noah Diffenbaugh and Martin Scherer
Climatic Change Letters, v. 107, n. 3-4, p. 615-624, 7 June 2011



NEWS REPORTS:

http://news.stanford.edu/news/2011/june/permanent-hotter-summers-060611.html

http://www.worldweatherpost.com/2011/06/06/stanford-climate-scientists-forecast-permanently-hotter-summers

Stanford climate scientists forecast permanently hotter summers beginning in 20 years

Large areas of the globe are likely to warm up so quickly that by the middle of this century even the coolest summers will be hotter than the hottest summers of the past 50 years.


Increased greenhouse gas emissions could lead to permanently
hotter summers in coming decades, according to Stanford scientists.


BY Donna Hesterman
Stanford University News
Stanford Report, June 6, 2011

The tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures within the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase, according to a new climate study by Stanford University scientists. The results will be published later this month in the journal Climatic Change Letters.

In the study, the Stanford team concluded that many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades. Middle latitudes of Europe, China and North America – including the United States – are likely to undergo extreme summer temperature shifts within 60 years, the researchers found.

"According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said the study's lead author, Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford. The study is co-authored by Stanford research assistant Martin Scherer.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" Diffenbaugh said. "That got us thinking – at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?"

Climate models, past and future

To determine the seasonal impact of global warming in coming decades, Diffenbaugh and Scherer analyzed more than 50 climate model experiments –including computer simulations of the 21st century when global greenhouse gas concentrations are expected to increase, and simulations of the 20th century that accurately "predicted" the Earth's climate during the last 50 years. The analysis revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years.

"We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun," Diffenbaugh said. "It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well."

According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest. "We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the authors wrote.

Tropical regions may see the most dramatic changes first, but wide swaths of North America, China and Mediterranean Europe are also likely to enter into a new heat regime by 2070, according to the study.

Environmental Impact

This dramatic shift in seasonal temperatures could have severe consequences for human health, agricultural production and ecosystem productivity, Diffenbaugh said. As an example, he pointed to record heat waves in Europe in 2003 that killed 40,000 people. He also cited studies showing that projected increases in summer temperatures in the Midwestern United States could reduce the harvest of staples, such as corn and soybeans, by more than 30 percent.

Diffenbaugh was surprised to see how quickly the new, potentially destructive heat regimes are likely to emerge, given that the study was based on a relatively moderate forecast of greenhouse gas emissions in the 21st century.

"The fact that we're already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded," Diffenbaugh said.

The research was supported by the National Science Foundation, the Department of Energy, the National Institutes of Health and the World Bank.

Donna Hesterman is a science-writer intern at the Woods Institute for the Environment.

==========

http://www.sciencedaily.com/releases/2011/06/110606113405.htm

Climate Scientists Forecast Permanently Hotter Summers


A new study finds that the tropics and much of the Northern Hemisphere
are likely to experience an irreversible rise in summer temperatures within
the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase.


ScienceDaily (June 6, 2011) — The tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures within the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase, according to a new climate study by Stanford University scientists.

The results will be published later this month in the journal Climatic Change.

In the study, the Stanford team concluded that many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades. Middle latitudes of Europe, China and North America -- including the United States -- are likely to undergo extreme summer temperature shifts within 60 years, the researchers found.

"According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said the study's lead author, Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford. The study is co-authored by Stanford research assistant Martin Scherer.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" Diffenbaugh said. "That got us thinking -- at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?"

Climate models, past and future

To determine the seasonal impact of global warming in coming decades, Diffenbaugh and Scherer analyzed more than 50 climate model experiments -including computer simulations of the 21st century when global greenhouse gas concentrations are expected to increase, and simulations of the 20th century that accurately "predicted" Earth's climate during the last 50 years. The analysis revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years.

"We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun," Diffenbaugh said. "It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well."

According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest. "We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the authors wrote.

Tropical regions may see the most dramatic changes first, but wide swaths of North America, China and Mediterranean Europe are also likely to enter into a new heat regime by 2070, according to the study.

Environmental impact

This dramatic shift in seasonal temperatures could have severe consequences for human health, agricultural production and ecosystem productivity, Diffenbaugh said. As an example, he pointed to record heat waves in Europe in 2003 that killed 40,000 people. He also cited studies showing that projected increases in summer temperatures in the Midwestern United States could reduce the harvest of staples, such as corn and soybeans, by more than 30 percent.

Diffenbaugh was surprised to see how quickly the new, potentially destructive heat regimes are likely to emerge, given that the study was based on a relatively moderate forecast of greenhouse gas emissions in the 21st century.

"The fact that we're already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded," Diffenbaugh said.

The research was supported by the National Science Foundation, the Department of Energy, the National Institutes of Health and the World Bank.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Stanford University. The original article was written by Donna Hesterman, science-writer intern at the Woods Institute for the Environment.

==========

http://news.discovery.com/earth/extreme-heat-the-new-norm.html

Extreme Heat the New Norm

Analysis by Tim Wall
Discovery News
Wed Jun 8, 2011

The hottest summer day you remember from childhood could be the norm in a few decades; in fact it looks like the heat has already been cranked up.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" said Noah Diffenbaugh, an assistant professor of environmental Earth system science at Stanford, in a press release.

"That got us thinking –- at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?" wondered Diffenbaugh.

Diffenbaugh is lead author of a study to be published later this month in the journal Climate Change. Stanford research assistant Martin Scherer co-authored the study.

"According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said Diffenbaugh.

Within the next 20 to 60 years, if greenhouse gas levels continue to rise, summer temperatures are likely to rise irreversibly around the globe, with the tropics feeling the heat first, and parts of Africa, Asia and the Americas suffering unprecedented summer heat within the next two decades, according to Diffenbaugh's study. The middle latitudes, including Europe, China and the United States, will feel the heat within 60 years, they report.

But evidence suggests that these summer heat extremes are already happening.

"We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun," Diffenbaugh said. "It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well."

The authors point to the tropics as the poster child for increased summer heat.

"We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the authors wrote.

"The fact that we're already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded," Diffenbaugh said.

Diffenbaugh and Scherer based their predictions on more than 50 climate model experiments. By looking at models that represented the behavior of the worlds' temperatures over the last half century, as well as models for how temperatures will change in the future, the researchers forecast that much of the world will experience a permanent increase in seasonal temperatures within 60 years.

The models were based on relatively moderate forecasts of greenhouse gas emissions for the 21st century.

===========

http://news.discovery.com/earth/summer-heat-waves.html

Summer Heat Waves to Increase

This summer's record heat waves are just a taste of things to come.


More stifling summer heat waves are in our
future with the onset of global warming.


By Larry O'Hanlon
Discovery News
Tue Sep 14, 2010

THE GIST
- Summer heat waves are already ramping up with global warming.
- Limiting global warming to 2 degrees C may not be enough to stop more extreme heat events.
- The 2010 summer's heat waves in the U.S. Northeast, Russia and Japan were all caused by global warming.

Record summer heat waves are already happening more often and will get even hotter and more frequent over the next 30 years, predict scientists who have run high-resolution climate simulations of temperatures across the United States.

The researchers were specifically looking at the potential effects of a global 2 degree Celsius (3.6 degrees Fahrenheit) warming and found it leads to increasing extreme summer heat waves -- of a lot more than 2 degrees C -- all over the United States, and especially in the West.

Their concern is that limiting global warming to 2 degrees C, as was discussed at the 2009 Copenhagen climate meeting, may not be enough to avoid dangerous climate change.

"The upshot is that we don't live in the global mean. What seems like a small warming can mean a lot of change," in specific places, said Noah Diffenbaugh of Stanford University.

Diffenbaugh and Moetasim Ashfaq published their results in the latest issue of the journal Geophysical Research Letters.

A single degree of global mean rise in temperature can lead to 2 or 3 degrees rise in summer temperatures in North America, Diffenbaugh explained. And that gives a leg up to extreme heat events, which always spike much higher than any means or averages.

The simulation shows that in the second half of this century there will be an additional five to eight record-breaking heat waves per decade over much of the country. The worst heat will be in the Western United States, with up to nine record-breaking heat events per decade as a result of that global mean warming of 2 degrees C.

That's a miserable, deadly heat wave almost every year.

"It's the rare becoming normal," Diffenbaugh told Discovery News.

The researchers looked at the 2 degree C warming because it is a marker that has been batted around a lot by scientists and policy makers. It's also a rather deceptive number, because it's not about how much warming will happen between now and 2040, but how much warming happens from the time humans started large-scale fossil fuel burning in the 1800s until 2040.

The global mean temperature has already risen 0.8 degrees C since pre-industrial times, nearly halfway to a 2-degree-C mark, explained climate scientist Jerry Meehl of the National Center for Atmospheric Research in Colorado. As a result, the heat waves in Russia, the northeastern United States and Japan this summer can all be attributed to the global warming that has already happened, he said.

"We are already seeing that," Meehl said of extreme heat events.

On the other hand, he said there will also be winter cold spells, though they ought to get less frequent as the summer heat waves ramp up.

"Winter still happens," said Meehl.

Even record-setting cold will happen without canceling out the extreme heat that's in store.

"We've published a prediction of the next three decades and we'll find out if it's correct," said Diffenbaugh.


Texas Citizens for Science
Last updated: 2011 June 9