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."

View the original article here

Air pollution over Asia influences global weather and makes Pacific storms more intense

In the first study of its kind, scientists have compared air pollution rates from 1850 to 2000 and found that anthropogenic (human-made) particles from Asia impact the Pacific storm track that can influence weather over much of the world.

The team, which includes several researchers from Texas A&M University, has had its work published in the current issue of Proceedings of the National Academy of Sciences (PNAS).

Yuan Wang, Yun Lin, Jiaxi Hu, Bowen Pan, Misti Levy and Renyi Zhang of Texas A&M's Department of Atmospheric Sciences, along with colleagues from Pacific Northwest National Laboratory, the University of California at San Diego and NASA's Jet Propulsion Laboratory, contributed to the work.

The team used detailed pollution emission data compiled by the Intergovernmental Panel on Climate Change and looked at two scenarios: one for a rate in 1850 -- the pre-Industrial era -- and from 2000, termed present-day.

By comparing the results from an advanced global climate model, the team found that anthropogenic aerosols conclusively impact cloud formations and mid-latitude cyclones associated with the Pacific storm track.

"There appears to be little doubt that these particles from Asia affect storms sweeping across the Pacific and subsequently the weather patterns in North America and the rest of the world," Zhang says of the findings.

"The climate model is quite clear on this point. The aerosols formed by human activities from fast-growing Asian economies do impact storm formation and global air circulation downstream. They tend to make storms deeper and stronger and more intense, and these storms also have more precipitation in them. We believe this is the first time that a study has provided such a global perspective."

In recent years, researchers have learned that atmospheric aerosols affect the climate, either directly by scattering or absorbing solar radiation, and indirectly by altering cloud formations. Increasing levels of such particles have raised concerns because of their potential impacts on regional and global atmospheric circulation.

In addition, Zhang says large amounts of aerosols and their long-term transport from Asia across the Pacific can clearly be seen by satellite images.

The Pacific storm track represents a critical driver in the general global circulation by transporting heat and moisture, the team notes. The transfer of heat and moisture appears to be increased over the storm track downstream, meaning that the Pacific storm track is intensified because of the Asian air pollution outflow.

"Our results support previous findings that show that particles in the air over Asia tend to affect global weather patterns," Zhang adds.

"It shows they can affect the Earth's weather significantly."

Yuan Wang, who conducted the research with Zhang while at Texas A&M, currently works at NASA's Jet Propulsion Laboratory as a Caltech Postdoctoral Scholar.

The study was funded by grants from NASA, the Department of Energy, Texas A&M's Supercomputing facilities and the Ministry of Science and Technology of China.

View the original article here

Warm U.S. West, cold East: 4,000-year pattern; Global warming may bring more curvy jet streams during winter

These maps show winter temperature patterns (top) and winter precipitation patterns (bottom) associated with a curvy jet stream (not shown) that moves north from the Pacific to the Yukon and Alaska, then plunges down over the Canadian plains and into the eastern United States. A University of Utah-led study shows that starting 4,000 years ago, the jet stream tended to become curvier than it was between 8,000 and 4,000 years ago, and suggests global warming will enhance such curviness and thus frigid weather in the eastern states similar to this past winter's. The curvy jet stream brought abnormally warm temperatures (red and orange) to the West and Alaska and an abnormal deep freeze (blue) to the East this past winter, similar to what is shown in the top map, except the upper Midwest was colder than shown. The bottom map of a typical curvy jet stream precipitation pattern shows how that normally brings dry winters to reddish-orange areas and wet winters to blue regions. Precipitation patterns this winter matched the bottom map in many regions, except California was drier than expected and the upper Midwest was wetter than expected.Credit: Zhongfang Liu, Tianjin Normal University, China. Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, and suggests it may worsen as Earth's climate warms.

"If this trend continues, it could contribute to more extreme winter weather events in North America, as experienced this year with warm conditions in California and Alaska and intrusion of cold Arctic air across the eastern USA," says geochemist Gabe Bowen, senior author of the study.

The study was published online April 16 by the journal Nature Communications.

"A sinuous or curvy winter jet stream means unusual warmth in the West, drought conditions in part of the West, and abnormally cold winters in the East and Southeast," adds Bowen, an associate professor of geology and geophysics at the University of Utah. "We saw a good example of extreme wintertime climate that largely fit that pattern this past winter," although in the typical pattern California often is wetter.

It is not new for scientists to forecast that the current warming of Earth's climate due to carbon dioxide, methane and other "greenhouse" gases already has led to increased weather extremes and will continue to do so.

The new study shows the jet stream pattern that brings North American wintertime weather extremes is millennia old -- "a longstanding and persistent pattern of climate variability," Bowen says. Yet it also suggests global warming may enhance the pattern so there will be more frequent or more severe winter weather extremes or both.

"This is one more reason why we may have more winter extremes in North America, as well as something of a model for what those extremes may look like," Bowen says. Human-caused climate change is reducing equator-to-pole temperature differences; the atmosphere is warming more at the poles than at the equator. Based on what happened in past millennia, that could make a curvy jet stream even more frequent and-or intense than it is now, he says.

Bowen and his co-authors analyzed previously published data on oxygen isotope ratios in lake sediment cores and cave deposits from sites in the eastern and western United States and Canada. Those isotopes were deposited in ancient rainfall and incorporated into calcium carbonate. They reveal jet stream directions during the past 8,000 years, a geological time known as middle and late stages of the Holocene Epoch.

Next, the researchers did computer modeling or simulations of jet stream patterns -- both curvy and more direct west to east -- to show how changes in those patterns can explain changes in the isotope ratios left by rainfall in the old lake and cave deposits.

They found that the jet stream pattern -- known technically as the Pacific North American teleconnection -- shifted to a generally more "positive phase" -- meaning a curvy jet stream -- over a 500-year period starting about 4,000 years ago. In addition to this millennial-scale change in jet stream patterns, they also noted a cycle in which increases in the sun's intensity every 200 years make the jet stream flatter.

Bowen conducted the study with Zhongfang Liu of Tianjin Normal University in China, Kei Yoshimura of the University of Tokyo, Nikolaus Buenning of the University of Southern California, Camille Risi of the French National Center for Scientific Research, Jeffrey Welker of the University of Alaska at Anchorage, and Fasong Yuan of Cleveland State University.

The study was funded by the National Science Foundation, National Natural Science Foundation of China, Japan Society for the Promotion of Science and a joint program by the society and Japan's Ministry of Education, Culture, Sports, Science and Technology: the Program for Risk Information on Climate Change.

Sinuous Jet Stream Brings Winter Weather Extremes

The Pacific North American teleconnection, or PNA, "is a pattern of climate variability" with positive and negative phases, Bowen says.

"In periods of positive PNA, the jet stream is very sinuous. As it comes in from Hawaii and the Pacific, it tends to rocket up past British Columbia to the Yukon and Alaska, and then it plunges down over the Canadian plains and into the eastern United States. The main effect in terms of weather is that we tend to have cold winter weather throughout most of the eastern U.S. You have a freight car of arctic air that pushes down there."

Bowen says that when the jet stream is curvy, "the West tends to have mild, relatively warm winters, and Pacific storms tend to occur farther north. So in Northern California, the Pacific Northwest and parts of western interior, it tends to be relatively dry, but tends to be quite wet and unusually warm in northwest Canada and Alaska."

This past winter, there were times of a strongly curving jet stream, and times when the Pacific North American teleconnection was in its negative phase, which means "the jet stream is flat, mostly west-to-east oriented," and sometimes split, Bowen says. In years when the jet stream pattern is more flat than curvy, "we tend to have strong storms in Northern California and Oregon. That moisture makes it into the western interior. The eastern U.S. is not affected by arctic air, so it tends to have milder winter temperatures."

The jet stream pattern -- whether curvy or flat -- has its greatest effects in winter and less impact on summer weather, Bowen says. The curvy pattern is enhanced by another climate phenomenon, the El Nino-Southern Oscillation, which sends a pool of warm water eastward to the eastern Pacific and affects climate worldwide.

Traces of Ancient Rains Reveal Which Way the Wind Blew

Over the millennia, oxygen in ancient rain water was incorporated into calcium carbonate deposited in cave and lake sediments. The ratio of rare, heavy oxygen-18 to the common isotope oxygen-16 in the calcium carbonate tells geochemists whether clouds that carried the rain were moving generally north or south during a given time.

Previous research determined the dates and oxygen isotope ratios for sediments in the new study, allowing Bowen and colleagues to use the ratios to tell if the jet stream was curvy or flat at various times during the past 8,000 years.

Bowen says air flowing over the Pacific picks up water from the ocean. As a curvy jet stream carries clouds north toward Alaska, the air cools and some of the water falls out as rain, with greater proportions of heavier oxygen-18 falling, thus raising the oxygen-18-to-16 ratio in rain and certain sediments in western North America. Then the jet stream curves south over the middle of the continent, and the water vapor, already depleted in oxygen-18, falls in the East as rain with lower oxygen-18-to-16 ratios.

When the jet stream is flat and moving east-to-west, oxygen-18 in rain is still elevated in the West and depleted in the East, but the difference is much less than when the jet stream is curvy.

By examining oxygen isotope ratios in lake and cave sediments in the West and East, Bowen and colleagues showed that a flatter jet stream pattern prevailed from about 8,000 to 4,000 years ago in North America, but then, over only 500 years, the pattern shifted so that curvy jet streams became more frequent or severe or both. The method can't distinguish frequency from severity.

The new study is based mainly on isotope ratios at Buckeye Creek Cave, W. Va.; Lake Grinell, N.J.; Oregon Caves National Monument; and Lake Jellybean, Yukon.

Additional data supporting increasing curviness of the jet stream over recent millennia came from seven other sites: Crawford Lake, Ontario; Castor Lake, Wash.; Little Salt Spring, Fla.; Estancia Lake, N.M.; Crevice Lake, Mont.; and Dog and Felker lakes, British Columbia. Some sites provided oxygen isotope data; others showed changes in weather patterns based on tree ring growth or spring deposits.

Simulating the Jet Stream

As a test of what the cave and lake sediments revealed, Bowen's team did computer simulations of climate using software that takes isotopes into account.

Simulations of climate and oxygen isotope changes in the Middle Holocene and today resemble, respectively, today's flat and curvy jet stream patterns, supporting the switch toward increasing jet stream sinuosity 4,000 years ago.

Why did the trend start then?

"It was a when seasonality becomes weaker," Bowen says. The Northern Hemisphere was closer to the sun during the summer 8,000 years ago than it was 4,000 years ago or is now due to a 20,000-year cycle in Earth's orbit. He envisions a tipping point 4,000 years ago when weakening summer sunlight reduced the equator-to-pole temperature difference and, along with an intensifying El Nino climate pattern, pushed the jet stream toward greater curviness.

View the original article here

European climate at the 2 degrees Celsius global warming threshold

A global warming of 2??C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change.

However, a new study shows that, even at this threshold, substantial and robust changes may be expected across Europe. Most of Europe will warm more than the global average with increases over +3 degrees over Northern Europe in winter and Central-Southern Europe in summer.

Similar increases are also shown for extremes of temperature. Precipitation patterns at +2C global warming show the now familiar wet-north and dry-south patterns and increasing heavy precipitation across much of Europe in both winter and summer.

These conclusions appear in a new study published in Environmental Research Letters in March and recently highlighted in Nature. Stefan Sobolowski at Uni Research and the Bjerknes Centre is co-author in the study led by Robert Vautard at the Pierre-Simon Laplace Institute in Gif-sur-Yvette, France.

This research was performed as part of an EU-FP7 project called IMPACT2C, which investigates the potential impacts in Europe and abroad even if society manages to keep globally averaged warming to around 2 degrees celsius. Crossing the +2 degree threshold is essentially a mid-century or earlier event under both the older IPCC scenarios and the new representative concentration pathways (RCPs).

Weather and climate is experienced locally The only way it is avoided is under the very aggressive, and increasingly unlikely, RCP2.6 scenario. The patterns of change, with the exception of regional variations, are now well known. What is new in this study is the fact that it can be shown that even at the global threshold of +2C substantial regional to local scale changes occur.

A global warming of +2C is somewhat abstract concept to many people. We do not experience weather and climate globally, we experience it locally. And this study places these changes in a spatial context that is relevant for the public.

Further, this study shows that these changes not as far away as we might think; a few decades at most.

"To put this in perspective," Dr. Sobolowski says, "this will be about the time that my daughter reaches adulthood."

Story Source:

The above story is based on materials provided by Uni Research. Note: Materials may be edited for content and length.

View the original article here

Toyota, Honda global output halved after quake (AFP)

TOKYO (AFP) – Japanese auto giants Toyota and Honda saw global production halved in April as the March 11 earthquake and tsunami ravaged supply chains, the companies said Friday.

Honda reported a 52.9 percent year-on-year drop in worldwide production and an 81.0 percent slump in domestic output, while Toyota said global production was down 48.1 percent.

The quake and the resulting tsunami shattered component supply chains and crippled electricity-generating facilities, including a nuclear power plant at the centre of an ongoing atomic emergency.

Amid power and parts shortages, Toyota had announced production disruptions domestically and in the United States, Europe, China and Australia because of the crisis, temporarily slowing output or shutting plants.

The company announced a year-on-year drop of 15.4 percent in its global sales figures for April.

Honda, which was forced to temporarily suspend all production at its Japanese sites, said domestic sales were down 46.3 percent on year while exports dropped 76.2 percent.

"The figures are pretty much along the lines of what we had expected. The months of March and April are the most severely hit by the disaster," Ryoichi Saito, an auto analyst at Mizuho Investors Securities, said.

"In April, we saw auto plants operating for only about half the month, about half the capacity."

Many component manufacturers that are key to auto production are based in the worst-hit regions of Japan, their facilities damaged by the 9.0 magnitude earthquake or inundated by the giant wave that followed.

While most plants resumed production by mid-April, operations remain well below capacity and analysts warn parts shortages could go on for months, with the threat of summer power shortages also casting a shadow.

Honda said it expected production volume in Asia and Oceania to start picking up in July, the carmaker's Asian Honda Motor Co. unit said.

The company said in a statement it expects its production in Asia and Oceania "will be normalised during the August to September time period at almost all auto plants in the region", Dow Jones Newswires reported.

The picture looked less gloomy for Nissan Motor Co., however, which makes up Japan's big three automakers alongside Toyota and Honda.

The company said global production in April had decreased 22.4 percent on-year but announced a 4.4 percent rise in worldwide sales, marking an all-time record for the month of April.

"Production is picking up earlier than expected, and I expect auto production will recover considerably in June," Saito told AFP. "Auto part makers for Toyota have also said their production will come to about 90 percent of what it should be by June. I'd say production bottomed out in April and will start recovering in May."

Nissan plans to manufacture around 98,000 vehicles in Japan next month, the Nikkei daily said, nearly unchanged from the year-earlier 100,000 or so. And its projected June-November output of roughly 560,000 units is only slightly lower than the 590,000 units of a year earlier.

Total domestic auto output in fiscal 2011 is on course to reach around eight million units, the report said, just 10 percent off the figure for 2010.

The woes of Japan's automakers have been in stark contrast to overseas rivals. South Korea's Hyundai last month posted a 47 percent rise in first quarter net profit on higher prices and strong demand.

View the original article here