Tag Archive: climatology

Apr 06 2012

Melting Artic ice affects European climate

Earth has seen some highly unusual weather patterns over the past three years, and three new studies published this year point to Arctic sea loss as a potential important driver of some of these strange weather patterns. The record loss of sea ice the Arctic in recent years may be increasing winter cold surges and snowfall in Europe and North America, says a study by a research team led by Georgia Institute of Technology scientists Jiping Liu and Judith Curry. The paper, titled “Impact of declining Arctic sea ice on winter snowfall”, was published on Feb. 27, 2012 in the online early edition of the journal Proceedings of the National Academy of Sciences. “Our study demonstrates that the decrease in Arctic sea ice area is linked to changes in the winter Northern Hemisphere atmospheric circulation, said Judith Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech, in a press release. “The circulation changes result in more frequent episodes of atmospheric blocking patterns, which lead to increased cold surges and snow over large parts of the northern continents.”

Figure 1. Arctic sea ice in September 2007 reached its lowest extent on record, approximately 40% lower than when satellite records began in 1979. Sea ice loss in 2011 was virtually tied with the ice loss in 2007, despite weather conditions that were not as unusual in the Arctic. Image credit: University of Illinois Cryosphere Today.

Figure 2. The extent of Arctic sea ice loss in the summer July – August – September period in 2007 was about 1.4 million square miles (3.6 million square kilometers) greater than in 1980, according to the University of Illinois Cryosphere Today. For comparison, the lost ice coverage (orange colors) was equal to an area about 44% of the size of the contiguous U.S., or 71% of the non-Russian portion of Europe.

Summertime Arctic sea ice loss: 40% since 1980
The Arctic has seen a stunning amount of sea ice loss in recent years, due to melting and unfavorable winds that have pushed large amounts of ice out of the region. Forty percent of the sea ice was missing in September 2007, compared to September of 1980. This is an area equivalent to about 44% of the contiguous U.S., or 71% of the non-Russian portion of Europe. Such a large area of open water is bound to cause significant impacts on weather patterns, due to the huge amount of heat and moisture that escapes from the exposed ocean into the atmosphere over a multi-month period following the summer melt. The Georgia Tech study found that Arctic sea ice loss had caused a 20 – 60% weakening of the west-to-east belt of winds circling the pole in recent years, producing broader meanders in the jet stream that allowed it to get “stuck” in place 20 – 60% more often. When the jet stream gets stuck in place for a long period of time, we say a “blocking pattern” has set up. Since the jet stream marks the boundary between cold, Arctic air to the north, and warmer subtropical air to the south, areas on both sides of the jet are subjected to extended periods of unusually warm or cold weather during a blocking episode. Such a blocking pattern began on January 26, 2012 and lasted until February 11, bringing and exceptionally cold and snowy conditions to much of Europe, which lay on the cold side of an elongated loop of the jet stream that got stuck in place. Conversely, most of North America and northern Siberia saw unusually warm temperatures during this period, since they were on the warm side of the jet stream. Lead author Jiping Liu, a senior research scientist in the School of Earth and Atmospheric Sciences at Georgia Tech, added, “We think the recent snowy winters could be caused by the retreating Arctic ice altering atmospheric circulation patterns by weakening westerly winds, increasing the amplitude of the jet stream and increasing the amount of moisture in the atmosphere. These pattern changes enhance blocking patterns that favor more frequent movement of cold air masses to middle and lower latitudes, leading to increased heavy snowfall in Europe and the Northeast and Midwest regions of the United States.” The paper concludes: “if Arctic sea ice continues as anticipated by climate modeling results, we speculate that episodes of the aforementioned circulation change will become more frequent, along with more persistent snowstorms over northern continents during winter.”

Figure 3. Waiting for the warm-up after a rare snowfall in Italy during the February, 2012 European cold blast. Image credit: wunderphotographer cathykiro.

Two other studies link Arctic sea ice loss to atmospheric circulation changes
“The question is not whether sea ice loss is affecting the large-scale atmospheric circulation…it’s how can it not?” That was the take-home message from Dr. Jennifer Francis of Rutgers University, in her talk “Evidence Linking Arctic Amplification to Extreme Weather in Mid-latitudes, presented at December’s American Geophysical Union meeting in San Francisco. Dr. Francis presented new research that has just been published in the journal Geophysical Research Letters, which shows that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions. Dr. Francis describes her work in a March 5, 2012 post on the Yale environment360 web site.

“Even if the current weather situation may seem to speak against it, the probability of cold winters with much snow in Central Europe rises when the Arctic is covered by less sea ice in summer.” That was the opening sentence of a January 26, 2012 press release by a group of European scientists, led by Ralf Jaiser of the Alfred Wegener Institute in Germany. The words proved prescient, because that day marked the beginning of a brutal two-week cold air outbreak over Central and Eastern Europe that killed 823 people and did over $660 million in damage, according to preliminary estimates by insurance broker Aon Benfield. Dr. Jaiser’s team, using modeling studies, showed that Arctic sea ice loss weakens upper-level winds over the Arctic in winter, allowing an increased chance of cold air surges over Europe.


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Permanent link to this article: http://www.euaclan.org/2012/04/melting-artic-ice-affects-european-climate/

Mar 08 2012

Modeling Arctic Climate

What’s in a model?
Computer climate models are based on scientists’ understanding of Earth’s climate. The models use mathematical relationships to try to quantify the relationships between parts of the climate system. If you tweak one factor in climate, how does the simulated climate system respond? Models that bring many factors together help scientists learn how the climate system works, and let them run simulations on Earth’s climate. They also allow scientists to assess how climate may be affected by present and future changes in greenhouse gases and solar forcing, and how much of a role natural variability plays.

In climate, researchers know that at least one factor is changing—the amount of greenhouse gases in the atmosphere has increased by 40 percent since the Industrial Revolution. Basic physics tells us that increasing greenhouse gases will increase temperatures on average, but where, when, and how exactly the climate will change depends on a lot of other variables such as atmospheric conditions, ocean circulation, ice loss, and plant growth. NSIDC scientist Julienne Stroeve studies sea ice and climate. She said, “Climate models can tell us about how these components of our planet interact and influence each other, and to understand what happens when we perturb one of these components.”

To test their models and their current understanding of how climate works, climate scientists also run their models through past and current climate scenarios, to determine how well they can replicate the observed climate variability and trends. Stroeve said, “Because the real world provides just one realization of both natural variability and forced climate change, we cannot separate out natural climate change from say greenhouse gases in observational data.” Models, she said, allow researchers to run a test many times, and answer questions such as how much added greenhouse gases are changing climate, compared to natural variatiability.

Experimenting with the climate
Today’s global climate models are made up of many sub-models that replicate a specific system such as the atmosphere, the ocean, or land. They include factors like algae in the ocean and dust on sea ice, which can both be affected by climate and affect climate themselves. Adding in detailed factors like shrub growth make the models more complicated, but they also help scientists better understand climate. NCAR scientists David Lawrence said. “The best models can take this information and very accurately reproduce the Earth’s climate and weather, with major precipitation zones and circulation patterns and modes of variability such as the El Niño Southern Oscillation (ENSO) matching very reasonably with observations.”

For example, Lawrence has been researching how changing plant life in the Arctic could affect climate. On the Arctic tundra, the number of shrubs is increasing as the air and land get warmer.  But the shrubs themselves have additional effects on the climate. Lawrence said, “Shrubs are darker than the surrounding tundra so they tend to absorb more solar radiation, thereby warming the nearby air.” But at the same time,  shrubs tend to shade the ground below them, making the soil cooler. In a recently published study, Lawrence used a climate model to study how an expected increase in shrubs will alter permafrost vulnerability to climate change. He found that more shrubs are likely to increase permafrost vulnerability to climate change, in contrast to previous studies that suggested that shrubs would have the opposite effect.

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Permanent link to this article: http://www.euaclan.org/2012/03/modeling-arctic-climate/

Jan 12 2011

A ‘Bulge’ in Atmospheric Pressure Gives Us a Super-Cold Winter Amid Global Warming

Το παρακάτω άρθρο δημοσιεύτηκε στους NY Times. Πραγματεύεται το γεγονός οτι μάλλον το φαινόμενο του θερμοκηπίου επηρρεάζει τη ζωνική κυκλοφορία αλλάζοντας τις τυπικές μετεωρολογικές συνθήκες μιας περιοχής. Προφανώς η εφημερίδα είναι Αμερικάνικη και μιλά για τις ΗΠΑ, σε κάθε περίπτωση όμως είναι ένα σενάριο που δείχνει να επικρατεί και παγκόσμια. Δια εγκυκλοπαιδικήν γνώση λοιπόν…

Icicle-covered oranges in Florida. The United Kingdom swamped with its coldest December in more than a century. Travelers stranded in airports surrounded by snowy fortresses.

These have been some of the dominant images this winter, and now one forecaster says it’s going to get colder. Yesterday, an AccuWeather meteorologist predicted that January could be the chilliest for the nation as a whole since the 1980s.

“More waves of Arctic air will invade the country, starting late this week and continuing through the next week and beyond,” explained Joe Bastardi of Accuweather in a release. Rare snowfall is headed to Seattle, while the Texas citrus industry may have to prepare for cold-weather damage, according to his forecast.

So how does this fit with global warming models?

According to some climate scientists, the cold in places like Florida actually could be a sign of warming, rather than an argument against the phenomenon.

The ongoing disappearance of sea ice in the Arctic from elevated temperatures is a factor to changes in atmospheric pressure that control jet streams of air, explained James Overland, an oceanographer of the National Oceanic and Atmospheric Administration, or NOAA. That is because ice-less ocean is darker and, thus, absorbs more solar heat, which in turn spews warmer air than average back into the Arctic atmosphere.

That unusually warm air can contribute to a “bulge” effect to the atmospheric pressure controlling how cold air flows, according to Overland, who works at NOAA’s Pacific Marine Environmental Laboratory. Rather than moving circularly in the Arctic from west to east as typical, the bulge may prompt air to move in a U-shaped pattern down to the southern United States.

How loss of Arctic ice gives you snow in Seattle

Last year was the waviest example of this pressure phenomenon in 145 years, said Overland. What also is happening is that the wavy air flow from north to south is appearing for longer periods of time, rather than just for a week or two, he said.

“You can’t go as far as saying the loss of sea ice is causing cold weather in Florida,” said Overland. “You can say it is a contributing factor.” In October, Overland co-authored part of NOAA’s Arctic Report Card, which included a section on how Arctic weather is influencing weather in mid-latitudes.

He emphasized that more research needs to be done on the cause and effect relationship between disappearing Arctic sea ice and cold weather in southern locations. Other research backs up his argument.

In November, climate scientist Vladimir Petoukhov reported in the Journal of Geophysical Research that the overall warming of Earth’s northern half could result in cold winters. “These anomalies could triple the probability of cold winter extremes in Europe and northern Asia,” he said in a statement.

The area covered by sea ice hovered near its historic low this summer, and is expected to be largely gone by mid-century (ClimateWire, Dec. 17, 2010).

Another study published in Environmental Research Letters last year, though, predicted colder winters in the United Kingdom because of natural variations in solar activity.

Differing from the majority of scientists, meteorologist Bastardi presented his “global cooling” theory in a December AccuWeather video arguing that carbon dioxide is a trace gas that has less effect on weather than forces such as the sun.

“There’s no need to panic over global warming,” he said.

The key thing is to look at the climate over long periods of time and not try to find meaning in one weather event, said David Easterling, chief of the Scientific Services Division at NOAA’s National Climatic Data Center.

“The flip side is it’s been unusually warm in Canada this winter,” he said.

January aside, the National Weather Service predicts that swaths of the country stretching from the Southwest to the Southeast will be warmer than average this year. Record high temperatures are currently outnumbering record low temperatures by about two to one, and those ratios are projected to be about 20 to 1 by mid-century and 50 to 1 by 2100, said Jerry Meehl, a scientist at the National Center for Atmospheric Research.

How much the existing data registers with politicians and the public is an open question.

Sen. James Inhofe (R-Okla.), who once called global warming a “hoax” and was one of the loudest opponents against climate legislation last year, posted a blog last month mentioning recent cold weather events.

How weather impacts belief

“The fanciful claims surrounding global warming have turned out to be a colossal deception, an artful hoax, and an intellectual fraud,”

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Permanent link to this article: http://www.euaclan.org/2011/01/a-bulge-in-atmospheric-pressure-gives-us-a-super-cold-winter-amid-global-warming/

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