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shifting global and
local weather patterns

a briefing document

New translation, the Magna Carta

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shifting global and local weather patternsis one of a series in a series of briefing documents investigating the indicators, science, analysis and argument surrounding global warming.
One of a grouping of documents on global concerns at abelard.org.
on energy on global warming
sustainable futures briefing documents

On housing and making living systems ecological

Tectonics: tectonic plates - floating on the surface of a cauldron

click to see all the indexIndex
tropics altering position much faster than predicted
water pressure in the western usa, and shrinking glaciers
and in iceland
and in china
growing melting in greenland
grace satellite and ice
varying weather systems
north atlantic ocillation
changes in the northern hemisphere, 2010
el niño and la niña

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tropics altering position much faster than predicted

“Earth's tropical belt is expanding much faster than expected, and that could bring more storms to the temperate zone and drier weather to parts of the world that are already dry, climate scientists reported on Sunday.

“Remarkably, the tropics appear to have already expanded -- during only the last few decades of the 20th century -- by at least the same margin as models predict for this century," the scientists said in the current edition of Nature Geoscience.”

“Tropical temperatures are warm, and it rains a lot, with little seasonal or day-to-day change. The subtropics, by contrast, are generally dry. If the warm, wet tropical climate is spreading poleward, the dry subtropic climate may head for the poles too.

“Those dry subtropical bands could include some of the most heavily populated places on Earth, the scientists said: the Mediterranean, the US Southwest, northern Mexico, southern Australia, southern Africa and parts of South America.”

“Those storm tracks are linked with the position of the jet stream, which is one way we use to delineate the width of the tropics," Seidel said by telephone from NOAA's Air Resources Laboratory outside Washington. "The jet streams are moving poleward, and so, presumably, would the storm tracks.”

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And from the recent past:

“A thought came to me, when I was reading in the papers about the scandals of the regional government: scientists say the palm tree line, that is the climate favorable to the palm tree form of vegetation, is creeping northward at the rate, I think, of five hundred meters every year . It's rising like mercury in a thermometer.”

Sciascia, 1961.

water pressure in the western usa, and shrinking glaciers

“One of the United States' most beautiful landmarks may soon have to change its name. Glacier National Park in Montana, which once boasted 150 of the spectacular rivers of ice, is now down to 25, and the most recent data show that the remainder "may be gone in our lifetimes," an ecologist said here yesterday at a meeting of the American Geophysical Union. Other than the aesthetic loss, the disappearance of glaciers across the American West could cause huge problems for a regional population that is 85% dependent on mountain water and already coping with shortages.”

“ [...] The latest surveys conducted by the organization show that the glaciers are, on average, 1.7 meters thinner each year--a decline much more rapid than expected [...] ”

“ [...] Also contributing is carbon black, known more commonly as soot, which continually rains down on the glaciers but tends to concentrate on the surface of the ice. By the calculations of his research team, Painter said, soot increases heat absorption from the sun's rays by 43%. That provides "yet another reason" to limit carbon black from industrial emissions, [...] ” [Quoted from sciencenow.sciencemag.org]

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“Since 1950, the Sierra snowpack has decreased by about 20 percent, the temperature in the Rocky Mountains has gone up 3 degrees and spring water flow in the Columbia River has decreased significantly.

“ "These signals are the same no matter where you go in the West," marine physicist Tim Barnett of Scripps Institution of Oceanography said Tuesday at the annual meeting of the American Geophysical Union in San Francisco. "We've got a real serious problem."

“By scaling down global climate models to bring greater detail of the region, a team of scientists led by Barnett and atmospheric scientist Ben Santer of Lawrence Livermore National Laboratory projected these trends into the future and found a grim picture for the West. By about 2040, the Colorado Rockies will be nearly barren of snow as early as April 1 each year. And a similar story will play out in the Sierra.” [Quoted from mercurynews.com]

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“ "About 50 percent of the fresh water consumed by people worldwide comes from mountains, so the rate at which snowpack is disappearing is worrying, said Daniel Fagre, an ecologist who works for the US Geological Survey in Glacier National Park in Montana.

“Fagre said only about 25 of 150 glaciers that once dotted Glacier National Park remain. Initial data projected that, for the first time in more than 1,000 years, the park would be without ice floes by 2030, but more recent estimates project the icebergs may be lost even before then, Fagre said.

“ "The glaciers of Glacier National Park will be gone in our lifetimes," Fagre said, [...] ” [Quoted from planetark.org]

and in iceland:

“ "It's nice to have plants around, but well, it's not good. It gets better in Iceland, but the rest of the world sees the bad part," she says.

“Once the measuring tape is rolled up, Jonsson heads back to his truck. He checks a clipboard to figure out exactly how far the glacier has retreated: 41 meters, the largest retreat he has ever seen. That's almost half the length of a football field in a single year.

This isn't happy news for Solveig Thorvaldsdottir.

“ "I mean, what are we going to call our country when the ice all melts? We might as well call it lava land," she says.” [Quoted from npr.org]

and in china:

“High altitude glaciers in China's remote west have shrunk by up to 18 percent over the last five years due to global warming, state media said on Friday, citing preliminary results from an on-going survey.”

"Global warming has led to an increase in the average temperature in the western area of China over the past few decades. This has caused the glacial shrinking, a thawing of frozen earth and worsening arid conditions,[...] ” [Quoted from planetark.org]

Reference glaciers, for more detailed information.

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growing melting in greenland

“Scientist Ian Joughin says that in the past few years, Jakobshavn's speed has doubled.

“ "That's putting about twice as much ice into the fjord as a decade ago ... and twice as much into the ocean," he says.”

“The station has to be re-anchored into the ice because Greenland's entire ice sheet is moving. Joughin, from the University of Washington, pulls out his GPS unit and finds that the region has slid more than 100 yards closer to the ocean during the past year.

“He also measures a length of fishing line he had sunk straight down into the ice the previous summer to see how much of the ice has melted away. A lot of the line he had buried is lying on the surface.

“ "Wow," he says. "It's a meter and a half of melt since last year. … Almost five feet."

“Greenland's ice sheet deforms constantly, like pancake batter flowing on a griddle. Each year, more snow piles up in the middle, and each year, more ice slides off into the sea or melts away. At the moment, Greenland's melt water increases global sea level by about a quarter of an inch per decade. If that melt increases as the world warms, a melting Greenland will eventually eat away the shorelines of the world.”

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grace satellite and ice

“These new data come from the NASA/German Aerospace Center's Gravity Recovery and Climate Experiment (Grace). Launched in March 2002, the twin Grace satellites circle the globe using gravity to map changes in Earth's mass 500 kilometers (310 miles) below. They are providing a unique way to monitor and understand Earth's great ice sheets and glaciers. [“The continent of Antarctica has been losing more than 100 cubic kilometers (24 cubic miles) of ice per year since 2002.” Quoted from nasa.gov]

“Grace measurements have revealed that in just four years, from 2002 to 2006, Greenland lost between 150 and 250 cubic kilometers (36 to 60 cubic miles) of ice per year. One cubic kilometer is equal to about 264 billion gallons of water. That's enough melting ice to account for an increase in global sea level of as much as 0.5 millimeters (0.019 inches) per year, according to Isabella Velicogna and John Wahr of the University of Colorado, Boulder. They published their results in the scientific journal Nature last fall. Since global sea level has risen an average of three millimeters (0.1 inch) per year since 1993, Greenland's rapidly increasing contribution can't be overlooked.”

varying weather systems

There are various recognised local weather systems which occillate over fairly regular cycles. These are sometimes loosely referred to as interdecadally varying systems.

north atlantic oscillation

Winter NAO index. Image: Tim Osbourn, cru.uea.ac.uk
Winter North Atlantic Ocillation index. Image: Tim Osbourn, cru.uea.ac.uk

“The North Atlantic Oscillation (NAO) is one of the major modes of variability of the Northern Hemisphere atmosphere. It is particularly important in winter, when it exerts a strong control on the climate of the Northern Hemisphere. It is also the season that exhibits the strongest interdecadal variability.”

The chart above shows the differences between the normalised sea level pressure over Gibraltar and the normalised sea level pressure over Southwest Iceland. That is, it is the Gibraltar minus Iceland version of the NAO index. It is a useful index of NAO strength during winter (December to March). The black line is the trend.

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changes in the northern hemisphere, 2010

North Atlantic jet stream, 3 December 2010. North Atlantic jet stream, 4 December 2010.
North Atlantic jet stream, 3 December 2010. Image: meteociel.fr North Atlantic jet stream, 4 December 2010. Image: meteociel.fr  
Compare the above images with those for North America (animated)  

Jet stream over the USA, June 2010. Image: accuweather.com

Notice that the jet stream, which commonly goes across Britain and the Netherlands, has now been forced southward and is even showing breaks. The jet stream tends to push the atmosphere around, and northern winters are currently unusually cold. Meanwhile, the Arctic regions are warming more quickly than most of the planet. If the general (average) temperature of the planet rises, this means that the energy in the weather system is higher and, therefore, is liable to greater instabilities.

You can watch this effect as you steadily boil a saucepan of water; as the (average) temperature rises, so the water will show increasing agitation. You cannot predict the rapid changes in the roiling water, but you can measure an average temperature and observe the effect of the increasing energy. Do not confuse planetary warming with local weather systems.

El Niño and La Niña

These two current/wind systems are local factors in affecting weather.

El Niño is a temporary change in the equatorial Pacific Ocean’s climate, off Peru and Ecuador, during winter months. Usually, the east-to-west surface wind blows the ocean, warmed by the sun, so that water heaps up in the western Pacific. At the same time, cold water deep in the ocean is drawn eastwards, then wells up to replace the westward travelling warm water, so creating excellent fishing grounds. Thus, the normal situation is warm water (about 30°C) in the west, and cooler water (about 22°C) in the east.

During an El Niño period, the east-to-west winds become weaker, so less warm water is blown west and less colder water is drawn eastwards. This results in the eastern Pacific water being warmer, a characteristic of El Niño. Further, the warmer eastern ocean has the effect of weakening the westbound winds, which compounds this effect in a weak positive feedback loop.

The usual upwelling of cold, nutrient-rich water near South American coasts does not occur. The resulting warmer water temperature is associated with widespread weather perturbations in the area. This includes disturbing the route of the Pacific Jet Stream, and the death of fish and plankton.

Strong El Niños last about a year, resulting in wet winters in southwest Americas and droughts in Australia and Indonesia. El Niños occur roughly even three to seven years, but there is no set periodicity or strength.

La Niña is the cool current counterpart to El Niño, when a significant cooling of ocean currents occur. It occurs less frequently than El Niño.There is cooler water in the west and warmer water in the eastern Pacific. In this case, there will be unusually wet weather in Australasia and drought in the western equatorial Americas.

The names El Niño and La Niña come from the Spanish, meaning boy child and girl child. El Niño was so named because warm ocean currents would appear off Peru around Christmas time when ‘El Niño’, Jesus, was born.

related material

the melting of glaciers
global warming
Arctic melting ice, sea levels click to return to the index

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sustainable futures briefing documents

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