Tag Archives: Jet stream

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Arctic warming gives US and Europe the chills

The effects of Arctic climate change on the jet stream could mean harsher winters for some of the most highly populated regions of the world.

LONDON, 2 November, 2016 Warming in the Arctic – one of the fastest-warming regions on the planet – could be heightening the chances of extreme winters in Europe and the US.

As the Arctic warms, the stratospheric jet stream that brings occasionally catastrophic ice storms and record snow falls to the eastern United States could also be on the move, according to new research in the journal Nature Climate Change.

The phenomenon is a natural one. Some years the track of the jet stream is wavy, and delivers severe cold weather to the mid-latitudes of the northern hemisphere. Some years the pattern alters, and Europe in particular experiences mild winters. The temperate zones have always experienced occasional extremes. But climate change could be tilting the balance.

Extreme spells

“We’ve always had years with wavy and not so wavy jet-stream winds, but in the last one or two decades the warming Arctic could well have been amplifying the effects of the wavy patterns.

“This may have contributed to some recent extreme cold winter spells along the eastern seaboard of the United States, in western Asia and at times over the UK,” says Edward Hanna, a geographer at the University of Sheffield, UK, and one of a team of British, European and US scientists behind the study.

“Improving our ability to predict how climate change
is affecting the jet stream will help improve
our long-term prediction of winter weather”

The study doesn’t claim to settle the question: notoriously, climate is what you expect but weather is what you get, and it may be impossible to prove that this or that unexpected event happened because the global average temperatures are now at least 1°C higher than they used to be, before the human combustion of fossil fuels began to increase the concentration of the greenhouse gas carbon dioxide in the atmosphere from 280 parts per million to 400 ppm.

But there are changes in the Arctic that are happening because of global warming, and meteorologists have been watching the knock-on effect on the stratospheric winds, especially the jet stream.

In the same issue of the journal one group identified a persistent shift and a weakening in the Arctic winter polar vortex, a meteorological monster that plays a role in temperate zone weather patterns.

Others identified a link between Arctic changes and the speed of the jet stream, and its effect on transatlantic airline timetables.

Yet others have linked Arctic warming to dangerous extremes of heat further south, and yet another group has linked polar climate change to both ice storms and heatwaves.

Arctic signals

The debate continues. The important thing is to monitor the melting sea ice, the rising sea-surface temperatures and the emerging pattern of severe winter weather. If meteorologists can learn to read the signals from the Arctic, then communities could plan more effectively for the consequences.

“Improving our ability to predict how climate change is affecting the jet stream will help improve our long-term prediction of winter weather in some of the most highly populated regions of the world,” Professor Hanna says. “This would be highly beneficial for communities, businesses and entire economies in the northern hemisphere.

“The public could better prepare for severe winter weather and have access to extra crucial information that could help make life-saving and cost-saving decisions.” Climate News Network

The effects of Arctic climate change on the jet stream could mean harsher winters for some of the most highly populated regions of the world.

LONDON, 2 November, 2016 Warming in the Arctic – one of the fastest-warming regions on the planet – could be heightening the chances of extreme winters in Europe and the US.

As the Arctic warms, the stratospheric jet stream that brings occasionally catastrophic ice storms and record snow falls to the eastern United States could also be on the move, according to new research in the journal Nature Climate Change.

The phenomenon is a natural one. Some years the track of the jet stream is wavy, and delivers severe cold weather to the mid-latitudes of the northern hemisphere. Some years the pattern alters, and Europe in particular experiences mild winters. The temperate zones have always experienced occasional extremes. But climate change could be tilting the balance.

Extreme spells

“We’ve always had years with wavy and not so wavy jet-stream winds, but in the last one or two decades the warming Arctic could well have been amplifying the effects of the wavy patterns.

“This may have contributed to some recent extreme cold winter spells along the eastern seaboard of the United States, in western Asia and at times over the UK,” says Edward Hanna, a geographer at the University of Sheffield, UK, and one of a team of British, European and US scientists behind the study.

“Improving our ability to predict how climate change
is affecting the jet stream will help improve
our long-term prediction of winter weather”

The study doesn’t claim to settle the question: notoriously, climate is what you expect but weather is what you get, and it may be impossible to prove that this or that unexpected event happened because the global average temperatures are now at least 1°C higher than they used to be, before the human combustion of fossil fuels began to increase the concentration of the greenhouse gas carbon dioxide in the atmosphere from 280 parts per million to 400 ppm.

But there are changes in the Arctic that are happening because of global warming, and meteorologists have been watching the knock-on effect on the stratospheric winds, especially the jet stream.

In the same issue of the journal one group identified a persistent shift and a weakening in the Arctic winter polar vortex, a meteorological monster that plays a role in temperate zone weather patterns.

Others identified a link between Arctic changes and the speed of the jet stream, and its effect on transatlantic airline timetables.

Yet others have linked Arctic warming to dangerous extremes of heat further south, and yet another group has linked polar climate change to both ice storms and heatwaves.

Arctic signals

The debate continues. The important thing is to monitor the melting sea ice, the rising sea-surface temperatures and the emerging pattern of severe winter weather. If meteorologists can learn to read the signals from the Arctic, then communities could plan more effectively for the consequences.

“Improving our ability to predict how climate change is affecting the jet stream will help improve our long-term prediction of winter weather in some of the most highly populated regions of the world,” Professor Hanna says. “This would be highly beneficial for communities, businesses and entire economies in the northern hemisphere.

“The public could better prepare for severe winter weather and have access to extra crucial information that could help make life-saving and cost-saving decisions.” Climate News Network

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Evidence 'suggests climate change is worsening UK winter'

FOR IMMEDIATE RELEASE
Scientists at the UK Met Office say all the evidence supports the theory that the exceptionally wet and stormy winter affecting much of Britain is caused at least in part by climate change.

LONDON, 9 February – The British Government’s main climate science adviser, the UK Met Office, says the present exceptionally wet and stormy winter “could be a manifestation of climate change.”

Its chief scientist, Dame Julia Slingo, says the variable UK climate means there is “no definitive answer” to what is producing this winter weather, with the “most exceptional period of rainfall in 248 years”. But “all the evidence suggests there is a link to climate change”.

She said there was no evidence to counter what the basic science says will happen as the world warms – that heavy, fierce downpours of rain will occur more often.

“Nobody has come forward to counter the basic premise that if you have a warmer world you are going to get more intense heavy rain rates”

Dame Julia told BBC Radio: “We know that warmer air holds more water…As scientists we always go back to the evidence base. I always challenge the climate sceptics to provide me with the same level of scientific integrity of the evidence base. I can’t see it.

“Nobody has come forward to counter the basic premise that if you have a warmer world you are going to get more intense heavy rain rates…as we’re beginning to detect now over the UK.”

The Met Office, with the UK’s Centre for Ecology & Hydrology (CEH), has published a report, The recent storms and floods in the UK, which strikes a cautious note.

It concludes: “It is not possible, yet, to give a definitive answer on whether climate change has been a contributor or not” to the frequent and torrential rain, storms and floods affecting much of the UK since early December.

But deep in the detail of the report’s findings are clear statements by its authors showing they are convinced that climate change may be partly responsible, despite the well-known fickle nature of the British weather.

The report says, for example, that although the number of strong winter storms over the mid-latitude North Atlantic – the path of the current storms – has not increased since 1871, the storms’ average intensity has grown significantly. The continual run of deep depressions through December, January and into February is also unusual.

“What in the 1960s and 1970s might have been a 1 in 125 day event is now more likely to be a 1 in 85 day event”

There are questions as well about whether the jet stream “is making greater excursions north and south, and whether these waves in the jet stream are becoming more locked in one position.

“This is a critical question because it raises the possibility that disruption of our usual weather patterns may be how climate change may manifest itself.”

The report says there is now some emerging evidence that, over the United Kingdom, daily heavy rain events may be more frequent: “What in the 1960s and 1970s might have been a 1 in 125 day event is now more likely to be a 1 in 85 day event.”

It says there is an increasing body of evidence that shows that extreme daily rainfall rates are becoming more intense, and that the rate of increase is consistent with what is expected from fundamental physics. – Climate News Network

FOR IMMEDIATE RELEASE
Scientists at the UK Met Office say all the evidence supports the theory that the exceptionally wet and stormy winter affecting much of Britain is caused at least in part by climate change.

LONDON, 9 February – The British Government’s main climate science adviser, the UK Met Office, says the present exceptionally wet and stormy winter “could be a manifestation of climate change.”

Its chief scientist, Dame Julia Slingo, says the variable UK climate means there is “no definitive answer” to what is producing this winter weather, with the “most exceptional period of rainfall in 248 years”. But “all the evidence suggests there is a link to climate change”.

She said there was no evidence to counter what the basic science says will happen as the world warms – that heavy, fierce downpours of rain will occur more often.

“Nobody has come forward to counter the basic premise that if you have a warmer world you are going to get more intense heavy rain rates”

Dame Julia told BBC Radio: “We know that warmer air holds more water…As scientists we always go back to the evidence base. I always challenge the climate sceptics to provide me with the same level of scientific integrity of the evidence base. I can’t see it.

“Nobody has come forward to counter the basic premise that if you have a warmer world you are going to get more intense heavy rain rates…as we’re beginning to detect now over the UK.”

The Met Office, with the UK’s Centre for Ecology & Hydrology (CEH), has published a report, The recent storms and floods in the UK, which strikes a cautious note.

It concludes: “It is not possible, yet, to give a definitive answer on whether climate change has been a contributor or not” to the frequent and torrential rain, storms and floods affecting much of the UK since early December.

But deep in the detail of the report’s findings are clear statements by its authors showing they are convinced that climate change may be partly responsible, despite the well-known fickle nature of the British weather.

The report says, for example, that although the number of strong winter storms over the mid-latitude North Atlantic – the path of the current storms – has not increased since 1871, the storms’ average intensity has grown significantly. The continual run of deep depressions through December, January and into February is also unusual.

“What in the 1960s and 1970s might have been a 1 in 125 day event is now more likely to be a 1 in 85 day event”

There are questions as well about whether the jet stream “is making greater excursions north and south, and whether these waves in the jet stream are becoming more locked in one position.

“This is a critical question because it raises the possibility that disruption of our usual weather patterns may be how climate change may manifest itself.”

The report says there is now some emerging evidence that, over the United Kingdom, daily heavy rain events may be more frequent: “What in the 1960s and 1970s might have been a 1 in 125 day event is now more likely to be a 1 in 85 day event.”

It says there is an increasing body of evidence that shows that extreme daily rainfall rates are becoming more intense, and that the rate of increase is consistent with what is expected from fundamental physics. – Climate News Network

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Greenland’s great melt is pinned on climate change

FOR IMMEDIATE RELEASE The forensic search for the mysterious agent that almost melted Greenland goes on. The latest suspect to be rounded up for questioning is the jet stream, according to scientists in Sheffield, in the UK. LONDON, 18, June – First: the story so far. For a few days in July 2012, almost 97% of the surface of Greenland began suddenly to thaw. This was a melt on an unprecedented scale. Greenland carries a burden of three million cubic kilometres of ice and even in the summer, most of it stays frozen, partly because of the island’s high latitude and partly because ice reflects sunlight, and tends normally to serve as its own insulator. The event was so unusual, and so unexpected, and on such a scale that nobody seriously suggested that the dramatic conversion of snow to slush was direct evidence of climate change because of human-induced global warming. Soot, smoke and heat At first, climatologists were inclined to see the thaw as a consequence of the record-breaking heat waves and forest fires that afflicted North America last summer: snow could have been darkened by columns of soot and smoke from forest fires, just enough to start absorbing the sunlight, some reasoned. Then in April a team at the University of Wisconsin-Madison suggested that freak cloud behaviour over Greenland at the time might have caused the melting. Clouds normally block sunlight and keep the terrain below them cool. But these clouds could have been thin enough to let solar radiation through, but thick enough to trap the consequential infra-red radiation from the ground, and raise the local temperature levels. Now Edward Hanna and colleagues at Sheffield report in the International Journal of Climatology that they have another explanation. Unusual atmospheric circulation and changes in the jet stream – the same changes that almost washed away summer in England – sent a blister of warm air sweeping over the ice sheet. Hanna and his team analysed all the weather data collected by the Danish Meteorological Institute and by US researchers, and then employed satellite readings and a computer simulation called SnowModel to reconstruct the strange turn of events. And climate change may after all be a suspect.   High melt years The Greenland Ice Sheet is a highly sensitive indicator of regional and global change, and, says Prof Hanna, been undergoing rapid warming, and losing ice, for at least the last five years and probably the last 20. “Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting.” This was not predicted by the climate models used by the Intergovernmental Panel on Climate Change, and perhaps that indicated a deficiency in those models, he suggested. The event seemed to be linked to changes in a phenomenon known to oceanographers and meteorologists as the summer North Atlantic Oscillation (NAO), another well-observed high pressure system called the Greenland Blocking Index, and the polar jet stream, all of which sent warm southerly winds sweeping over Greenland’s western coast. “The next five to 10 years will reveal whether or not 2012 was a rare event resulting from natural variability of the NAO or part of an emerging pattern of new extreme high melt years.” It was hard to predict future changes in the Greenland climate in the current state of knowledge, but important to keep on trying. There is an awful lot of ice on top of Greenland. Once it starts to melt, it is likely to be, say the Sheffield scientists,  “dominant contributor to global sea level change over the next 100 to 1,000 years.”- Climate News Network

FOR IMMEDIATE RELEASE The forensic search for the mysterious agent that almost melted Greenland goes on. The latest suspect to be rounded up for questioning is the jet stream, according to scientists in Sheffield, in the UK. LONDON, 18, June – First: the story so far. For a few days in July 2012, almost 97% of the surface of Greenland began suddenly to thaw. This was a melt on an unprecedented scale. Greenland carries a burden of three million cubic kilometres of ice and even in the summer, most of it stays frozen, partly because of the island’s high latitude and partly because ice reflects sunlight, and tends normally to serve as its own insulator. The event was so unusual, and so unexpected, and on such a scale that nobody seriously suggested that the dramatic conversion of snow to slush was direct evidence of climate change because of human-induced global warming. Soot, smoke and heat At first, climatologists were inclined to see the thaw as a consequence of the record-breaking heat waves and forest fires that afflicted North America last summer: snow could have been darkened by columns of soot and smoke from forest fires, just enough to start absorbing the sunlight, some reasoned. Then in April a team at the University of Wisconsin-Madison suggested that freak cloud behaviour over Greenland at the time might have caused the melting. Clouds normally block sunlight and keep the terrain below them cool. But these clouds could have been thin enough to let solar radiation through, but thick enough to trap the consequential infra-red radiation from the ground, and raise the local temperature levels. Now Edward Hanna and colleagues at Sheffield report in the International Journal of Climatology that they have another explanation. Unusual atmospheric circulation and changes in the jet stream – the same changes that almost washed away summer in England – sent a blister of warm air sweeping over the ice sheet. Hanna and his team analysed all the weather data collected by the Danish Meteorological Institute and by US researchers, and then employed satellite readings and a computer simulation called SnowModel to reconstruct the strange turn of events. And climate change may after all be a suspect.   High melt years The Greenland Ice Sheet is a highly sensitive indicator of regional and global change, and, says Prof Hanna, been undergoing rapid warming, and losing ice, for at least the last five years and probably the last 20. “Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting.” This was not predicted by the climate models used by the Intergovernmental Panel on Climate Change, and perhaps that indicated a deficiency in those models, he suggested. The event seemed to be linked to changes in a phenomenon known to oceanographers and meteorologists as the summer North Atlantic Oscillation (NAO), another well-observed high pressure system called the Greenland Blocking Index, and the polar jet stream, all of which sent warm southerly winds sweeping over Greenland’s western coast. “The next five to 10 years will reveal whether or not 2012 was a rare event resulting from natural variability of the NAO or part of an emerging pattern of new extreme high melt years.” It was hard to predict future changes in the Greenland climate in the current state of knowledge, but important to keep on trying. There is an awful lot of ice on top of Greenland. Once it starts to melt, it is likely to be, say the Sheffield scientists,  “dominant contributor to global sea level change over the next 100 to 1,000 years.”- Climate News Network

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Climate change 'causes wild weather'

EMBARGOED until 2000 GMT on Monday 25 February
Extreme weather is often the result of climate change, according to scientists in Germany, who say they have found how greenhouse gases are helping to trap the jet stream and the weather patterns it brings.

LONDON, 25 February – The cause of much of the recent extreme weather across the world is climate change triggered by human activities, scientists say.

The Earth has experienced a range of severe regional weather extremes in recent years, including the heat waves of 2011 in the US and 2010 in Russia, a year that also brought the unprecedented Pakistan floods.

Behind these distinct events, though, there is a common physical cause, according to a team at the Potsdam Institute for Climate Impact Research (PIK), Germany.

Their paper, which helps to explain the mechanism that is causing an increasing number of weather extremes, has the less than catchy title of Quasi-resonant amplification of planetary waves and recent Northern Hemisphere weather extremes, and will be published this week in the US Proceedings of the National Academy of Sciences (link provided on publication).

The paper suggests that man-made climate change is repeatedly disturbing the patterns of airflow around the northern hemisphere, bringing extreme conditions.

This airflow has always travelled in waves round the planet, the wave movements caused by the difference in temperature between the oceans and land surfaces. These in turn cause changes in the high altitude air currents, particularly the jet stream.

Lead author Vladimir Petoukhov explains: “An important part of the global air motion in the mid-latitudes of the Earth normally takes the form of waves wandering around the planet, oscillating between the tropical and the Arctic regions.

“So when they swing up, these waves suck warm air from the tropics to Europe, Russia, or the US, and when they swing down, they do the same thing with cold air from the Arctic.

“What we found is that during several recent extreme weather events, these waves almost freeze in their tracks for weeks. So instead of bringing in cool air after having brought warm air in, the heat just stays. In fact we observe a strong amplification of the usually weak, slow-moving component of these waves.”

Tested against the data

 

Time is critical here: two or three days of 30˚C are no problem, but 20 days or more lead to extreme heat stress, the authors say. Since many ecosystems and cities are not adapted to temperatures this high, prolonged hot periods can cause many deaths, as well as forest fires and serious crop losses.

Climate change caused by greenhouse gas emissions from the burning of fossil fuels does not mean uniform warming – in the Arctic the relative rise in temperatures, amplified by the loss of snow and ice, is higher than average.

This in turn reduces the temperature difference between the Arctic and, for example, Europe. Yet it is this temperature difference that is normally a main driver of airflow, including the jet streams.

Additionally, continents generally warm and cool more readily than the oceans. They always have. But, coupled with the new changes to the jet streams, the net result is to trap the energy of the slow-moving parts of the waves.

“These two factors are crucial for the mechanism we detected,” says Petoukhov. “They result in an unnatural pattern of the mid-latitude airflow, so that for extended periods the slow waves get trapped.”

The authors tested their assumptions using standard daily weather data from the US National Centers for Environmental Prediction (NCEP). During recent periods in which several major weather extremes occurred, they did observe the trapping and strong amplification of particular waves.

‘A breakthrough’

 

The data show an increase in the occurrence of these specific atmospheric patterns which is statistically significant at the 90% confidence level.

“Our dynamical analysis helps to explain the increasing number of novel weather extremes. It complements previous research that linked such phenomena to climate change, but had not yet identified a mechanism behind it”, says Hans Joachim Schellnhuber, director of PIK and co-author of the study.

“This is quite a breakthrough, even though things are not at all simple – the suggested physical process increases the probability of weather extremes, but additional factors certainly play a role as well, including natural variability.”

The 32-year period of the project provides a good indication of the mechanism involved but is too short to allow definite conclusions.

Still, scientists are surprised by how far beyond experience some of the recent extremes have been. The new data show that the emergence of extraordinary weather is not just a straightforward linear response to the average warming trend, and the proposed mechanism could explain that. – Climate News Network

EMBARGOED until 2000 GMT on Monday 25 February
Extreme weather is often the result of climate change, according to scientists in Germany, who say they have found how greenhouse gases are helping to trap the jet stream and the weather patterns it brings.

LONDON, 25 February – The cause of much of the recent extreme weather across the world is climate change triggered by human activities, scientists say.

The Earth has experienced a range of severe regional weather extremes in recent years, including the heat waves of 2011 in the US and 2010 in Russia, a year that also brought the unprecedented Pakistan floods.

Behind these distinct events, though, there is a common physical cause, according to a team at the Potsdam Institute for Climate Impact Research (PIK), Germany.

Their paper, which helps to explain the mechanism that is causing an increasing number of weather extremes, has the less than catchy title of Quasi-resonant amplification of planetary waves and recent Northern Hemisphere weather extremes, and will be published this week in the US Proceedings of the National Academy of Sciences (link provided on publication).

The paper suggests that man-made climate change is repeatedly disturbing the patterns of airflow around the northern hemisphere, bringing extreme conditions.

This airflow has always travelled in waves round the planet, the wave movements caused by the difference in temperature between the oceans and land surfaces. These in turn cause changes in the high altitude air currents, particularly the jet stream.

Lead author Vladimir Petoukhov explains: “An important part of the global air motion in the mid-latitudes of the Earth normally takes the form of waves wandering around the planet, oscillating between the tropical and the Arctic regions.

“So when they swing up, these waves suck warm air from the tropics to Europe, Russia, or the US, and when they swing down, they do the same thing with cold air from the Arctic.

“What we found is that during several recent extreme weather events, these waves almost freeze in their tracks for weeks. So instead of bringing in cool air after having brought warm air in, the heat just stays. In fact we observe a strong amplification of the usually weak, slow-moving component of these waves.”

Tested against the data

 

Time is critical here: two or three days of 30˚C are no problem, but 20 days or more lead to extreme heat stress, the authors say. Since many ecosystems and cities are not adapted to temperatures this high, prolonged hot periods can cause many deaths, as well as forest fires and serious crop losses.

Climate change caused by greenhouse gas emissions from the burning of fossil fuels does not mean uniform warming – in the Arctic the relative rise in temperatures, amplified by the loss of snow and ice, is higher than average.

This in turn reduces the temperature difference between the Arctic and, for example, Europe. Yet it is this temperature difference that is normally a main driver of airflow, including the jet streams.

Additionally, continents generally warm and cool more readily than the oceans. They always have. But, coupled with the new changes to the jet streams, the net result is to trap the energy of the slow-moving parts of the waves.

“These two factors are crucial for the mechanism we detected,” says Petoukhov. “They result in an unnatural pattern of the mid-latitude airflow, so that for extended periods the slow waves get trapped.”

The authors tested their assumptions using standard daily weather data from the US National Centers for Environmental Prediction (NCEP). During recent periods in which several major weather extremes occurred, they did observe the trapping and strong amplification of particular waves.

‘A breakthrough’

 

The data show an increase in the occurrence of these specific atmospheric patterns which is statistically significant at the 90% confidence level.

“Our dynamical analysis helps to explain the increasing number of novel weather extremes. It complements previous research that linked such phenomena to climate change, but had not yet identified a mechanism behind it”, says Hans Joachim Schellnhuber, director of PIK and co-author of the study.

“This is quite a breakthrough, even though things are not at all simple – the suggested physical process increases the probability of weather extremes, but additional factors certainly play a role as well, including natural variability.”

The 32-year period of the project provides a good indication of the mechanism involved but is too short to allow definite conclusions.

Still, scientists are surprised by how far beyond experience some of the recent extremes have been. The new data show that the emergence of extraordinary weather is not just a straightforward linear response to the average warming trend, and the proposed mechanism could explain that. – Climate News Network