Jet stream changes cause climatically exceptional Greenland Ice Sheet melt

The edge of the GrIS.

from University of Sheffield News, June 17, 2013

Research from the University of Sheffield has shown that unusual changes in atmospheric jet stream circulation caused the exceptional surface melt of the Greenland Ice Sheet (GrIS) in summer 2012.

An international team led by Professor Edward Hanna from the University of Sheffield’s Department of Geography used a computer model simulation (called SnowModel) and satellite data to confirm a record surface melting of the GrIS for at least the last 50 years -- when on 11 July 2012 more than 90% of the ice-sheet surface melted. This far exceeded the previous surface melt extent record of 52% in 2010.

The team also analysed weather station data from on top of and around the GrIS, largely collected by the Danish Meteorological Institute but also by US programmes, which showed that several new high Greenland temperature records were set in summer 2012.

The research, published today in the International Journal of Climatology, clearly demonstrates that the record surface melting of the GrIS was mainly caused by highly unusual atmospheric circulation and jet stream changes, which were also responsible for last summer's unusually wet weather in England.

The analysis shows that ocean temperatures and Arctic sea-ice cover were relatively unimportant factors in causing the extra Greenland melt.

Professor Hanna said: “The GrIS is a highly sensitive indicator of regional and global climate change, and has been undergoing rapid warming and mass loss during the last 5-20 years. Much attention has been given to the NASA announcement of record surface melting of the GrIS in mid-July 2012. This event was unprecedented in the satellite record of observations dating back to the 1970s and probably unlikely to have occurred previously for well over a century.

“Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting. These jet stream changes over Greenland do not seem to be well captured in the latest Intergovernmental Panel on Climate Change (IPCC) computer model predictions of climate change, and this may indicate a deficiency in these models. According to our current understanding, the unusual atmospheric circulation and consequent warm conditions of summer 2012 do not appear to be climatically representative of future ‘average’ summers predicted later this century.

“Taken together, our present results strongly suggest that the main forcing of the extreme GrIS surface melt in July 2012 was atmospheric, linked with changes in the summer North Atlantic Oscillation (NAO), Greenland Blocking Index (GBI: a high-pressure system centred over Greenland) and polar jet stream which favoured southerly warm air advection along the western coast.

“The next 5-10 years will reveal whether or not 2012 was a rare event resulting from the natural variability of the NAO or part of an emerging pattern of new extreme high melt years. Because such atmospheric, and resulting GrIS surface climate, changes are not well projected by the current generation of global climate models, it is currently very hard to predict future changes in Greenland climate. Yet it is crucial to understand such changes much better if we are to have any hope of reliably predicting future changes in GrIS mass balance, which is likely to be a dominant contributor to global sea-level change over the next 100-1,000 years.”

http://www.shef.ac.uk/news/nr/jet-stream-greenland-ice-sheet-melt-1.280360

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Jeff Masters: Extreme weather whiplash in the Upper Midwest -- Climate change much?

by Jeff Masters and Christopher C. Burt, Wunderground Blog, May 15, 2013

Does not compute! That must be what residents of Iowa and the Midwest have have been saying to themselves on Tuesday as a ferocious heat wave unprecedented in intensity for so early in the year sent temperatures soaring as high as 108 °F. Just two weeks ago, the deepest snowfall ever measured during any May of record buried a wide swath from Arkansas to Minnesota, with Iowa breaking its all-time snowfall record for May (13” accumulation at Osage on May 1-3.) And how's this for a definition of "Weather Whiplash": Sioux City, Iowa, had their first-ever snowfall on record in the month of May on May 1st (1.4"), but hit an astonishing 106 °F yesterday. Not only was this their hottest temperature ever measured in the month of May, but only two June days in recorded history have been hotter (June, 10, 1933: 107 °F; and June 21, 1988: 108 °F). On May 12th they registered 29 °F, and thus had a 77-degree rise over 56 hours (from 6 a.m. May 12 to 1:30 p.m May 14.)


Figure 1. Intense heat and strong winds fanned a wildfire in northwestern Wisconsin's Douglas County near Gordon on Tuesday, May 14, 2013. The fire spread to 8,700 acres and forced dozens of residents to leave their homes. Image credit: Kevin Harter/Wisconsin Department of Natural Resources, and courtesy of wisconsinrapidstribune.com.

The hottest temperature of all on Tuesday was 108 °F at Tekamah, Nebraska. This is just 2 degrees short of warmest temperature ever recorded in the state of Nebraska during May: 110 °F at Broken Bow in 1895 (exact day unknown). Numerous all-time early season heat records were set on Tuesday, making the event the most notable May wave in the Midwest since multi-day event in 1934. That heat wave was not preceded by unusually cold weather, which is what makes the May 2013 Midwest heat event truly extraordinary. A few notable cases of "Weather Whiplash" from the May 14, 2013, heat wave:

- Chicago, Illinois, hit 91 °F, after hitting a low of 36 °F the previous morning. The 1-day temperature swing of 52 degrees was the city's greatest on record for the month of May.

- Rochester, Minnesota, where 14.5” of snow fell just 10-12 days ago (4th greatest snowstorm for any month on record), saw an all-time early season heat record of 97 °F on May 14th. The previous day, May 13th, it was 32 °F in Rochester -- a 65-degree rise in temperature over the course of 36 hours. 

- Omaha, Nebraska, hit 101 °F, the earliest 100 °F on record (old record was 102 °F on May 29, 1934). It was 32 °F in Omaha on May 12th! That tied for the coldest so late in the season with 32 °F on May 13, 1997, and also on May 15, 1983.

- Albert Lea and St. James, Minnesota, hit 102 °F (hottest in the state on Tuesday). Both cities had May snow less than two weeks previously. Tuesday morning, it was 27 °F at Crane Lake and Silver Bay, for a same-day state temperature spread of 75 degrees in Minnesota. This is a relatively common figure for California or Texas, but almost unprecedented for a Midwestern state.

- Minneapolis hit 98 °F, the hottest so early in season (next is 99 °F on May 22, 1925). May record is 106 °F on May 31, 1934 (the only time 100 °F has been measured during May).

- Norfolk, Nebraska, hit 103 °F, the hottest temperature ever measured so early in the year (previous record: 103 °F on May 25, 1967). A daily record low of 29 °F was recorded on May 12th, just two days previous.

Fires in Wisconsin and Minnesota
The intense heat was accompanied by strong winds, which fanned multiple fires in Minnesota and Wisconsin. One fire, near Gordon, Wisconsin, burned 8,700 acres, making it the largest fire in Wisconsin since the Cottonville fire on May 5, 2005, and the largest fire in Northern Wisconsin since the Oak Lake fire of April 22, 1980 (11,418 acres.) The Gordon fire destroyed 47 structures, including 17 homes, and forced the evacuation of several dozen people. The fire was 90% contained Wednesday morning. At least 25 smaller wildfires were reported in Minnesota, and Governor Mark Dayton signed an emergency order on Tuesday to help the Minnesota Interagency Fire Center fight wildfires around the state.

Why the crazy extremes? Blame the jet stream
The position of the jet stream is a critical controller of weather regimes across the U.S., Europe, and Asia. Precipitation-bearing low pressure system ride along the axis of the jet, and the jet marks the boundary between cold, Canadian air to the north, and warm, subtropical air to the south. On average, the jet flows from west to east, but the jet often departs from average. The jet is continually rippling with U-shaped troughs of low pressure that allow cold air to spill southwards. The troughs are counterbalanced by upside-down-U-shaped ridges of high pressure that bring warm air northwards. When these ridges and troughs grow to unusually large amplitude, record extremes of both cold and heat occur adjacent to each other. Often times, the jet will have multiple extreme loops that result in unusual extremes over large portions of the Northern Hemisphere. That was the case Tuesday in Europe, where an unusually strong ridge of high pressure was present over Western Russia, with a companion strong trough of low pressure over the UK.  Moscow hit 29.7 °C (85.5 °F) on Tuesday, and several locations within the city rose to 31 °C (88 °F). According to weather records researcher Maximiliano Herrera, this has never happened in the first half of May before. At the same time, up to 3" of snow fell in the UK on Tuesday, a rare occurrence for mid-May. Could climate change be a factor in the extreme gyrations of the jet stream this year? It could, and I discussed some of the possible connections in my April 2013 post: Unusually cold spring in Europe and the Southeast U.S. due to the Arctic Oscillation.


Figure 2. Monday afternoon's jet stream shows the pronounced ridge (upside-down U-shaped curve to the jet stream) over the midwestern U.S., which led to all-time, record-high temperatures for so early in the year. At the same time, a sharp trough of low pressure (U-shaped dip in the jet stream) was present over the East Coast, which allowed cold air from Canada to spill southwards and set record lows -- for example, 44 °F at Tallahassee, Florida on May 14, 2013.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2407

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This isn't the weather we grew up with by John Abraham, Climate Consensus -- The 97%, The Guardian

Climate change means we are experiencing extreme weather with increasing frequency – and increasing economic cost
 

Floodwaters from hurricane Sandy rush down an elevator shaft into Hoboken PATH station in New York. Photograph: Reuters/Port Authority Trans-Hudson

by John Abraham, "Climate Consensus - The 97%", The Guardian, May 7, 2013

It doesn't take a rocket scientist (or an earth scientist for that matter) to know that today's weather isn't the weather we grew up with – and today's climate isn't the climate of yesterday. As a scientist who studies this topic daily, I and my colleagues know why. Human greenhouse gas emissions have led to a 40% increase in the amount of carbon dioxide in the atmosphere. As a result, the Earth is gaining energy at an alarming rate.

So what? How will all this energy change the climate (and the weather we experience)? Well some changes are pretty straightforward… First scientists expect that the Earth will globally get warmer, although the warming will happen much faster in some areas than others. We expect the rate of drying (and consequently drought) will increase in some areas while other regions will become wetter with more flooding. We expect to lose ice, see oceans rise, changes to the ocean acidity level, among other changes.

Some changes, however, have been harder to unearth but recent exciting findings are shining some illumination. Among the most exciting areas of research is the connection between loss of arctic sea ice and extreme weather in the Northern Hemisphere. The arctic, which has been warming at an alarming rate has seen an approximately 75% decrease in the summer sea ice volume. Consequently arctic waters, which had been covered by ice, are now absorbing tremendous amounts of solar energy during the summer and releasing it to the atmosphere during the autumn and early winter.

This change in the arctic energy balance has begun to have an effect on the weather patterns, particularly on the jet stream. This rapidly flowing stream of high-altitude air separates the cold dry arctic air from warmer moist air closer to the equator. When that jet stream dips southward, watch out! Cold air and potential downpours or snow storms may be coming your way. Recently, the jet stream has been more likely to be found in an undulating, slowly moving state.

NASA image of meandering polar jet stream

What does this mean to us? It means that we shouldn't be surprised to see more severe weather that lasts for longer durations. Our weather can be expected to whiplash from one extreme to another.

In the U.S. we are seeing some evidence of this. Alternating wet, snowy winters and warm non-winters. Summers of either extreme heat and drought – or unbelievable flooding.

But don't just take my word for it. A leading researcher in this area, Dr. Jennifer Francis says,

The Arctic is warming two-to-three times faster than the rest of the northern hemisphere -- the loss of sea ice, spring snow cover, increased Greenland melting, and permafrost degradation are all symptoms of and contributors to this warming. It's inconceivable that a change of this scale and magnitude will not have substantial impacts on the atmosphere, ocean, and land both within the Arctic and also beyond the Arctic where millions of people live. These impacts will affect not only the physical system -- such as weather patterns and ocean circulation -- but also life on land and in the ocean. Exactly how these effects play out is a wide-open topic of research.

Jennifer Francis

Regarding the specific impact of global warming on Superstorm Sandy, her colleague, Dr. Charles Greene added,

Images of flooded subway stations in New York City, demolished towns on the New Jersey shore, and autumn blizzard conditions in Appalachia will be etched in the nation's psyche for quite some time. With the increasing frequency of extreme weather events serving as a backdrop, many people are asking what role, if any, did anthropogenic climate change play in the development of Superstorm Sandy? If one takes into account the record loss of Arctic sea ice this past September, then perhaps the likelihood of greenhouse warming playing a significant role in Sandy's evolution as an extra-tropical superstorm is at least as plausible as the idea that (she) was simply a freak of nature.

Charles Greene

If we are seeing this type of extreme weather already, it makes one wonder what the world will be like in 10, 20, or 50 years. We will certainly have to deal with many more costly weather disasters. More European heat waves like 2003 or 2010; more Midwest United States droughts of 2011 and 2012. Repeated 1000 year floods, larger storms like Sandy, and yes…. We will even see snow… lots of it. Charles Greene's November 2012 Scientific American paper was prescient – he virtually predicted the extreme weather, including Sandy and the series of nor'easters that have battered the Eastern Seaboard this past winter. It makes one wonder about other events. The alternating years of droughts and floods in the Midwest that have converted last year's severe dryout into today's severe floods in Indiana and Illinois? Are they tied to human emissions? What about the oscillating heat waves/drought and flooding episodes in Australia? We can only hope that this emerging science continues to advance so that these questions can be answered.

There are two takeaway messages to all of this. First, all of today's weather is now affected by climate change. Second, there is a tremendous cost to the extremes we are seeing. For those who say taking action to stop climate change is too expensive, we only have to point to the costs we are incurring right now. It is clear that it is too expensive to ignore this problem.

But don't just take it from me, ask my students. Engineering student Sara Backlund, who attends my heat transfer course recently remarked,

Last summer was crazy hot – so hot my soccer games had to be cut short. This spring it is incredibly cold – it's May and we haven't even started practicing and our games are being canceled. Even I can see the weather is changing…

So, it may not take a rocket scientist to tell us we're changing the weather… It might just take a bright engineering student.

• Dr. John Abraham of University of St. Thomas, the Climate Science Rapid Response Team and the Climate Science Legal Defense Fund

http://www.guardian.co.uk/environment/climate-consensus-97-per-cent/2013/may/07/isnt-weather-we-grew-up-with

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Peter Sinclair: Jet Stream Blows Winds of Change

by Peter Sinclair, Climate Denial Crock of the Week, April 19, 2013

I’ve been recovering from earth-month speaking-event whiplash, having criss-crossed the state over recent days to talk about climate change, and what scientists are telling us.

Meanwhile, Paul Douglas, above, gave a brief summary of what we know about the extreme spring in the US, just before the current river of moisture hit across the nation’s midsection last night.


Near record setting flooding is hitting at my location, schools closed and evacuations underway.  I got a bump from Jeff Masters last night about the situation, he is grappling with the big picture, will be posting more later today.  For now, more concern about extreme weather knock-on effects – possible washing of dangerous invasive species into the Great Lakes water system.

WeatherUnderground:

The rains have brought the Des Plaines River on the east side of Chicago to major flood stage this morning, and a record flood crest is expected on Friday. The Asian Carp, a dangerous invasive species that would cost billions of dollars were it to get loose in the Great Lakes, is present in the Des Plaines River. Today’s flood event is capable of washing significant numbers of Asian Carp from the Des Plaines River into a canal that feeds directly into Lake Michigan, where they might be able to set up a breeding population capable of devastating the Great Lakes’ fishing industry. However, in October 2010, the U.S. Army Corps of Engineers completed the Des Plaines River barricade, a 13-mile-long system of concrete barriers and a specially fabricated wire mesh that allows water to flow through the fence but prevents the passage of fish. Hopefully, this barricade will withstand the flood and prevent Asian Carp from washing into Lake Michigan.

CarbonBrief reports on similar extremes in northern Europe :

The Met Office has just released a report entitled “why was the start to spring 2013 so cold?”
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The immediate cause was a natural climate fluctuation called the North Atlantic Oscillation (NAO). The NAO switches between two states, and this winter (in its negative phase) saw a southward shift of the jet stream, bringing cold air over the UK from northern Europe and Russia. 

The Met Office identifies three other natural climate variations that may have made the negative NAO phase more likely. 

One is the recent behaviour of another natural climate fluctuation, called the Madden-Julian Oscillation (MJO). It was particularly strong during late February and March – often a sign that a negative NAO is on the way. 

This winter also saw what’s called a Sudden Stratospheric Warming (SSW) event, where winds in the stratosphere above the north pole reverse direction. This brought cold weather conditions to the UK. 

Finally, Europe’s climate is influenced by another natural climate system – the Atlantic Multi-decadal Oscillation (AMO). While the influence on UK winters is unclear, the report suggests: 

“[T]here is some evidence that the changes in Atlantic sea surface temperatures associated with the AMO, dispose the circulation to give drier than normal spring conditions over the UK and northern Europe.” 

Arctic Amplification
What about the effects of human-caused climate change? One question that has been much discussed recently is whether the recent rapid decline in Arctic sea ice could contribute to a change in the UK’s weather.

The new report explains how this could work: 

“It is argued that amplification of global warming over the Arctic is reducing the equator to pole temperature gradient, thereby weakening the strength of the mid-latitude jet streams.”

This could allow cold Arctic air to push further south, over mid-latitude countries like the UK, and weather patterns could stay longer in one place. 

The possibility of a link between the Arctic and UK weather appears to be gaining scientific support, but the Met Office acknowledges it’s still an “area of ongoing research.” The Met Office has told us it’s holding an “ informal workshop” in the next two to three months for leading UK scientists plus several international experts. 

Multiple factors
While scientists are making progress in working out how climate change could influence the odds of abnormal weather, it would be unwise to attribute one year’s events to a single cause. The report points this out, noting that: 

“…no single explanation can account for the cold conditions observed.” 

The report also highlights that although this spring was unusually cold,” it is not unprecedented or outside the expected natural variability of our climate.” 

Nevertheless, with what the Met Office describes as “particularly heightened interest” in recent weather, getting to grips with how climate change could be affecting things is important. Even if, as the Met Office suggests, the complexities of the UK weather make “communicating the science drivers more complicated and nuanced than some audiences may wish.”

 http://climatecrocks.com/2013/04/19/jet-stream-blows-winds-of-change/

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