Many think the Younger Dryas event was due to the rush of fresh water as ice dams let loose the water from the great lakes.and lake agazzi. Massive cold likely killed off the clovis people and many plants and animals.12,900 years ago when the north Atlantic circulation was interrupted in the manner you described. A.most unwelcome consequence and feedback mechanism of climate change if correct.
New studies deepen concerns about a climate-change ‘wild card’ September 7, 2015 http://www.washingtonpost.com/news/energy-environment/wp/2015/09/07/new-studies-deepen-concerns-about-a-climate-change-wild-card/ [with comments] studies: Response of Atlantic overturning to future warming in a coupled atmosphere-ocean-ice sheet model First published: 28 August 2015 Abstract Climate change can influence sea surface conditions and the melting rates of ice sheets; resulting in decreased deep water formation rates and ultimately affecting the strength of the Atlantic Meridional Overturning Circulation (AMOC). As such, a detailed study of the interactive role of dynamic ice sheets on the AMOC and therefore on global climate is required. We utilize a climate model in combination with a dynamic ice sheet model to investigate changes to the AMOC and North Atlantic climate in response to Intergovernmental Panel on Climate Change scenarios for RCP4.5 and RCP6. It is demonstrated that the inclusion of an ice sheet component results in a drastic freshening of the North Atlantic by up to 2 practical salinity units, enhancing high-latitude haloclines and weakening the AMOC by up to 2 sverdrup (106 m3/s). Incorporating a bidirectionally coupled dynamic ice sheet results in relatively reduced warming over Europe due to the associated decrease in heat transport. http://onlinelibrary.wiley.com/doi/10.1002/2015GL065276/full Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics Published 02 September 2015 Abstract Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10–100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland. http://www.nature.com/ncomms/2015/150902/ncomms9061/full/ncomms9061.html [and see DesertDrifter's reply to the post to which this is a reply at http://investorshub.advfn.com/boards/read_msg.aspx?message_id=117792784 ]
Wobbly Jet Stream Is Sending the Melting Arctic into 'Uncharted Territory'
A shift in weather patterns created a month of extreme melting, prompting scientists' concern about the impact on long-term climate models.
By Bob Berwyn, Inside Climate News Jun 9, 2016
Extreme melting in parts of Greenland have been tied to jet stream shifts
Extreme melting in Greenland's ice sheet last summer was linked to warm air delivered by the wandering jet stream (seen here), which has been linked to extreme warming in the Arctic. Credit: NASA
Extraordinary melting in Greenland's ice sheet last summer was linked to warm air delivered by the wandering jet stream, a phenomenon that scientists have increasingly tied to global warming.
This interplay of climate phenomena, described in a new study in the journal Nature Communications, is more evidence of the complex ways in which the Arctic's climate is heading for "uncharted territory," said the study's lead author, Marco Tedesco.
The study adds to an emerging theory on the effects of the pronounced warming of the Arctic, where temperatures are rising faster than in more temperate zones, as models have long predicted. Known as "Arctic amplification," this moderates the normal temperature incline that drives the jet stream. If it makes the jet stream wobble, as some scientists suspect, it would suck warm air up into the Arctic—as was observed in Greenland last year.
The new study analyzes the severe shift in wind patterns last July that transported huge masses of warm, moist air from the Atlantic to the Arctic, dramatically melting the northern reaches of the ice sheet. Never before has the jet stream been seen to intrude so far into the Arctic during the summer, the scientists reported.
Accounting for these shifts is crucial to being able to model how much sea level will rise and how fast. Greenland's melting is one of the biggest contributors to rising seas, and if its ice were to disappear completely it could raise global sea level by as much as 20 feet .. https://nsidc.org/cryosphere/quickfacts/icesheets.html .
An extreme melting event in part of Greenland's ice sheets has scientists worried about long-term impacts. Credit: Getty Images
"The models are not capturing these extreme events like the July melting," said Marco Tedesco, the study's lead author. "If we are changing the atmosphere in a way that has not been happening before, with greenhouse gases, then even if we have the tools to make projections based on observations, we won't know how to model for the future." Tedesco is a geophysicist with Columbia University's Lamont-Doherty Earth Observatory .. http://www.ldeo.columbia.edu/climate-center .
The unusual weather last July included a strong and persistent area of high pressure over Greenland. It led to new records in northwestern Greenland's surface temperature, melting and runoff, as well as record albedo loss—a darkening of the ice that increases heat absorption and accelerates melting.
It was also just one example of the profound influences flowing from changes in the jet stream, a river of air flowing east to west in a sinuous pattern around the northern hemisphere. In recent years, its wavy line has drifted farther north and south than usual.
Some researchers say these changes can explain intense warming in Alaska, the "polar vortex" weather that has frozen parts of the United States, as well as stronger storms in some regions and variations in tropical monsoons.
"Our results show the effects of a strongly warming Arctic and disturbed atmospheric jet stream on causing a record melt of the far northern reaches of the Greenland ice sheet last summer," said Edward Hanna, a climate change researcher at the University of Sheffield who was part of the research. In a previous study .. http://onlinelibrary.wiley.com/doi/10.1002/joc.3743/abstract , Hanna also linked extreme Greenland ice sheet melting in 2012 to an unusual northward loop of the jet stream.
Overall in the summer of 2015, the melt season was about 30 to 40 days longer than average in the western, northwestern and northeastern regions of Greenland. For the first time since 2012, the melt area exceeded more than half the ice sheet.
Tedesco's study focused on the July 2015 heat wave in Greenland, but the jet stream continued to surprise researchers in the following months. Last winter, it again veered far northward, nearly brushing the North Pole, said Rutgers University climate researcher Jennifer Francis, a leading theorist of the far-reaching effects of Arctic amplification.
"The inference is, there is a clear mechanism here, and we should probably expect to see these big melting events on the surface of the Greenland Ice Sheet more frequently," she said.
That pattern was common last winter and led to record-high temperatures over large parts of the Arctic—including Greenland—that persisted for weeks and inhibited sea ice growth, according to the regular updates posted by the National Snow and Ice Data Center .. http://nsidc.org/ . Large areas of the Arctic reported the warmest conditions in 67 years of weather data, including the northern half of the Greenland ice sheet, U.S. ice researchers said on the Greenland Ice Sheet today website .. http://nsidc.org/greenland-today/ .. in April.
Extreme twists in the jet stream recurred this spring, and according to the National Snow and Ice Data Center .. http://nsidc.org/greenland-today/ , the Greenland ice sheet melt season started early, in April, with melting across about 10 percent of the sheet. Such early melting has only been observed a few times since satellites started measuring it accurately in 1979.
A separate study, published in April in the International Journal of Climatology .. http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291097-0088 , found that stationary, or blocking, high pressure systems have become more frequent over Greenland since the 1980s. That research, by University of Sheffield scientists also linked the recurrence with flooding in Great Britain in 2007 and 2012.
Other researchers said the new study helps broaden the understanding of how atmospheric patterns will affect the Arctic in the long term.
Dirk Notz, director of the Arctic sea ice research unit at the Max-Planck Institute for Meteorology .. http://www.mpimet.mpg.de/mpimet-startseite/ .. in Hamburg, Germany, said he's not convinced that the recent jet stream shifts are directly linked to global warming, but said the new study is part of an important effort to explain connections between changes in atmospheric patterns and extreme climate changes.
"We need to understand why things happen," Notz said. "I think there's a public perception that Arctic science focuses on monitoring only extreme events. That's a dangerous perception, because even if there's a record sea ice low this year, it will probably recover. From a science perspective, it's not the extreme events that are most interesting but the long-term trends."
Carbon dioxide—a heat-trapping gas produced by burning fossil fuels—is the primary driver of global warming. Carbon dioxide levels have been on the rise all over the world, but because Antarctica is so remote, the pollutant has accumulated more slowly there. Antarctic CO2 concentrations first surpassed the 400 ppm mark on May 23, according to measurements taken at the South Pole Observatory.
National Oceanic and Atmospheric Administration
"The far southern hemisphere was the last place on earth where CO2 had not yet reached this mark," Pieter Tans, the lead scientist of NOAA's Global Greenhouse Gas Reference Network, said in a statement. "Global CO2 levels will not return to values below 400 ppm in our lifetimes, and almost certainly for much longer."
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