2/4/17

Gulf Stream slowdown tied to changes in Southern Hemisphere



SCIENCE DAILY







Date:



October 5, 2016
Source:

University of Washington
Summary:
The ocean circulation that is responsible for England's mild climate appears to be slowing down. The shift is not sudden or dramatic, as in the 2004 sci-fi movie "The Day After Tomorrow," but it is a real effect that has consequences for the climates of eastern North America and Western Europe. Also unlike in that movie, and in theories of long-term climate change, these recent trends are not connected with the melting of the Arctic sea ice and buildup of freshwater near the North Pole. Instead, they seem to be connected to shifts at the southern end of the planet, according to a recent University of Washington study in the journal Geophysical Research Letters.
"It doesn't work like in the movie, of course," said Kathryn Kelly, an oceanographer at the UW's Applied Physics Laboratory. "The slowdown is actually happening very gradually, but it seems to be happening like predicted: It does seem to be spinning down."
The study looked at data from satellites and ocean sensors off Miami that have tracked what's known as the Atlantic overturning circulation for more than a decade. Together they show a definite slowdown since 2004, confirming a trend suspected before then from spottier data.
Looking at other observations to determine the cause, the researchers ruled out what had been the prime suspect until now: that massive melting and freshening in the North Atlantic could stop water from sinking and put the brakes on the overturning circulation, which moves warmer water north along the ocean's surface and sends cold water southward at depths.
"It appears that this 10-year slowdown is not related to salinity," Kelly said. In fact, despite more ice melt, surface water in the Arctic is getting saltier and therefore denser, she said, because of less precipitation. "That means the slowdown could not possibly be due to salinity -- it's just backwards. The North Atlantic has actually been getting saltier."
Instead, the authors saw a surprising connection with a current around the southern tip of South Africa. In what's known as the Agulhas Current, warm Indian Ocean water flows south along the African coast and around the continent's tip toward the Atlantic, but then makes a sharp turn back to join the stormy southern circumpolar current. Warm water that escapes into the Atlantic around the cape of South Africa is known as the Agulhas Leakage. The new research shows the amount of leakage changes with the quantity of heat transported northward by the overturning circulation.
"We've found that the two are connected, but I don't think we've found that one causes the other," Kelly said. "It's more likely that whatever changed the Agulhas changed the whole system."
She believes atmospheric changes may be affecting both currents simultaneously.
"Most people have thought this current should be driven by a salinity change, but maybe it's the [Southern Ocean] winds," Kelly said.
The finding could have implications for northern European and eastern U.S. climates, and for understanding how the world's oceans carry heat from the tropics toward the poles.
"I think it changes how we think about the whole Atlantic overturning circulation, of which the Gulf Stream is a part," said co-author LuAnne Thompson, a UW professor of oceanography. "It brings back the role of the atmosphere into what's controlling the climate in the high latitudes, that it's not all driven by what's happening in the oceans."
And while a slowdown of the Gulf Stream and broader overturning circulation, for whatever reason, would bring less warm water to eastern North America and Western Europe, any effects are overwhelmed by the overall warming due to global climate change.
"So that whole concept in the movie of New York harbor freezing doesn't make any sense," Kelly said. "If the Gulf Stream doesn't carry as much heat from the tropics, it just means that the North Atlantic is not going to warm up as fast as the rest of the ocean -- it's not going to cool down."

Story Source:
Materials provided by University of WashingtonNote: Content may be edited for style and length.

Journal Reference:
  1. Kathryn A. Kelly, Kyla Drushka, LuAnne Thompson, Dewi Le Bars, Elaine L. McDonagh. Impact of slowdown of Atlantic overturning circulation on heat and freshwater transportsGeophysical Research Letters, 2016; 43 (14): 7625 DOI: 10.1002/2016GL069789

Cite This Page:
University of Washington. "Gulf Stream slowdown tied to changes in Southern Hemisphere." ScienceDaily. ScienceDaily, 5 October 2016. .









Danish Scientist Targets Claim that Gulf Stream Is Slowing


REUTERS   British Antartic Survey/Handout

A Danish climatologist is pouring cold water over another misleading global warming claim.

Thermographic images released by the National Oceanic and Atmospheric Administration (NOAA) last year showed a mysterious blue blob of cold seawater off the coast of southern Greenland and Iceland. At the time, researchers said the cold blob was likely the result of melting from Greenland’s vast ice sheet, with cold water flowing into the nearby Labrador Sea.
This meltwater was presumed to have slowed the Atlantic Meridional Overturning Circulation (AMOC), or Gulf Stream, that sustains temperate weather in much of western Europe, our East Coast, and the UK.

One of the first researchers at the trough of misinformation was Prof. Michael Mann of Pennsylvania State (and “Hockey Stick” fame), who told the Washington Post that this North Atlantic cold blob happened to fit with his just-published study. Mann also suggested that a “dramatic melting” of Greenland’s ice sheet would slow or stop the AMOC, sending the world into an abrupt climate shift as seen in the climatastrophe flick The Day After Tomorrow.
But Tor Eldevik, a Norwegian climate researcher and professor, subsequently told the newspaper Aftenposten in March 2016 that he was “not convinced that the blue blob was caused by melting Greenlandic ice.” Or that it was slowing the Gulf Stream.
Eldevik said that affecting the AMOC would require vast amounts of freshwater coming into contact with more saline ocean water, which would dramatically change salinity levels and possibly slow the current down. That theory might make sense, Eldevik said, except the currents around Greenland simply aren’t strong enough, or large enough, to slow or stop the Gulf Stream.
Another climate researcher, Peter Langen, showed that this melting Greenlandic ice claim has nothing to do with global warming but rather the result of a particularly cold winter. Dr. Langen, a climatologist at the Danish Meteorological Institute (DMI), said that while Greenland’s coastal areas are melting a little, there simply hasn’t been enough freshwater released to affect the ocean’s circulation in any significant way.
In fact, a year-long study of Greenland’s interior ice sheet showed how very little precipitation is lost via evaporation or melting due to the island’s unique “thermal lid.”
The study, published in Science Advances, illustrates how this unique thermal lid prevents snow and ice from escaping the island, allowing the ice sheet to continuously accumulate in mass. And despite computer climate models claiming Greenland’s ice sheet would be one of the first fatalities in a warming world, this first-of-its-kind study offers convincing evidence that Greenland’s ice sheet remains robust and stable.
Langen also noted that ocean modeling from various studies shows that there simply isn’t enough freshwater being released to influence the Gulf Stream at any great distance from Greenland. After reviewing two new studies, Langen adds that the cold spot seen on NOAA’s map is most likely the result of a simple weather anomaly: an unusually cold winter.
Langen says if the cause of the cold blob was meltwater, it would get mixed and thinned out. The Labrador Sea, which is southwest of Greenland’s southern tip, helps to mix surface and deep ocean water. The saltier the water, the more mixing occurs. If the salinity decreases, so does the mixing. Put simply, the freshwater becomes diluted in such a large area that it is unable to slow or stop oceanic circulation.
Langen adds that the blue blob showed up on NOAA’s maps during the very cold winter of 2014-2015, and the frigid weather actually resulted in increased mixing of surface water with the cold, deep seawater. Langen also explained that researchers reconstructed the cooling of water in the area through complex energy computations, making the weather theory the strongest, and most likely, explanation for the North Atlantic cold blob.
It appears that the cold water observed in the North Atlantic was simply due to a cold winter. And yet, climate alarmists readily attempted to spin it into further proof of global warming. But an analysis of the data shows that, once again, such dramatic claims were overstated.
Thomas Richard is a freelance writer living outside of Boston, MA.

Gulf stream slowdown to spare Europe from worst of climate change


PHYS.ORG

11 de julio de, 2016 James Hakner

The Thermohaline Circulation is a vast system of ocean currents that operates like a conveyor belt, transporting warm water from the tropics to Europe. Credit: istockphoto.com/aristoo

Read more at: https://phys.org/news/2016-07-gulf-stream-slowdown-europe-worst.html#jCp

Europe will be spared the worst economic impacts of climate change by a slowing down of the Gulf Stream, new research predicts.


Scientists have long suggested that global warming could lead to a slowdown – or even shutdown – of the vast system of ocean currents, including the Gulf Stream, that keeps Europe warm.
Known as the Thermohaline Circulation, this system operates like a conveyor belt, transporting warm water from the tropics to Europe, where evaporation decreases salinity and density so that the water sinks.
As the world warms, melting icecaps and increased rainfall are widely predicted to slow this process down by flooding oceans with cold freshwater.
Some experts even fear that the process could shut down altogether, plunging Europe into a new ice age.
However, a new study by the University of Sussex, Universidad Nacional Autónoma de México and the University of California, Berkeley finds that, rather than cooling Europe, a slowdown of the Thermohaline Circulation would mean the continent still warms, but less quickly than other parts of the world.
This would lead to a rise in welfare standards in Europe, concludes the research, which is published in the leading economics journal the American Economic Review.
Professor Tol, Professor of Economics in the School of Business, Management and Economics at the University of Sussex, said: "Cooling is probably a good bit more harmful than warming, particularly in Europe. People rightly fear that climate change would cause a new ice age.
"Fortunately, our study finds no cooling at all. Instead, we find slower warming: a boon for Europeans."
Of course, as  redistribute rather than create heat, slower warming for Europe means slightly accelerated warming elsewhere.
The study, therefore, adds to a growing body of evidence predicting a rich/poor divide in the  stakes. Developing countries will be less able to cope with rising sea levels, for example, and - as this research suggests - may warm faster than other, more developed parts of the world.
More information: David Anthoff et al. Shutting Down the Thermohaline Circulation, American Economic Review (2016). DOI: 10.1257/aer.p20161102 



Read more at: https://phys.org/news/2016-07-gulf-stream-slowdown-europe-worst.html#jCp

Gulf Stream is slowing down faster than ever, scientists say

INDEPENDENT



The Gulf Stream that helps to keep Britain from freezing over in winter is slowing down faster now than at any time in the past millennium according to a study suggesting that major changes are taking place to the ocean currents of the North Atlantic.
Scientists believe that the huge volumes of freshwater flowing into the North Atlantic from the rapidly melting ice cap of Greenland have slowed down the ocean “engine” that drives the Gulf Stream from the Caribbean towards north-west Europe, bringing heat equivalent to the output of a million power stations.
Scientists believe that huge volumes of freshwater flowing into the North Atlantic from the rapidly melting ice cap of Greenland have slowed down the ocean “engine” that drives the Gulf Stream (Getty)

However, the researchers believe that Britain is still likely to become warmer due to climate change providing the Gulf Stream does not come to a complete halt – although they remain unsure how likely this is.
Calculations suggest that over the 20th century the North Atlantic meridional overturning circulation – the northward flow of warm surface water and the southward flow of deep, cold water – has slowed by between 15 and 20 per cent, said Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.
“There is more than a 99 per cent probability that this slowdown is unique over the period we looked at since 900 AD. We conclude that the slowdown many have described is in fact already underway and it is outside of any natural variation,” Professor Rahmstorf said.
The scientists calculated that some 8,000 cubic kilometres of freshwater has flowed from Greenland into the Atlantic between 1900 and 1970, and this rose significantly to 13,000 cubic kilometres between 1970 and 2000.
Freshwater is lighter than salty water which means that it tends to float on the surface of the ocean and in doing so disturbs the normal sinking of dense, cold saltwater to the ocean floor, which is the main driver of the Atlantic circulation.
Jason Box of the Geological Survey of Denmark and Greenland, who helped to calculate the amount of freshwater flowing into the Atlantic from melting ice caps, said that the slowdown can be linked to man-made climate change.
“Now freshwater coming off the Greenland ice sheet is likely disturbing the circulation. So the human-caused mass loss of the Greenland ice sheet appears to be slowing down the Atlantic overturning, and this effect might increase if temperatures are allowed to rise further,” Dr Box said.
Michael Mann of Pennsylvania State University said: “Common climate models are underestimating the change we’re facing, wither because the Atlantic overturning is too stable in the models or because they don’t properly account for Greenland ice melt, or both.”

15/9/16

“Efecto Ártico” Años muy cálidos, Inviernos muy fríos ¿Hacia una Pequeña Glaciación?

TIEMPO.COM


Inviernos extremos, repotenciados por el Mínimo Solar del 2020 podrían llevar al Hemisferio Norte a una “Pequeña Glaciación”

El "Efecto Ártico” (*)  es una hipótesis que sostengo desde el 2 de diciembre de 2002, cuando fue publicada ("Efecto Ártico” ¿Pequeña Glaciación antes del 2020?) por  EcoPortal de la Argentina y por la Unidad de Comunicaciones e Información Pública del Programa de las Naciones Unidas para el Medio Ambiente- PNUMA- en México.
El “Efecto Ártico” es la denominación al fenómeno del deshielo ártico como consecuencia del calentamiento global sostenido, que afecta el equilibrio térmico del Ártico, el cual  tiende a ser restituido  con ciclos de inviernos extremos.
La hipótesis inicialmente citada, sostiene que las llamadas "Pequeñas Glaciaciones” tienen un elemento en común “un calentamiento global sostenido” de 35 a 40 años crea las condiciones mínimas para su inicio”, destacando como característica que entre mas cálidos sean los años del citado calentamiento, mas intensos y extremos serán sus inviernos, por lo cual  los inviernos del 2012 al 2017 serán gradualmente extremos.
Según la Organización Meteorológica Mundial (OMM) el actual calentamiento global se inició 1.976 cuando se elevó a un ritmo tres veces mayor de lo previsto y el decenio 1998-2007 fue el más cálido desde 1850.
Según la NASA el Calentamiento Global afecta dos veces más las áreas Occidentales del Océano Ártico, que a otras regiones del planeta.
El año 2014 ha sido confirmado como el más cálido para la Tierra desde 1880, por la NASA y la Administración Nacional Oceánica y Atmosférica (NOAA).
 
Por lo anteriormente expuesto, el actual invierno 2014-2015 debe de ser el de mayor intensidad y de las temperaturas mas extremas en por lo menos los últimos 30 años, en especial en algunas regiones del Atlántico Norte (Este de Norteamérica y Europa Occidental) por la incidencia del deshielo ártico sobre la referida región.

El “Efecto Ártico” sostiene que los veranos de los años muy cálidos tienden a extenderse hasta el otoño y los extremos inviernos pueden prolongarse hasta la primavera, lo cual será de mayor intensidad a finales del ciclo 2014-2017.
El “Calentamiento Global Sostenido” cumple este año 39 años, el mas largo periodo cálido desde la Edad Media, en que se produjo un ciclo similar de calentamiento conocido como “Optimo Climático”, el cual fue abruptamente interrumpido por un periodo de bajas temperaturas (del siglo XIV hasta 1850) denominado como  “La Pequeña Glaciación”.
Un breve ciclo de Calentamiento Global Sostenido (de 40 años) y un Mínimo Solar en el año 2020, estaría creando las condiciones mínimas que podría llevar a una “Pequeña Glaciación”.
El Histórico deshielo ártico en el año 2007-2008 afectó el termostato del planeta.
El Ártico es como el termostato del planeta: activa la circulación de las corrientes oceánicas y contribuye  a la distribución del calor entre el Ártico y los trópicos. Un estudio del Centro Nacional de Investigación Atmosférica en Boulder, Colorado demostró que las temperaturas del Ártico, en el verano de las últimas décadas han sido las más altas en  dos mil años.
Según el Centro Nacional de Datos sobre el Hielo y Nieve de la Universidad de Colorado en Boulder, el Ártico perdió 2.500.000 Km2 de hielo permanente debido al derretimiento, la mitad 1.200.000 K2, entre febrero de 2007 y febrero de 2008".
El Albedo es parte de la radiación solar reflejada por una superficie: la nieve y el hielo refleja el 90% y el color oscuro absorbe el 90%., el color del océano ártico es oscuro.
Imaginemos un gran espejo de 2.500.000 Km2 del tamaño del Mar Mediterráneo, que reflejaba el 90% del calor en el Ártico se diluyó y ahora absorbe calor en verano 24 horas al día de mayo a julio, aportando una extrema humedad que se convierte en excepcionales lluvias de primavera a otoño  y extremas nevadas en invierno.
Al aumentar el  caudal de agua dulce sobre el océano Ártico y en la región septentrional del Atlántico como consecuencia del deshielo de los glaciales y de la lluvia extrema (la cual aumenta el caudal de  los ríos que desembocan en la región) estos pierden salinidad, lo cual facilita su congelación y crea las condiciones mínimas para el próximo extremo invierno.
Un ciclo de inviernos árticos repotenciados por un Mínimo Solar a partir del 2020 podrían llevar a una “Pequeña Glaciación”.
El 19 de mayo del 2014 en el taller de clima espacial del Space Weather Prediction Center, de la NOAA, en Boulder, Colorado, científicos demostraron  que el actual Máximo Solar número 24, el cual se  inició el 4/01/2008/es uno de los más débiles de los 23 ciclos solares (de 11 años) documentados desde el año  1755.
Al concluir el actual Máximo Solar se invierte la polaridad del Sol y se inician los ciclos de Mínimos Solares a partir del año 2020.
La baja actividad solar con pocas manchas solares esta asociada con períodos de inviernos extremos que llevan a ciclos de enfriamiento en el hemisferio norte del planeta como el ocurrido entre 1645 y 1715, el cual es conocido como “Mínimo de Maunder” o La Pequeña Edad de Hielo. 
De acuerdo a modelos climáticos un Sol menos activo, implica una mayor presencia de rayos cósmicos que provocan la formación de nubes bajas, lo cual disminuye la entrada de la radiación solar, favoreciendo una disminución de la temperatura y posibilitando un enfriamiento del planeta.
Expertos en el tema vinculan la similitud del próximo mínimo solar con el “Mínimo de Maunder” en una entrevista publicada por el diario BBC de Londres (¿Se quedó dormido el Sol? Rebecca Morelle  /18/01/2014).
Según la doctora Lucie Green, del laboratorio de ciencia espacial de la University College London, de Londres, “Existen indicios muy fuertes de que ahora el Sol está actuando de la misma forma que cuando ocurrió en el mínimo de Maunder".
Y de Mike Lockwood, profesor de física ambiental espacial, de la Universidad de Reading, Reading, (Berkshire, Inglaterra) “el Sol esté cada vez menos activo: Un análisis del núcleo de hielo, que registra un largo periodo de actividad solar, sugiere que esta disminución de la actividad es la más rápida que se ha visto en 10.000 años”.
El deshielo ártico y el  Mínimo Solar una  vía  a la “Pequeña Glaciación”
Un estudio publicado el 6 Mayo del 2012 en la revista Nature Geoscience realizado por un equipo de científicos europeos del Centro Alemán de Investigación en Geociencias (GFZ), demostró que un mínimo solar ocasiono un enfriamiento brusco(menos de una década) en  Europa Occidental hace 2.800 años, con  afectación de patrones de viento y aumento de la humedad.
Un informe del Instituto Real de los Países Bajos para la Investigación Marina (4/04/2011), demostró que el deshielo ártico había aumentado el contenido de agua dulce del Ártico en un 20% desde la década de 1990, en cerca de 8.400 kms3, equivalente a toda el agua en el lago Michigan y el Lago Huron juntos, o al doble del volumen de agua del lago Victoria, el más grande de África.
Hasta el presente el agua dulce acumulada en el Ártico, no se ha desplazado sobre el Atlántico, debido a que el patrón de viento no ha variado significativamente, de ocurrir la citada variación, el desplazamiento afectaría la deriva de la cálida Corriente del Golfo (corriente del Atlántico Norte) y la densidad de la fría Corriente de Labrador, lo que llevaría a un periodo de inviernos árticos y con ello al inicio de una “Pequeña Glaciación”, en el Hemisferio Norte.
Es probable que el Mínimo Solar,  pueda incidir con sus bajas temperaturas y altere el “patrón de viento” en la región ártica y con ello desplazar sobre el Atlántico el agua dulce acumulada.
La termosfera aumenta la temperatura durante los "máximos solares", y la disminuye durante los  "mínimos solares".
Según la NASA entre el año 2008–2009, las manchas solares prácticamente desaparecieron y  se produjo la contracción más pronunciada de la termosfera, de dos a tres veces mayor que lo que usualmente ocurre con una baja actividad solar, fue causada en parte por el exceso de dióxido de carbono, el cual al llegar a la referida capa, funciona como un refrigerante extrayendo calor a través de la radiación infrarroja.
De acuerdo a Scripps Institution of Oceanography los niveles de dióxido de carbono medidos en la cima del Mauna Loa en Hawái de diciembre de 2014 a principios de enero de 2015, estuvieron sobre  los 400 ppm.
El experto Bob Ward, director de comunicaciones del Instituto Grantham de Investigación sobre el Cambio Climático y el Medio Ambiente de la Escuela de Londres de Economía y Ciencias Políticas ,aseguro que a última vez en que los niveles de CO2 se mantuvieron de forma estable por encima de 400 ppm fue hace tres millones de años.
De acuerdo a las evidencias científicas expuestas en un mínimo solar de un año (2008-2009) se redujo de dos a tres veces la termosfera.
¿Con  un mínimo solar de 11 años, en cuantas veces  se reduciría la termosfera con una Atmosfera cargada con mas 400 ppm de CO2 y como se afectaría la temperatura del planeta?

Erik Quiroga Ambientalista, 
Promotor de la creación del Día Internacional de la Preservación de la Capa de Ozono, aprobado por la Asamblea General de las Naciones Unidas (Resolución 49/114 del 23/01/95) promovido el 16 de septiembre.          

1/9/16

Gulf Stream is slowing down faster than ever, scientists say

 THE INDEPENDENT
Steve Connor@SteveAConnor .

The Gulf Stream that helps to keep Britain from freezing over in winter is slowing down faster now than at any time in the past millennium according to a study suggesting that major changes are taking place to the ocean currents of the North Atlantic.
Scientists believe that the huge volumes of freshwater flowing into the North Atlantic from the rapidly melting ice cap of Greenland have slowed down the ocean “engine” that drives the Gulf Stream from the Caribbean towards north-west Europe, bringing heat equivalent to the output of a million power stations.

However, the researchers believe that Britain is still likely to become warmer due to climate change providing the Gulf Stream does not come to a complete halt – although they remain unsure how likely this is.
Calculations suggest that over the 20th century the North Atlantic meridional overturning circulation – the northward flow of warm surface water and the southward flow of deep, cold water – has slowed by between 15 and 20 per cent, said Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.
 There is more than a 99 per cent probability that this slowdown is unique over the period we looked at since 900 AD. We conclude that the slowdown many have described is in fact already underway and it is outside of any natural variation,” Professor Rahmstorf said.The scientists calculated that some 8,000 cubic kilometres of freshwater has flowed from Greenland into the Atlantic between 1900 and 1970, and this rose significantly to 13,000 cubic kilometres between 1970 and 2000.
Freshwater is lighter than salty water which means that it tends to float on the surface of the ocean and in doing so disturbs the normal sinking of dense, cold saltwater to the ocean floor, which is the main driver of the Atlantic circulation.

In a study published in the journal Nature Climate Change, Professor Rahmstorf and colleagues point out that maps of global surface temperatures have consistently indicated an overall warming trend around the world, except for the region of the North Atlantic south of Greenland. 
“It is conspicuous that one specific area of the North Atlantic has been cooling in the past hundred years while the rest of the world heats up,” said Professor Rahmstorf, who added that previous research had indicated that a slowdown in ocean currents may be the explanation.
“Now we have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970,” he said.
 The study used proxy measurements of the Atlantic currents, using ice cores, tree rings, coral growth and ocean and lake sediments, to estimate regional temperature variations and so assess how the Gulf Stream has changed over the past 1,000 years.

Jason Box of the Geological Survey of Denmark and Greenland, who helped to calculate the amount of freshwater flowing into the Atlantic from melting ice caps, said that the slowdown can be linked to man-made climate change.
“Now freshwater coming off the Greenland ice sheet is likely disturbing the circulation. So the human-caused mass loss of the Greenland ice sheet appears to be slowing down the Atlantic overturning, and this effect might increase if temperatures are allowed to rise further,” Dr Box said.
Michael Mann of Pennsylvania State University said: “Common climate models are underestimating the change we’re facing, wither because the Atlantic overturning is too stable in the models or because they don’t properly account for Greenland ice melt, or both.”

22/1/16

Abrupt Climate Change


UNION OF CONCERNED SCIENTIST
2 Brattle Square, Cambridge

Two high-profile events in 2004 put the issue of "abrupt climate change" squarely in the public eye. The first was a February 2004 Fortune Magazine article that broke the news of a report prepared for the Pentagon on abrupt climate change and its implications for U.S. national security. The Pentagon report describes a scenario in which human-caused global warming leads to a near-term collapse of the ocean's thermohaline circulation, which brings warm surface waters from the tropics to the North Atlantic, warming parts of Western Europe. The authors propose dramatic impacts, including rapid cooling in Europe, greatly diminished rainfall in many important agricultural and urban centers and consequent disruptions in food supply and water supply with enormous geopolitical and security implications.
The second was the May 2004 release of The Day After Tomorrow a 20th Century Fox blockbuster disaster movie with a similar premise. With a dashing paleoclimatologist as the action hero, The Day After Tomorrow depicts a world careening toward an ice age over a few weeks' time. Here too, the culprit is the warming-induced shutdown of the thermohaline circulation.
The authors of the Pentagon report and the producers of The Day After Tomorrowcaution readers and viewers against treating these extreme scenarios as serious possibilities. The Pentagon report intentionally considers the worst possible scenario, one that stretches the boundary of scientific plausibility. The Day After Tomorrow leaps beyond that boundary to unleash a collection of climate catastrophes intended to thrill audiences and showcase the latest special effects. Yet underlying even these extreme scenarios are the sober facts of human-caused global warming and the real opportunities to minimize climate change by reducing emissions of heat-trapping gases.
UCS views the publicity generated by these events as an opportunity to help the public and decision makers better understand what we know about the causes, consequences and solutions to climate change. Toward that end, we provide the following answers to some frequently asked questions.

Can what happens in The Day After Tomorrowhappen in real life?

No. The dramatic, virtually instantaneous and widespread cooling envisioned in the film is fiction. But like all good science fiction, the film is premised on several important scientific facts. We know with great certainty that Earth is already warming, largely because as we burn fossil fuels and clear forests we are releasing carbon dioxide and other heat-trapping gases in the atmosphere. This warming is expected to continue in the coming decades, accompanied by changes in rainfall patterns and rising sea levels. The possibility of an abrupt shift in the climate system is only one feature of a changing climate that is expected to become more erratic, with extreme weather events like droughts, torrential rainfall, and extreme heat becoming more common. We can slow down global warming and reduce the likelihood of future abrupt climate changes by reducing our emissions of heat-trapping gases.

What is "abrupt climate change?"

The term "abrupt climate change" describes changes in climate that occur over the span of years to decades, compared to the human-caused changes in climate that are occurring over the time span of decades to centuries. From ice cores, ocean sediments, tree rings, and other records of Earth's past climate, scientists have found that changes in climate have occurred quickly in the past—over the course of a decade. An example of an abrupt climate change event is the Younger Dryas (~12,000 years ago), a period of abrupt cooling that interrupted a general warming trend as Earth emerged from the last Ice Age. During the Younger Dryas period, average summertime temperatures in New England cooled by about 5-7°F (3-4°C). This and other abrupt events have been linked to changes in an ocean circulation pattern known as thermohaline circulation.

How might abrupt climate change affect people?

While the scenarios depicted in the Day After Tomorrow and the Pentagon report are extreme, changes in climate, including possible abrupt climate changes, will have serious consequences for people's lives and livelihoods. As Earth warms, higher temperatures and more common extreme heat conditions will affect human health, energy demand, water supply and demand, and agriculture. Rising sea levels will impact coastal communities as flooding happens more often and damage from coastal storms becomes more severe. Some regions will become much drier, while others will become much wetter, affecting agriculture, water supply, and the spread of diseases. Many of these impacts will be most severe in developing countries, where scarce resources and limited technological capacity will limit options for coping with the consequences of climate change.

Can we avoid abrupt climate change?

Yes. While abrupt climate change is not a certainty, human-caused climate change makes abrupt events more likely. What is certain is that human-caused climate change is already under way, and is expected to continue over the next century as a result of our emissions of carbon dioxide and other heat-trapping gases to the atmosphere. Levels of carbon dioxide in the atmosphere are higher today than they have been for more than 400,000 years. Earth's surface temperature has increased measurably over the past 100 years, and 10 of the warmest years on record have occurred since 1990. This warming has caused changes in rainfall—some regions have become wetter while others have become drier—and droughts and severe rainfall events have become more common. By making choices now to reduce our emissions of heat-trapping gases, we can slow the rate of global warming and reduce the likelihood of unexpected climate changes.

How can global warming make things cooler?

As we rapidly increase Earth's average temperature, some regions, such as high latitudes, will experience greater warming than others, such as the tropics. As warming alters ocean and atmosphere circulation patterns, some regions could even experience cooling. Much of Western Europe is now warmed by ocean circulation as well as the atmosphere. Heat is transported to the region by a global ocean circulation pattern variably known as thermohaline circulation, the North Atlantic heat pump, or the "Great Ocean Conveyor Belt." This "heat pump" pulls warm salty water northward from the tropics into the North Atlantic, where heat is released, warming air temperatures over Europe.
As Earth warms, melting of ice caps and glaciers, increased precipitation and other inflows of fresh water to the North Atlantic Ocean may weaken or shut down thermohaline circulation. This change in ocean circulation could disrupt the transfer of heat northward from the tropics, resulting in cooling in the North Atlantic region. Regional cooling of as much as 14-29°F (8-16°C) has been seen in the past climate record. However, any regional cooling would be superimposed on the global warming that is already underway. Contrary to the "Day After Tomorrow" dramatization, abrupt climate change will not result in an ice age, because the cooling effects are regional and Earth is currently in an interglacial, or warm, period.

What is thermohaline circulation?


Thermohaline circulation is a global ocean circulation pattern that distributes water and heat both vertically, through the water column, and horizontally across the globe. As cold, salty water sinks at high latitudes, it pulls warmer water from lower latitudes to replace it. Water that sinks in the North Atlantic flows down to the southern hemisphere, skirts the Antarctic continent, where it is joined by more sinking water, and then crosses south of the Indian Ocean to enter the Pacific Ocean basin. There, the cold deep water rises to the surface, where heat from the tropical sun warms the water at the ocean's surface and drives evaporation, leaving behind saltier water. This warm, salty water flows northward to join the Gulf Stream, traveling up the Eastern coast of the United States and across the Atlantic Ocean into the North Atlantic region. There, heat is released to the atmosphere, warming parts of Western Europe. Once this warm, salty water reaches the North Atlantic and releases its heat, it again becomes very cold and dense, and sinks to the deep ocean.

6/1/16

Predicen una nueva Edad de Hielo para el año 2030


ABC

josé manuel nieves - Madrid - 18/07/2015 a las 00:00:01h. - Act. a las 03:31:47h.Guardado en: Ciencia
La noticia ha causado impacto entre climatólogos de todo el mundo. Y no es para menos. Un grupo internacional de investigadores, liderado por V. Zharkova, de la Univesidad de Northumbria, acaba de revelar, durante elEncuentro Nacional de Astronomía en Llandudno, en Gales, que estamos a punto de experimentar una nueva «Pequeña Edad de Hielo» similar a la que congeló una buena parte del mundo durante el siglo XVII y principios del XVIII. Será entre 2030 y 2040.
Como es sabido, el campo magnético del Sol varía a lo largo del tiempo. Y estas variaciones magnéticas en la ardiente atmósfera solar tienen unainfluencia directa en la radiación electromagnética que emite el astro rey, así como en la intensidad de sus flujos de plasma y en el número de manchas en su superficie. La variación en la cantidad de manchas solares tiene una estructura cíclica, con máximos que se producen cada once años y que tienen efectos concretos sobre el medioambiente de la Tierra. Esos efectos pueden medirse observando la presencia de ciertos isótopos (como el carbono 14 o el berilio 10) en glaciares o en los árboles.
Pero existen numerosos ciclos diferentes que se repiten una y otra vez, condiferentes periodos y propiedades, aunque los mejor conocidos son los de once y noventa años. El primero se manifiesta con una reducción periódica de manchas sobre la superficie solar. Y su variante de 90 años se asocia con la reducción periódica en el número de manchas en determinados ciclos de once años.
En el siglo XVII se produjo un prolongado periodo de calma, llamado «elMínimo de Maunder», que se extendió desde 1645 a 1700 y durante el cual las manchas solares prácticamente desaparecieron por completo. Durante este periodo, en efecto, apenas se contabilizaron unas 50 manchas solares en lugar de las cerca de 50.000 habituales. El análisis de la radiación solar, además, ha demostrado que sus máximos y mínimos coinciden casi siempre con los máximos y mínimos en cuanto al número de manchas.
Ahora, en un amplio estudio publicado en tres artículos diferentes, los investigadores han analizado el campo magnético de fondo de todo el disco solar durante tres ciclos completos de actividad (del 21 al 23), aplicando el denominado «análisis de componentes principales», que permite reducir la dimensión de los datos y el ruido estadístico para identificar solo las ondas que contribuyen en mayor medida a los datos de observación. El método podría compararse a la descomposición de la luz blanca por medio de un prisma, para detectar por separado las frecuencias de los diversos colores del espectro luminoso.
Como resultado, los investigadores lograron desarrollar un nuevo método de análisis, que les ayudó a descubrir que las ondas magnéticas se generan en el Sol por pares, y que el par principal basta para dar cuenta del 40% de la variación de los datos. Por lo tanto, se puede considerar al par principal de ondas como responsable de las variaciones del campo dipolar del Sol, que cambia su polaridad de polo a polo en cada ciclo de actividad de once años.
Utilizando su nuevo método de análisis, los científicos describieron la evolución de estas dos ondas y calcularon la curva de variación de las manchas solares (principal indicador de la actividad solar). Lo primero que hicieron fue predecir la actividad magnética del sol en el ciclo 24 (en el que estamos actualmente, desde 2008), y sus datos coincidieron en un 97% con las observaciones directas.
Animados por este éxito, los autores de la investigación decidieron extender la predicción a los dos ciclos siguientes (el 25 y el 26) y descubrieron que el par principal de ondas provocará en ese periodo un número de manchas muy escaso. Lo que llevará a una fuerte disminución de la actividad solarhacia 2030 ó 2040, comparable a las condiciones que existieron durante el Mínimo de Maunder en el siglo XVII.
Esta reducción de la actividad implica una disminución de la radiación solar de 3W por metro cuadrado, más del doble de lo habitual, lo que llevará a unrecrudecimiento invernal extremoy a veranos muy fríos. «Muchos estudios han mostrado que el Mínimo de Maunder coincidió con la fase más fría del enfriamiento global (en el siglo XVII), hasta el punto de que se la conoce como 'Pequeña Edad de Hielo' –afirma Helen Popova, física de la Universidad Estatal Lomonosov de Moscú–. Durante ese periodo se sufrieron inviernos muy fríos en Europa y Norte América. Durante el Mínimo de Maunder el agua de ríos como el Támesis o el Danubio se congeló, el Moscova se cubría de hielo cada seis meses, la nieve cubría las llanuras todo el año y Groenlandiaestaba cubierta de glaciares». Helen Popova es la investigadora que desarrolló el modelo matemático que ha permitido predecir la evolución de la actividad magnética del Sol.

Una atmósfera terrestre más fría

Si se produce en la actividad solar una reducción similar a la registrada durante el Mínimo de Maunder, también la atmósfera terrestre se enfriará. Según Popova, si las actuales teorías sobre el impacto de la actividad solar en el clima terrestre son ciertas, entonces el próximo mínimo de 2030 traerá un enfriamiento significativo, muy similar al ocurrido durante el siglo XVII.
Sin embargo, solo durante los próximos entre 5 y 15 años será posible tener una certeza absoluta sobre lo acertado de estas predicciones.
«Dado que nuestro futuro mínimo tendrá una duración de al menos tres ciclos solares, que es de unos 30 años, es posible que la disminución de la temperatura no sea tan drástica como durante el Mínimo de Maunder –explica Helen Popova–. Pero debemos examinar los datos con detalle. Estamos en estrecho contacto con climatólogos de varios países y seguiremos trabajando en ello».
La idea de que la actividad solar afecta al clima en la Tierra apareció hace ya mucho tiempo. Se sabe, por ejemplo, que basta una ligera variación de un 1% en la actividad solar para causar cambios medibles en la distribución de temperaturas y del flujo de aire en todo el planeta. Los rayos ultravioletatienen efectos fotoquímicos, que llevan a la formación de ozono en la atmósfera, a una altura de 30 ó 40 km. Y el flujo de rayos ultravioleta aumenta considerablemente cuando se produce una llamarada solar. El ozono, que absorbe los rayos del sol lo suficientemente bien, se calienta como consecuencia de este aumento de radiación y afecta a las corrientes de aireen las capas bajas de la atmósfera y, en consecuencia, al clima.
También la emisión de partículas cargadas aumenta con la actividad solar. Y esas partículas alcanzan la Tierra y se mueven en complejas trayectorias, causando auroras, tormentas geomagnéticas y problemas en las comunicaciones por radio.