Science Says: No Ice in the North Pole by 2016

ORIGINAL: The Guardian

By Alison Fairbrother

September 20, 2012

Record low Arctic Ice will impact climate change, sea level rise, and food security.

Is that the saddest yellow line you've ever seen? (Photo: NASA/Reuters)

The summer ice cap in the Arctic will be gone within four years, a leading expert has predicted, calling the imminent melt a “global disaster.” 

“Climate change is no longer something we can aim to do something about in a few decades’ time, and that we must not only urgently reduce CO2 emissions but must urgently examine other ways of slowing global warming, such as the various geoengineering ideas that have been put forward,” Dr. Peter Wadhams, professor of ocean physics at the University of Cambridge, told the Guardian. 

Wadhams has collected years of data on the thickness of sea ice from submarines that motor under Arctic ice. The cause of the melt, he says plainly, is global warming.

The Arctic will be ice-free by 2015 or 2016, Wadhams told the Guardian, and “the final collapse towards that state is now happening.” 

MORE: Dear Mr. President: Why on Earth Are You Allowing Shell's Arctic Drilling?

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Earlier estimates predicted that summer ice in the Arctic would last another 50 years. But the accelerating rate of ice melt has surprised climatologists. 

On September 16, the National Snow and Ice Data Center (NSIDC) announced that the sea ice cover had reached a record low of 1.32 million square miles—the smallest amount of Arctic ice ever documented, and about half the average recorded between 1979 and 2000.

“We are now in uncharted territory,” NSIDC director Mark Serreze wrote in a press release. “While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur.”

The center had previously announced a record low of 1.58 million square miles on August 26, only to see that record shattered a few weeks later.

“The six lowest September ice extents have all been in the past six years,” Serezze told NBC News. “I think that’s quite remarkable.” Sezerre said he believes summer ice will have melted completely by 2030—a slightly longer time frame than posited by Dr. Wadhams. 

But they seem to agree that the impacts of the great Arctic melt will be drastic—and should serve as a sober warning to policymakers.

Warmer Arctic conditions will likely release huge amounts of methane, a greenhouse gas currently trapped under permafrost. When released, as much as four billion tons of methane will pollute the atmosphere, further contributing to global warming.

The melting at the top of the world will also cause sea level rise, threatening the security and health of coastal communities.

As the Arctic heats up, many fish species will travel north, seeking colder ocean temperatures. This, in turn, will alter the availability of food sources.

Not everyone is recoiling in horror at the idea of an ice-free Arctic. Some see the melting as a chance to enrich magnates and investors in shipping and oil companies.

Descubren un bosque bajo el Ártico

ORIGINAL: Más Verde Digital

Es un bosque en medio del desierto helado”. Así lo describen, en un comunicado, los científicos que han descubierto, en una expedición de la NASA, que el Océano Ártico se está tiñendo de verde por la proliferación de plantas marinas microscópicas, que son esenciales para la vida en otros mares, pero que no habían sobrevivido hasta ahora en un ecosistema tan frío.

El calentamiento global está, según el trabajo publicado en ‘Science’ detrás de un fenómeno que hasta ahora no se había detectado en toda su amplitud.

La expedición ICESCAPE (siglas de Impactos del Clima en los Ecosistemas y la Química del Ártico) exploró las aguas de los mares de Beaufort y Chukchi, en Alaska, a bordo de un rompehielos estadounidense. “Hemos observado una masiva expansión del fitoplancton entre 800 centímetros y 1,3 metros en la capa helada del primer año en el mar Chukchi”, aseguran los autores.

Esa capa se extiende en más de 100 kilómetros, un fenómeno que no había sido observado hasta ahora. Los cambios en el Ártico ya habían sido detectados por imágenes de satélite de la NASA. La expedición tenía como objetivo confirmar los datos, en un lugar de difícil acceso desde tierra.

Hasta ahora se pensaba que estas plantas que tiñen de verde el agua y son la base de la cadena alimenticia marina, sólo crecían después de que el hielo del mar se retiraba, lo que ocurre en verano. El problema, dice el biólogo Sam Laney, del Woods Hole Oceanographic Institution, está en que, igual que un aguacero hace florecer el desierto, la acumulación de agua de deshielo en cortos periodos de tiempo en el Ártico tienen importantes efectos sobre el ecosistema.

Según sus análisis, al adelgazarse el hielo, la luz solar llega a las aguas que hay bajo la capa helada sobre el mar, lo que permite que la planta se desarrolle. “Si alguien me hubiera preguntado si veríamos flores bajo el hielo, les habría dicho que no era posible”, reconoce Kevin Arrigo, de la Universidad de Stanford y líder de la expedición. “Ha sido una completa sorpresa”, ha asegurado.

El fitoplancton, además, tuvo un crecimiento extremadamente activo, llegando a doblar su cantidad en un solo día, cuando las flores, en aguas abiertas, tardan dos o tres. Es más, los investigadores estiman que estas tasas pueden llegar a multiplicar por 10 las tasas de crecimiento de las plantas en aguas abiertas.

Como el fitoplancton, a su vez, consume grandes cantidades de dióxido de carbono, los científicos tendrán que evaluar, más adelante, cuánto CO2 está entrando en el Océano Ártico si resulta que estas plantas llegan a ser comunes bajo el hielo. “En este momento no sabemos si estas floraciones acaban de empezar a producirse o si es que no las hemos observado antes”, señala Arrigo, quien cree que si el hielo sigue adelgazando, al final se convertirá en un bosque sobre el mar.

Fuente: Diario El Mundo, Agencias

Carbon dioxide caused global warming at Ice Age's end, pioneering simulation shows

ORIGINAL: Oak Ridge National Laboratory (ORNL)

Groundbreaking demo proves model to predict climate's future can reproduce its past

Global temperature mirrored and generally lagged behind rising carbon dioxide during Ice Age's deglaciation, pointing to carbon dioxide as the major driver of global warming.

Climate science has an equivalent to the "what came first—the chicken or the egg?" question: What came first, greenhouse gases or global warming? A multi-institutional team led by researchers at Harvard, Oregon State University, and the University of Wisconsin used a global dataset of paleoclimate records and the Jaguar supercomputer at Oak Ridge National Laboratory (ORNL) to find the answer (spoiler alert: carbon dioxide drives warming). The results, published in the April 5 issue of Nature, analyze 15,000 years of climate history. Scientists hope amassing knowledge of the causes of natural global climate change will aid understanding of human-caused climate change.

"We constructed the first-ever record of global temperature spanning the end of the last ice age based on 80 proxy temperature records from around the world," said Jeremy Shakun, a National Oceanic and Atmospheric Administration (NOAA) Climate and Global Change postdoctoral fellow at Harvard and Columbia Universities and first author of the paper. "It's no small task to get at global mean temperature. Even for studies of the present day you need lots of locations, quality-controlled data, careful statistics. For the past 21,000 years, it's even harder. But because the data set is large enough, these proxy data provide a reasonable estimate of global mean temperature."

Proxy records from around the world—derived from ice cores and ocean and lake sediments -- provide estimates of local surface temperature throughout history, and carbon-14 dating indicates when those temperatures occurred. For example, water molecules harboring the oxygen-18 isotope rain out faster than those containing oxygen-16 as an air mass cools, so the ratio of these isotopes in glacial ice layers tells scientists how cold it was when the snow fell. Likewise, the amount of magnesium incorporated into the shells of marine plankton depends on the temperature of the water they live in, and these shells get preserved on the seafloor when they die. The authors combined these local temperature records to produce a reconstruction of global mean temperature. Additionally, samples of ancient atmosphere are trapped as air bubbles in glaciers, providing a direct measure of carbon dioxide levels through time that could be compared to the global temperature record.

Being the first to reconstruct global mean temperatures throughout this time interval allowed the researchers to show what many suspected but none could yet prove: "This is the first paper to definitively show the role carbon dioxide played in helping to end the last ice age," said Shakun, who co-wrote the paper with Peter Clark of Oregon State University. "We found that global temperature mirrored and generally lagged behind rising carbon dioxide during the last deglaciation, which points to carbon dioxide as the major driver of global warming." Prior results based on Antarctic ice cores had indicated that local temperatures in Antarctica started warming before carbon dioxide began rising, which implied that carbon dioxide was a feedback to some other leading driver of warming. The delay of global temperature behind carbon dioxide found in this study, however, shows that the ice-core perspective does not apply to the globe as a whole and instead suggests that carbon dioxide was the primary driver of worldwide warming.

Nature article:http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html

While the geologic record showed a remarkable correlation between carbon dioxide and global temperature, the researchers also turned to state-of-the-art model simulations to further pin down the direction of causation suggested by the temperature lag. Jaguar recently ran approximately 14 million processor hours to simulate the most recent 21,000 years of Earth's climate. Feng He of the University of Wisconsin, Madison, a postdoctoral researcher, plugged the main forcings driving global climate over this time interval into an Intergovernmental Panel on Climate Change (IPCC)-class model called the Community Climate System Model version 3, a global climate model that couples interactions between atmosphere, oceans, lands, and sea ice. The climate science community developed the model with support from the National Science Foundation (NSF), Department of Energy (DOE), and National Aeronautics and Space Administration (NASA) and used many codes developed by university researchers.

"Our model results are the first IPCC-class Coupled General Circulation Model (CGCM) simulation of such a long duration (15,000 years)," said He, who conducted the modeling with Zhengyu Liu of the University of Wisconsin-Madison and Bette Otto-Bliesner of the National Center for Atmospheric Research (NCAR). "This is of particular significance to the climate community because it shows, for the first time, that at least one of the CGCMs used to predict future climate is capable of reproducing both the timing and amplitude of climate evolution seen in the past under realistic climate forcing."

The group ran simulations that used 4.7 million processor hours in 2009, 6.6. million in 2010, and 2.5 million in 2011. The Innovative and Novel Computational Impact on Theory and Experiment program, jointly managed by leadership computing facilities at Argonne and Oak Ridge National Laboratories, awarded the allocations.

Shaun Marcott and Alan Mix of Oregon State University analyzed data, and Andreas Schmittner, also of Oregon State, interpreted links between ocean currents and carbon dioxide. Edouard Bard of Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement provided data and expertise about radiocarbon calibration.

NSF supported this research through its Paleoclimate Program for the Paleovar Project and NCAR. The researchers used resources of the Oak Ridge Leadership Computing Facility, located in the National Center for Computational Sciences at ORNL, which is supported by DOE's Office of Science. The paleoclimate community generated the proxy data sets and provided unpublished results of the DATED Project on retreat history of the Eurasian ice sheets. The NOAA NGDC and PANGAEA databases were also essential to this work.

Plot twist: the 'bipolar seesaw'

As the dominant theory goes, the variation of Earth's orbit around the sun is responsible for the growth and deterioration of glaciers because it changes insolation, or solar radiation reaching and warming an area. About 21,000 years ago the orbit of the Earth was slightly predisposed to warmer summers in the Northern Hemisphere, and the planet experienced a general warming.

Next comes a plot twist. Geologic data show that about 19,000 years ago, Northern Hemisphere glaciers began to melt, and sea levels rose. Melting glaciers dumped so much freshwater into the ocean that it slowed a system of currents that transports heat throughout the world. Called the Atlantic Meridional Overturning Circulation (AMOC), this ocean conveyor belt is particularly important in the Atlantic where it flows northward across the equator, stealing Southern Hemisphere heat and exporting it to the Northern Hemisphere. The AMOC then sinks in the North Atlantic and returns southward in the deep ocean. A large pulse of glacial meltwater, however, can place a freshwater lid over the North Atlantic and halt this sinking, backing up the entire conveyor belt.

The simulation showed weakening of the AMOC due to the increase in glacial melt beginning about 19,000 years ago, which decreased ocean heat transport, keeping heat in the Southern Hemisphere and cooling the Northern Hemisphere. Other studies suggest this southern warming caused sea ice to retreat and shifted winds around the Southern Ocean, uncorking carbon dioxide that had previously been stored in the deep ocean and venting it to the atmosphere around 17,500 years ago. This rise in carbon dioxide then initiated worldwide warming.

The seesawing of heat between the hemispheres due to the AMOC shutdown explains why Southern Hemisphere warming led the rise in carbon dioxide while Northern Hemisphere temperatures lagged behind and reconciles these patterns with the key role played by carbon dioxide in driving global mean warming. "Differences in the deglacial temperature evolution of the Northern and Southern Hemispheres can largely be explained by variations in the strength of the Atlantic Meridional Overturning Circulation," said He.

Before the team's groundbreaking efforts, researchers could only simulate single time slices of Earth's climate. Just as multiple images are stitched together to make an animation, speedy petascale supercomputers, capable of executing a quadrillion calculations each second, enable stitching together of multiple time slices to produce a continuous simulation. Liu, Otto-Bliesner, and He's group was the first to continuously capture climate from 21,000 years ago to the present day so that scientists could compare the relationship of carbon dioxide and global mean temperature over time. The Nature article covers events up to about 6,000 years ago. The group has since extended the simulation through the present day.

"Climate model output housed at Oak Ridge is currently in the hundreds of terabytes [trillion bytes] and will soon exceed a petabyte, so you need a large facility just to accommodate the large data output," said He. "Right now the climate model output is a top consumer of data storage in Oak Ridge. Also, [continuous simulations] definitely cannot be performed at other sites because the system needs to be quite consistent. This simulation has been run continuously for more than 3 years. Each simulation [step] depends on what happened earlier."

To understand the relevance of the study's finding to today, it is worth considering that carbon dioxide concentrations rose from 185 parts per million (ppm) to 260 ppm over the approximately 10,000 years during which the last ice age ended. In just the past two centuries, human activity has increased concentrations by about the same amount, reaching a carbon dioxide concentration of 392 ppm in 2011—higher than at any time in at least the last 800,000 years.

The work builds on a continuous simulation by Liu and colleagues of Earth's climate between 21,000 and 14,000 years ago, reported in a 2009 Science article detailing the first continuous simulation of climate change during Earth's most recent period of natural global warming. Using ORNL's Cray X1E supercomputer named Phoenix and the even faster Cray XT system called Jaguar, the scientists used nearly a million processor hours in 2008 to run one-third of their simulation, from 21,000 years ago (the most recent glacial maximum) to 14,000 years ago (the most recent major period of natural global warming). The effort validated the ability to simulate large climate changes in the past and is critical for assessing future projections of changes, such as the fate of ocean circulation in the face of continued glacial melting in Greenland and Antarctica.— Dawn Levy, April 4, 2012

Submerged Forests off the coast of Wales: a Climate Change Snapshot

ORIGINAL: SkepticalScience
by John Mason

7 April 2012 

Sea-level rise over the past 10,000 years is recorded in Cardigan Bay, off the western seaboard of Wales, UK. Peat-beds complete with the remains of trees are today exposed over low tide along several of the Bay's beaches. Incredibly, a new exposure of peat has recently yielded human footprints, made some 3000 years or more ago by the people who witnessed the final stages of the drowning of the land.

The deglaciation that followed the Last Glacial Maximum, twenty thousand years ago, was accompanied by a global sea-level rise that averaged out at some 120 metres. Around the British Isles, there are many areas covered by shallow seas, 10-20 metres in depth, and Cardigan Bay, off the west-facing coast of Wales, is one of them. Sailing due west from the local coastal ports such as Aberystwyth and Aberdyfi, it is a good ten nautical miles before the 20m submarine contour is reached. The sea-bed is a sandy table-land, divided by several great ridges of gravel and boulders - the Sarnau (Welsh for Roads) - that mark the lateral moraines of the valley-glaciers that flowed out westward to join the Irish Sea Ice-Sheet.

above: view across Cardigan Bay to the Snowdonia mountains, with one of the Sarnau, Sarn Cynfelyn, in the foreground. It extends out beneath the sea as a steep-sided reef for over six nautical miles. Photo: author.

The process of post-glacial sea-level rise has been well-charted, and with respect to this corner of the world, the inundation of the land to form much of Cardigan Bay was within the last 10,000 years. We have additional local evidence for this timescale: peat samples, dredged from the seabed not far from Aberystwyth, at a depth of 18.5 metres, yielded a radiocarbon date of 8740 +/- 100 years before present (Haynes et al, 1977). It should be noted in passing that this part of the UK is regarded as having been essentially neutral with respect to post-glacial isostatic rebound: to the north, where the main ice-sheets were formerly located, the land rose whilst to the south, which was mostly ice-free, the land sank.

above: the post-glacial rise in sea-level, adapted from Fleming et al (1998), with dates relevant to this article annotated in red.

8740 years: let's just place that date in context. The Younger Dryas had come and gone (12,900-11,800 years BP), and the Mesolithic was about halfway through. The people who lived in the region were gradually turning from full-time hunter-gatherers to the combination of these with agriculture, something which by the Neolithic was developing various degrees of sophistication. By then, the rate of sea-level rise had slowed, but it continued to advance throughout the Neolithic and the following Bronze Age, and there is impressive evidence from that process right here on the Welsh coast.

above: timeline annotated with the period during which Cardigan Bay was inundated.

So-called Submerged Forests are known from various parts of the world, but the one at Borth, on the Cardigan Bay Coast of Wales, is a particularly fine example. Every winter, after storms have scoured away parts of its extensive sands, large areas of peat appear, littered with fallen tree-trunks and with stumps in growth position. Although it is sometimes referred to as the "Fossil Forest", the wood is not fossilised as such: it looks and feels just like what one might expect waterworn and waterlogged wood to look and feel like. The peat is hard and compact: walking on its surface barely leaves a mark.

above: part of the Submerged Forest at Borth. Photo: author.

The basal peat, upon which the tree-stumps are situated, is around 6,500 years old. Above it, where erosion has not removed it, there lies a layer of bluish-grey clay and, at the south end of the beach, atop the clay is a second, thinner peat. The succession records the transition from forest to salt-marsh, between 6,500 and 3,000 years ago, which is late Mesolithic through to mid Bronze Age. It is thought that, originally, the coastline, with its shingle storm-beach and dunes, was over a kilometre to the west (seawards): during this period, the storm-beach advanced towards the land and its immediate hinterland became salt-marsh: the trees became waterlogged with brackish water and died. The retreat of the coast would likely have continued were it not for the establishment of the fishing-village of Borth and various sea-defences, the most recent of which is just nearing completion. Local people living here are constantly reminded of sea-level rise when they look out across the beach at low tide and see the trees emerging from the waves.

The Submerged Forest has recently been in the news. In February 2012, retired geology lecturer Dr Denis Bates, of Aberystwyth, noticed that a new area of ancient peat had become visible along the southernmost part of the beach. Taking a closer look, he discovered that the peat contained scatters of burnt stone - an archaeological feature typical of Bronze Age sites. Burnt stone consists of sharp, angular fragments of bleached-looking rock produced by heating large pebbles in fires and then immersing them in water: it was the instant cooling that shattered them. Why they did this is not clear: one theory is that it was a means of heating-up the water whilst some archaeologists have connected the practise with sweat-lodges, as in the Native American tradition.

Dr Martin Bates, Denis' son, is an archaeologist based at the University of Wales, Lampeter, and was therefore quickly on hand to undertake a detailed investigation of this find. Despite the peat and clay beds spanning an important period of human activity in the area, they have to date yielded few remains: an Aurochs skeleton was discovered many years ago and a small number of flint and bone implements have been recorded over the years. But when surveying commenced, the site proved to be of even greater interest, as upon the surface of the upper peat layer, and impacting into the clay below, the surveyors discovered footprints. There were the circular depressions made by the hooves of cattle, sheep and goats and, incredibly, human prints. It appears that the adults were foot-clad, but one print was found that belonged to a child aged approximately four years, which showed the impressions of bare toes. I visited the site over low tide a few days ago: standing next to such impressions, my heavy rigger-boots hardly left a mark: back when the prints were made this would have been squelchy marsh that you could go up to your knees in if unlucky.

above: photographed whilst still underwater, a human footprint in now hard and compact peat at the Submerged Forest, Borth. Photo: author.

Interestingly, coastal West Wales has its very own Flood Legend, which goes as follows:

Cantre'r Gwaelod (also known as Cantref Gwaelod or Cantref y Gwaelod) translates into English as the Lowland Hundred. It is the legendary sunken kingdom that is said to have long ago occupied a tract of fertile land in what is now Cardigan Bay. Cantre'r Gwaelod's capital was Caer Wyddno, seat of the ruler Gwyddno Garanhir. The land is usually described as being defended from the sea by a dyke, complete with sluice-gates, managed by one Seithennin, who, it was said, was fond of his drink. One dark and stormy night, the gates were neglected during drunken festivities and as the tide rose, so the sea swept in, ruining the land.

above: lost landscapes? A map of the UK, Ireland and N France ten thousand years ago, at the start of the Mesolithic, when sea levels, though rising, had not yet reached their full post-glacial extent. The brown areas are lands that have since been lost. Redrawn from Lambeck, 1995 (PDF).

Mere folklore, yes, but it is often wondered locally whether the legend recalls stories handed down over many generations, via the oral tradition, of lands that produced good hunting and gathering, but which by the start of the Neolithic had largely been lost to the advancing sea. The generations of people who followed-on from those who left the footprints would certainly have witnessed the environmental changes that led to the loss of the forests described above: they would have walked through what had become salt-marsh beneath dead and dying oaks and pines. They would have seen environmental change as starkly as anyone.

So what is in store for this small corner of the planet in the coming decades? According to Vermeer and Rahmsdorf (2009), the worst-case scenario would be a rise of 190cm by 2100. Using Alex Tingle's handy plotter, this is what a rise of 2m would look like:

Add caption

And a rise of 6m, which would occur if parts of both the Greenland and West Antarctica ice-sheets continued to melt, would look like this:

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Borth and Aberdyfi would be overwhelmed and even my hometown some distance inland would be affected: the fertile agricultural lands along the Dyfi flood-plain would be replaced by the relatively poor grazing offered by salt-marsh and another legend of flood would be born. Being rather fond of these places and the communities that live in them, I would personally prefer an outcome that did not involve such inundation. Future generations have just as much right to enjoy them as I do at present. It is such considerations that come to mind when people ask me why I blog.

Confirming carbon's climate effects

ORIGINAL: EurekAlert

Researcher helps paint the fullest picture yet of how increases in CO2 helped end the ice age

Harvard scientists are helping to paint the fullest picture yet of how a handful of factors, particularly world-wide increases in atmospheric carbon dioxide, combined to end the last ice age approximately 20,000 to 10,000 years ago.

As described in a paper published April 5 in Nature, researchers compiled ice and sedimentary core samples collected from dozens of locations around the world, and found evidence that while changes in Earth's orbit may have touched off a warming trend, increases in CO2 played a far more important role in pushing the planet out of the ice age.

"Orbital changes are the pacemaker. They're the trigger, but they don't get you too far," lead author Jeremy Shakun, a visiting postdoctoral fellow in Earth and Planetary Science Shakun, said. "Our study shows that CO2 was a much more important factor, and was really driving worldwide warming during the last deglaciation."

Though scientists have known for many years, based on studies of Antarctic ice cores, that deglaciations over the last million years and spikes in CO2 were connected, establishing a clear cause-and-effect relationship between CO2 and global warming from the geologic record has remained difficult, Shakun said. In fact, when studied closely, the ice-core data indicate that CO2 levels rose after temperatures were already on the increase, a finding that has often been used by global warming skeptics to bolster claims that greenhouse gases do not contribute to climate change.

Many climate scientists have addressed the criticism and shown that the lag between temperature and CO2 increases means that greenhouse gases were an amplifier, rather than trigger, of past climate change, but Shakun and his colleagues saw a larger problem – while CO2 measurements taken from air bubbles in the ice cores reflect levels throughout the global atmosphere, temperatures recorded in the ice only reflect local Antarctic conditions.

To get a more accurate picture of the relationship between global temperature and CO2, they synthesized dozens of core samples – 80 in all – collected from around the world.

"We have ice cores from Greenland, people have cored the sea floor all around the world, they've cored lakes on the continents, and they have worked out temperature histories for all these sites," Shakun said. "Putting all of these records together into a reconstruction of global temperature shows a beautiful correlation with rising CO2 at the end of the ice age. Even more interesting, while CO2 trails Antarctic warming, it actually precedes global temperature change, which is what you would expect if CO2 is causing the warming".

"The previous science clearly said that CO2 had something to do with warming," Shakun added. "It has gone up and down in tandem with the ice ages, so it is clearly involved. If it was an amplifier, the question was how big of an amplifier? Does it explain a lot of climate change, or was it a small piece, and other factors were more important? I think this research really points a strong finger at the idea that CO2 was a major player."

Armed with that evidence, Shakun and colleagues were able to sketch out how a series of factors aligned that eventually led to a worldwide warming trend and the end of the ice age.

Most scientists now believe, Shakun said, that the first domino wasn't an increase in greenhouse gases, but a gradual change in Earth's orbit. That orbital change resulted in more sunlight hitting the northern hemisphere. As the ice sheets over North America and Europe melted, millions of gallons of fresh water flooded into the North Atlantic and disruped the cyclical flow of ocean currents.

"Ocean circulation works like a global conveyor belt," Shakun said. "The reason it's important for climate is because it's moving heat around. If you look at it today, the northern hemisphere is on average, a couple degrees warmer than the south, and that's partly because the ocean is pulling heat northward as it flows across the equator in the Atlantic".

"But if you turn the conveyor belt off, it's going to warm the south because you're no longer stealing that heat away. Warming the southern hemisphere, in turn, shifts the winds and melts back sea ice that had formed a cap, trapping carbon in the deep ocean."

As more and more CO2 enters the atmosphere, Shakun said, the global warming trend continues, "and pretty soon you're headed out of an ice age."

While the research strengthens the link between CO2 and the Ice Ages, Shakun believes it also reinforces the importance of addressing CO2-driven climate change in our own time.

"I don't think this tells us anything fundamentally new about global warming," Shakun said. "Most scientists are not in doubt about the human-enhanced greenhouse effect – there are nearly a dozen strong pieces of evidence that it is affecting global climate. This is just one more log on the fire that confirms it."

###

Shakun's research was supported by a National Oceanic and Atmospheric Administration Climate and Global Change Fellowship and by the National Science Foundation, and conducted using resources at the Oak Ridge National Laboratory.

---

http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html

Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation

• Jeremy D. Shakun,
• Peter U. Clark,
• Feng He,
• Shaun A. Marcott,
• Alan C. Mix,
• Zhengyu Liu,
• Bette Otto-Bliesner,
• Andreas Schmittner
• & Edouard Bard

• Affiliations
• Contributions
• Corresponding author

Nature

 

484,

 

49–54

 

(05 April 2012)

 

doi:10.1038/nature10915

Received

 

16 September 2011 

Accepted

 

01 February 2012 

Published online

 

04 April 2012

The covariation of carbon dioxide (CO2) concentration and temperature in Antarctic ice-core records suggests a close link between CO2 and climate during the Pleistocene ice ages. The role and relative importance of CO2 in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO2 during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.

a, Location map. CBT, cyclization ratio of branched tetraethers; MBT, methylation index of branched tetraethers; TEX86, tetraether index of tetraethers consisting of 86 carbon atoms;   , alkenone unsat…

Las primeras plantas terrestres pueden haber sumido a la Tierra en una serie de las edades de hielo

ORIGINAL: TheGuardian

Ian Sample, corresponsal de ciencia

01 de febrero 2012

Científicos afirman que la difusión de las primeras plantas terrestres redujeron el carbono en la atmósfera y enfriaron el planeta

Plantas antiguas podrían haber disuelto rocas de silicatos liberando iones metálicos, que reaccionaron con carbono en la atmósfera. Foto: Reuters

Las primeras plantas en echar raíces en tierra firme pueden haber enfriado la Tierra lo suficiente como para provocar una serie de las edades de hielo, afirman los científicos.

Mientras que las plantas que se diseminaron en los continentes, extraían minerales de las rocas en las que se aferraban disminuían los niveles de carbono en la atmósfera, provocando que las temperaturas cayeran marcadamente, dicen los investigadores.

El escenario explica una glaciaciones desconcertantes que vieron adelantando que muestran capas de hielo previas al período Ordovíciano entre 488m y 444m años atrás. En ese momento, los continentes de la Tierra se agrupaban sobre el polo sur y se extendían hacia el norte hasta el Ecuador.

Escribiendo en la revista Nature Geoscience, un equipo dirigido por Timothy Lenton de la Universidad de Exeter describe experimentos para investigar el impacto ambiental de las primeras plantas terrestres de la Tierra. Tomaron piedras y cubrieron alguunas con musgo para imitar la vida de las plantas sencillas que florecieron en el Ordovícico, luego las incubaron durante tres meses.

Los experimentos en el Centro John Innes en Norwich revelan cómo la vida de las plantas podrían haber alterado la geoquímica lo suficiente para hacer descender la temperatura y dar paso a un período de glaciación del planeta.

A medida que las plantas crecieron, disolvieron las rocas de silicatos, como el granito, causando la liberación de iones de calcio y magnesio. Estos iones se combinan con el carbono atmosférico y cayeron en los océanos donde se precipitaron en forma de rocas carbonatadas. Este proceso sólo podría haber causado que la temperatura cayera alrededor de cinco grados centígrados.

En otro proceso, las plantas extraen el fósforo y el hierro de las rocas, pero a medida que las plantas murieron estos elementos han encontrado su camino hacia el mar. El aumento de nutrientes era probable que haya impulsado el crecimiento del plancton, criaturas microscópicas que secuestran carbono al crecer y al final lo llevan al fondo del mar cuando mueren, donde se forman la rocas.

Los científicos asumieron que el 15% de la superficie de la Tierra estaba cubierta de vida vegetal primitiva, pero incluso con una cobertura del 5% de la tierra, los efectos de enfriamiento que han sido sustanciales, dijo Lenton.

"Aunque las plantas están todavía enfriamiento el clima de la Tierra mediante la reducción de los niveles de carbono atmosférico, ésto no puede equipararse con la velocidad del cambio actual del clima inducido por el hombre", dijo Lenton. "Se necesitarían millones de años para que las plantas eliminaran las emisiones actuales de carbono de la atmósfera."

Liam Dolan, un científico en plantas de la Universidad de Oxford que trabajó con Lenton, dijo que la invasión de la tierra por las plantas fue un momento crucial en la historia del planeta que produjo enormes cambios climáticos. "Nuestro descubrimiento pone de relieve que las plantas tienen un papel central de regulación en el control del clima:. Lo hicieron ayer, que hoy en día, y seguramente en el futuro"