Evidence from past suggests climate trends could yield 20-foot sea-level rise

University of Florida News: When past temperatures were similar to or slightly higher than the present global average, sea levels rose at least 20 feet, suggesting a similar outcome could be in store if current climate trends continue. Findings published in the journal Science showed that the seas rose in response to melting ice sheets in Greenland and Antarctica, said lead author Andrea Dutton, a University of Florida geochemist.

“This evidence leads us to conclude that the polar ice sheets are out of equilibrium with the present climate,” she said.

Dutton and an international team of scientists assessed evidence of higher sea levels during several periods to understand how polar ice sheets respond to warming. Combining computer models and observations from the geologic record, they found that during past periods with average temperatures 1 to 3 °C (1.8 to 5.4 °F) warmer than preindustrial levels, sea level peaked at least 20 feet higher than today.

“As the planet warms, the poles warm even faster, raising important questions about how ice sheets in Greenland and Antarctica will respond,” she said. “While this amount of sea-level rise will not happen overnight, it is sobering to realize how sensitive the polar ice sheets are to temperatures that we are on path to reach within decades.”

The researchers concluded that sea levels rose 20 to 30 feet higher than present about 125,000 years ago, when global average temperature was 1 °C higher than preindustrial levels (similar to today’s average). Sea level peaked somewhere between 20 and 40 feet above present during an earlier warm period about 400,000 years ago, when global average temperatures are less certain, but estimated to be about 1 to 2 °C warmer than the preindustrial average....

NOAA image of the Ross Ice Shelf in Antarctica

Evidence from warm past confirms recent IPCC estimates of climate sensitivity

A press release from the University of Southampton: New evidence showing the level of atmospheric CO2 millions of years ago supports recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC).

A multinational research team, led by scientists at the University of Southampton, has analysed new records showing the CO2 content of the Earth’s atmosphere between 2.3 to 3.3 million years ago, over the Pliocene.

During the Pliocene, the Earth was around 2ºC warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years. By studying the relationship between CO2 levels and climate change during a warmer period in Earth’s history, the scientists have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as ‘climate sensitivity’.

The findings, which have been published in Nature, also show how climate sensitivity can vary over the long term. “Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming,” says Southampton’s Dr Gavin Foster, co-author of the study.

“Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions.”...

Fossils from the Pliocene, shot by H. Zell, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Study tracks global sea-levels over the last five ice ages

A press release from the University of Southampton: Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study. An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.

The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.

Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: “The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.

“Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century.”

Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change. He says: “For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat.”

“This happened within 400 years for 68 per cent of all 120 cases considered, and within 1100 years for 95 per cent. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries.”

Professor Rohling speculates that there may be an important lesson for our future: “Man-made warming spans 150 years already and studies have documented clear increases in mass-loss from the Antarctic and Greenland ice sheets. Once under way, this response may be irreversible for many centuries to come.”

NASA image of an iceberg calving from the Petermann Glacier in Greenland, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license 

Can fossils reveal how to reverse biodiversity loss?

Environmental News Network via Click Green: Many native species have vanished from tropical islands because of human impact, but University of Florida scientists have discovered how fossils can be used to restore lost biodiversity.

The key lies in organic materials found in fossil bones, which contain evidence for how ancient ecosystems functioned, according to a new study published in the September issue of the Journal of Herpetology.

Pre-human island ecosystems provide vital clues for saving endangered island species and re-establishing native species, said lead author Alex Hastings, who conducted work for the study as graduate student at the Florida Museum of Natural History and UF department of geological sciences.

"Our work is particularly relevant to endangered species that are currently living in marginal environments," said Hastings, currently a postdoctoral researcher at Martin Luther University Halle-Wittenberg. "A better understanding of species’ natural roles in ecosystems untouched by people might improve their prospects for survival."…

Barracudasauroides panxianensis Stage : Anisian from 247.2 million years ago until ~242 million years ago. Shot by Didier Descouens, Wikimedia Commons, under the Creative Commons 3.0 license

No ‘permanent El Niño,’ scientists say — and the tropics may get even hotter

Eric Gershon in the Yale News: New research by Yale University scientists challenges a long-standing paradigm for temperature variability in the Pacific Ocean, casting doubt on the existence of a past period of “permanent” El Niño-like conditions and suggesting that the tropics could grow markedly hotter.

“There’s good news and bad news about future global warming,” said Mark Pagani, professor of geology and geophysics at Yale and an author of the research, published April 4 in the journal Science. “The good news is that global warming does not drive the Pacific Ocean into a permanent El Niño-like condition with all the other regional climate impacts that come with that. The bad news is that the tropics will warm as we continue to add greenhouse gases to the atmosphere — and the recent past was probably much warmer than generally assumed.”

Modern El Niño conditions are characterized by unusually warm surface water in the eastern equatorial Pacific, and a very low overall equatorial Pacific temperature gradient. The quasi-periodic phenomenon’s effects on global weather patterns can be dramatic, including extreme rainfall in some places (Texas, for example) and drought elsewhere (Indonesia and Australia).

A conventional view holds that sea surface temperatures in the warmest part of the equatorial Pacific — the vast western “warm pool” — remained relatively constant for millions of years. Given that ocean temperatures elsewhere rose during this time, the warm pool’s stable temperature implied a tropical ocean “thermostat” or temperature control mechanism, Pagani said.

But in a new reconstruction of ancient Pacific sea surface temperatures covering 12 million years, Pagani and Yale doctoral candidate Yi Ge Zhang found that Pacific warm pool temperatures were notably higher 12 million years ago than previously thought — as much as 4°C warmer. Their results indicate that all parts of the Pacific warmed during past periods of global warming, suggesting greater variability of ancient ocean temperatures and the absence of any tropical temperature control mechanism or  “permanent El Niño-like” conditions....

Ruins at Orongo on Easter Island, shot by TravelingOtter, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license 

UCLA study yields more accurate data on thousands of years of climate change

UCLA Newsroom: Using a cutting-edge research technique, UCLA researchers have reconstructed the temperature history of a region that plays a major role in determining climate around the world.  The findings, published online Feb. 27 in the journal Nature Geoscience, will help inform scientists about the processes influencing global warming in the western tropical Pacific Ocean.

The study analyzes how much temperatures have increased in the region near Indonesia, and how ocean temperatures affect nearby tropical glaciers in Papua New Guinea and Borneo. Researchers also evaluated the accuracy of existing climate model predictions for that region. The findings illustrate that the region is very sensitive to climate change and that it has warmed considerably over the last 20,000 years, since the last ice age.

The team chose the specific area examined in the study because it is Earth's warmest open ocean region and a primary source of heat and water vapor to the atmosphere. As a result, temperature changes there can influence climate not just regionally, but globally.

"The tropical Pacific ocean-atmosphere system has been called a sleeping dragon because of how it can influence climate elsewhere," said lead author Aradhna Tripati, a UCLA assistant professor in the departments of Earth, planetary and
space sciences, and atmospheric and oceanic sciences.

...As part of the study, Tripati and her colleagues also investigated what sets the past and present height of glaciers in the tropics, and why they have been retreating. To accurately estimate the height of tropical glaciers and average temperatures at altitude in this region, they found that atmospheric mixing, through a process known as entrainment, needs to be factored in.

"We found that the large amount of ocean warming goes a long way to explaining why glaciers have retreated so much," said Tripati, a faculty member in the College of Letters and Science and a member of UCLA's Institute of the Environment and Sustainability. "Throughout the region, they have retreated by close to a kilometer since the last ice age, and are predicted to disappear in the next one to three decades. Previously understanding this large-scale glacial retreat has been a puzzle. Our results help resolve this problem."...

A NASA image of the Grasberg (Freeport) copper mine pit is in the foreground, and remnants of Indonesia's Puncak Jaya glaciers behind

Recent decades likely wettest in four millennia in Tibet

A press release from the University of East Anglia: Recent decades may have been the wettest in 3,500 years in North East Tibet – according to climate researchers at the University of East Anglia (UK) and the Chinese Academy of Sciences (Lanzhou, China). Researchers looked at 3,500-year-long tree ring records from North East Tibet to estimate annual precipitation. They found that recent decades have likely been the wettest on record in this semi-arid region.

The precipitation records have been reconstructed using sub-fossil, archaeological and living juniper tree samples from the north-eastern Tibetan Plateau. They reveal a trend towards wider growth rings, implying moister growing conditions – with the last 50 years seeing increasing amounts of rainfall. Notable historical dry periods occurred in the 4th Century BC and in the second half of the 15th Century AD.

Dr Tim Osborn from UEA’s Climatic Research Unit said: “Our collaboration with scientists from China has been very fruitful, leading to what is currently the longest tree-ring-width record in the cold and arid north-eastern Tibetan Plateau. Not only is the record very long, it is based on samples from more than 1000 trees, some of which have an individual lifespan of more than 2000 years. These are among the longest-lived trees in the world.”

Not only are these trees long-lived, but they are useful for understanding how climate has changed. The widths of the tree rings show a close correspondence with observations from rain gauges over the last 55 years, such that tree rings in wetter years tend to be wider than tree rings in drier years.

Dr Osborn said: “The most recent few decades have, on average, the widest rings in the 3,500-year record which suggests that this may have been the wettest period, perhaps associated with global warming during the last century. Indeed, over the last two thousand years when the Northern Hemisphere is warm it appears to be wetter in the Mountains of North East Tibet. This suggests that any further large-scale warming might be associated with even greater rainfall in this region – though we note that other factors could also have contributed to the increased ring widths.”....

Flooding near an airport in Tibet, shot by ignat, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Unstable Atlantic deep ocean circulation under future climate conditions

AlphaGalileo via University of Bergen: A new study looking at past climate change, asks if these changes in the future will be spasmodic and abrupt rather than a more gradual increase in the temperature.

Today, deep waters formed in the northern North Atlantic fill approximately half of the deep ocean globally. In the process, this impacts on the circum-Atlantic climate, regional sea level, and soak up much of the excess atmospheric carbon dioxide from industrialisation — helping to moderate the effects of global warming. Changes in this circulation mode are considered a potential tipping point in future climate change that could have widespread and long-lasting impacts including on regional sea level, the intensity and pacing of Sahel droughts, and the pattern and rate of ocean acidification and CO2 sequestration.

Until now, this pattern of circulation has been considered relatively stable during warm climate states such as those projected for the end of the century. A new study led by researchers from the Bjerknes Centre of Climate Research at the University of Bergen (UiB) and Uni Research in Norway, suggests that Atlantic deep water formation may be much more fragile than previously realised.

...“Our study demonstrates that deep water formation can be disrupted by the freshening of the regional surface water, which might happen due to enhanced precipitation and glacier melting under future climate change scenarios,” says Yair Rosenthal, a co-author on the paper.

...Many models have actually predicted a slow and gradual decline in North Atlantic circulation over the next century. However, different models offer widely different scenarios for what will happen in the future. While the climate of the last interglacial is not exactly what will be the case in a future greenhouse world, it does share some features, including being fresher and warmer by a few degrees Celsius in the northern Atlantic....

Ocean Circulation Conveyor Belt. The ocean plays a major role in the distribution of the planet's heat through deep sea circulation. This simplified illustration shows this "conveyor belt" circulation which is driven by the difference in heat and salinity. Records of past climate suggest that there is some chance that this circulation could be altered by the changes projected in many climate models.  US federal government image

Climate history written in dust

EurekAlert via the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research: In spring 2010, the research icebreaker Polarstern returned from the South Pacific with a scientific treasure - ocean sediments from a previously almost unexplored part of the South Polar Sea. What looks like an inconspicuous sample of mud to a layman is, to geological history researchers, a valuable archive from which they can reconstruct the climatic history of the polar areas over many years of analysis. This, in turn, is of fundamental importance for understanding global climatic development. With the help of the unique sediment cores from the Southern Ocean, it is now possible to provide complete evidence of how dust has had a major influence on the natural exchange between cold and warm periods in the southern hemisphere. An international research team under the management of the Alfred Wegener Institute in Bremerhaven was able to prove that dust infiltrations there were 2 to 3 times higher during all the ice ages in the last million years than in the warm phases in climatic history.

"High large-area dust supply can have an effect on the climate for two major reasons", explained Dr. Frank Lamy, geoscientist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, about the findings. "Trace substances such as iron, which are essential for life, can be incorporated into the ocean through dust. This stimulates biological production and increases the sea's capacity to bind carbon. The result is that the greenhouse gas carbon dioxide is taken out of the atmosphere. In the atmosphere itself, dust reflects the sun's radiation and purely due to this it reduces the heat input into the Earth's system. Both effects lead to the fact that the Earth cools down."
...

...The influence of dust supply on the climate changes between ice ages and warm periods has long been suspected. Climatic researchers always found particularly high dust content containing iron when the earth was going through an ice age, both in Antarctic ice cores and in sediment cores from the Atlantic part of the Southern Ocean. However, up to now there was no data available for the Pacific section, which covers 50% of the Southern Ocean. "We can now close this central gap" is how Lamy underlines the importance of the new study. "The result is that we are now finding the same patterns in the South Pacific that we found in cores from the South Atlantic and the Antarctic ice. Therefore, the increased dust input was a phenomenon affecting the southern hemisphere during colder periods. This means that they now have to be considered differently when assessing the complex mechanisms which control natural climate changes."

..."Our investigations have now proved without a doubt that colder periods in the southern hemisphere over a period of 1 million years always and almost everywhere coincided, , with lower carbon dioxide content in the atmosphere and higher dust supply from the air. The climatic history of the Earth was, therefore, written in dust." ...

NASA image of dust over southeast Australia

The water cycle amplifies abrupt climate change

A press release from the Helmholtz Center in Potsdam: The role of the hydrological cycle during abrupt temperature changes is of prime importance for the actual impact of climate change on the continents. In a new study published in Nature Geoscience online (January 19, 2014) scientists from the University of Potsdam, Germany and the GFZ German Research Centre for Geosciences show that during the abrupt cooling at the onset of the so-called Younger Dryas period 12680 years ago changes in the water cycle were the main drivers of widespread environmental change in western Europe. The team of scientists analyzed organic remains extracted from Meerfelder maar lake sediments from the Eifel region, western Germany, to reconstruct changes in precipitation patterns in unprecedented detail. They were able to show that the intrusion of dry polar air into western Europe lead to the collapse of local ecosystems and resulted in the observed widespread environmental changes at that time.

The exact sequence of events during abrupt climate changes occurring over only a few years is one of the great unknowns in paleoclimate research. The new results presented here were obtained by using a novel method, where molecular organic remains derived from plant fossils were extracted from precisely dated annually laminated lake sediments. The ratio of the heavy Deuterium to the light Hydrogen isotopes in these biomarkers can be used to reconstruct changes in precipitation regime and moisture sources with unprecedented detail.

... Dirk Sachse, the head of the workgroup at the Institute of Earth and Environmental Sciences of the Potsdam University explains: “In our new study we can show for the first time that this change in the pathway of westerly wind systems brought dry polar air into western Europe and this was the ultimate cause for the widespread disappearance of forests in the area.”

With these new results, the group also supports the hypothesis that this change in atmospheric circulation patterns over western Europe took place 170 years after the onset of cooling, as observed in the Greenland Icecores. The authors attribute this delay to the subsequent southward expansion of sea ice in the North Atlantic following the onset of cooling. This lead to a southward shift of the polar front channeling dry polar air into western Europe. “Our results also show that abrupt climate and environmental change may not be coeval on large regional scales, but can take place with substantial regional and temporal delays” explains Prof. Achim Brauer from the GFZ German Research Centre for the Geosciences.

The results of this study, which was funded by the German Research Foundation (DFG) through its Emmy-Noether Programme and the Helmholtz Climate Initiative REKLIM, do not only show unequivocally that temperature changes can have regionally different impacts, but also that the water cycle acts as amplifier of change with potentially severe effects on continental ecosystems. ...

A view of the Meerfelder Maar, shot by Bungert55 , Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Study shows unprecedented warmth in Arctic

University of Colorado at Boulder: The heat is on, at least in the Arctic. Average summer temperatures in the Eastern Canadian Arctic during the last 100 years are higher now than during any century in the past 44,000 years and perhaps as long ago as 120,000 years, says a new University of Colorado Boulder study.

The study is the first direct evidence the present warmth in the Eastern Canadian Arctic exceeds the peak warmth there in the Early Holocene, when the amount of the sun’s energy reaching the Northern Hemisphere in summer was roughly 9 percent greater than today, said CU-Boulder geological sciences Professor Gifford Miller, study leader. The Holocene is a geological epoch that began after Earth’s last glacial period ended roughly 11,700 years ago and which continues today.

Miller and his colleagues used dead moss clumps emerging from receding ice caps on Baffin Island as tiny clocks.  At four different ice caps, radiocarbon dates show the mosses had not been exposed to the elements since at least 44,000 to 51,000 years ago.

Since radiocarbon dating is only accurate to about 50,000 years and because Earth’s geological record shows it was in a glaciation stage prior to that time, the indications are that Canadian Arctic temperatures today have not been matched or exceeded for roughly 120,000 years, Miller said.

“The key piece here is just how unprecedented the warming of Arctic Canada is,” said Miller, also a fellow at CU-Boulder’s Institute of Arctic and Alpine Research. “This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere.”

...Miller and his colleagues compiled the age distribution of 145 radiocarbon-dated plants in the highlands of Baffin Island that were exposed by ice recession during the year they were collected by the researchers. All samples collected were within 1 meter of the ice caps, which are generally receding by 2 to 3 meters a year. “The oldest radiocarbon dates were a total shock to me,” said Miller.

Located just east of Greenland, the 196,000-square-mile Baffin Island is the fifth largest island in the world.  Most of it lies above the Arctic Circle. Many of the ice caps on the highlands of Baffin Island rest on relatively flat terrain, usually frozen to their beds. “Where the ice is cold and thin, it doesn’t flow, so the ancient landscape on which they formed is preserved pretty much intact,” said Miller....

Baffin Island from the air, shot by Wes Gill, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license

Big animals crucial for soil fertility

Seed Daily: The mass extinction of large animals in the Pleistocene era caused today's dearth of soil nutrients, scientists said Sunday, and warned of further damage if modern giants like the elephant disappear.

The Pleistocene epoch, which dated from about 2.6 million to 11,700 years ago, saw large animals dubbed megafauna take over domination of the planet from extinct dinosaurs, only to die out en masse themselves.

During their peak, much of the world resembled a modern-day African savannah. South America, for example, was teeming with five-tonne ground sloths, armadillo-like glyptodonts the size of a small car, and herds of elephant-like cuvieronius and stegomastodonts.

These megafauna, animals weighing more than 44 kilograms (97 pounds), played a key role in fertilising soil far away from the areas near rivers where they fed -- ploughing the nutrients they consumed back into circulation through their dung or their decomposing bodies when they died.

Large animals ate much more and travelled further than small ones, and were mainly responsible for long-distance fertilisation, said a study published in the journal Nature Geoscience....

Comparison of the dog-sized weasel Ekorus ekakeran, of what is now Kenya, with the jackal-sized civet, Viverra leakeyi, of what is now South Africa. From the Late Miocene of Africa (C) Stanton F. Fink. Uploaded by Apokryltaros, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

East Antarctica's ice sheet not as stable as thought

Carolyn Gramling in Science Now: ...Many studies have tried to estimate how much and how rapidly the two great ice sheets covering Greenland and Antarctica might melt—and the one reassuring point has been the apparent relative stability of the eastern (and, by far, larger) half of the Antarctic Ice Sheet. Now, a new study of past melting in East Antarctica suggests that over the long haul, the "stable" ice sheet may be more vulnerable to warming than thought.

To study possible future melting of the ice sheets, many scientists look to the past. Current warm temperatures and high greenhouse gas conditions are reminiscent of the warm Pliocene Epoch that lasted from 5.3 million to 2.6 million years ago. "Early and middle Pliocene global temperatures and greenhouse gas concentrations are probably the closest analog in Earth's history to the present climate on this planet and the climate conditions we will encounter before the end of this century," says Claus-Dieter Hillenbrand, a sedimentologist at the British Antarctic Survey in Cambridge, U.K., who was not involved in the study.

Abundant studies have examined melting of the Greenland Ice Sheet and the West Antarctic Ice Sheet (WAIS)—long considered the more vulnerable portion of the continent's ice, as much of it lies below sea level, flowing seamlessly into floating ice shelves. Satellite observations reveal that the WAIS is losing mass, sped up by melting along the base of the floating portions as the oceans warm. But the East Antarctic Ice Sheet (EAIS), which lies primarily on land, has appeared considerably more stable.

Yet, data from the Pliocene tell a different story, says Carys Cook, a doctoral student at Imperial College London. Mean temperatures from the Pliocene were 2°C to 3°C warmer than today, and atmospheric carbon dioxide concentrations between 350 and 450 parts per million. Some data have also suggested that sea levels were perhaps 22 meters higher than today—and even complete melting of the WAIS and Greenland couldn't account for more than about 12 meters of that, Cook says. Melting of the EAIS would have to have contributed.

...In those sediments, the team looked for geochemical "fingerprints"—specifically, geochemical ratios of neodymium to strontium isotopes—that would help them identify the provenances, or sources, of the different layers of sediments. What they found in the Pliocene sediments was telling: They identified multiple layers containing a unique fingerprint for a large, low-lying part of East Antarctica known as the Wilkes Subglacial Basin, which is now ice-covered. For those sediments to have eroded and ended up offshore in the marine core, the basin would have had to be exposed by retreat of the ice, the team reports today in Nature Geoscience.

This does suggest that the East Antarctic Ice Sheet may not be as stable in a warm climate as some models suggest, Hillenbrand says. And, given that it indicates that the Pliocene had both ice-free warm periods and glacial periods, it's an "interesting alternative scenario" to the more extreme reconstructions that suggest either widespread melting across East Antarctica or no melting at all relative to today....

Lemaire Passage, shot by christopher* , Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license

Siberian caves warn of permafrost meltdown

AlphaGalileo via the Geological Society of London: Climate records captured in Siberian caves suggest 1.5 degrees of warming is enough to trigger thawing of permafrost, according to a paper to be given at the Geological Society of London on 27 June. Permafrost regions cover 24% of the northern hemisphere land surface, and hold an estimated 17,000 Gt of organic carbon. Thawing releases CO2 and CH4, creating positive feedback during greenhouse warming.

The researchers, led by Gideon Henderson at the University of Oxford’s Department of Earth Sciences, studied speleothem records from the caves to identify periods where temperatures were above freezing. Speleothems, such as stalactites and stalagmites, form when water seeps through cracks in cave walls, dissolving minerals which precipitate in the air filled cave.

‘Cave temperatures usually approximate the local mean annual air temperature’ says Anton Vaks, the paper’s lead author. ‘When they drop below 0 degrees, the rock above and around the cave freezes, and speleothem growth stops.’

By dating the speleothems and comparing their ages to existing climate records, it is possible to identify the degree of warming which caused the permafrost to melt. New results from Ledyanaya Lenskaya Cave, Eastern Siberia, extend previous records to one million years, and show major deposition of speleothems at around one million years and 400,000 years ago.

‘Both episodes occurred when global temperatures increased 1.5°C ± 0.5 above the pre-industrial level’ says Vaks, ‘showing that this degree of warming is a tipping point for continuous permafrost to start thawing.’ Global temperatures are currently around 0.7 degrees above pre-industrial level, with current models suggesting that a warming of 1.5°C ± 0.5 will be achieved within 10-30 years....

Siberia's Laptev Sea viewed from a NASA satellite

Tracking the earth’s mantle -- and sea level rise

Rob Enslin in Syracuse University News: From Virginia to Florida, there is a prehistoric shoreline that, in some parts, rests more than 280 feet above modern sea level. The shoreline was carved by waves more than 3 million years ago—possible evidence of a once higher sea level, triggered by ice-sheet melting. But new findings by a team of researchers, including Robert Moucha, assistant professor of Earth Sciences in The College of Arts and Sciences, reveal that the shoreline has been uplifted by more than 210 feet, meaning less ice melted than expected.

Equally compelling is the fact that the shoreline is not flat, as it should be, but is distorted, reflecting the pushing motion of the Earth’s mantle. This is big news, says Moucha, for scientists who use the coastline to predict future sea-level rise. It’s also a cautionary tale for those who rely almost exclusively on cycles of glacial advance and retreat to study sea-level changes.

“Three million years ago, the average global temperature was two to three degrees Celsius higher, while the amount of carbon dioxide in the atmosphere was comparable to that of today,” says Moucha, who contributed to a paper on the subject in the May 15 issue of Science Express. “If we can estimate the height of the sea from 3 million years ago, we can then relate it to the amount of ice sheets that melted. This period also serves as a window into what we may expect in the future.”

Moucha and his colleagues—led by David Rowley, professor of geophysical sciences at the University of Chicago—have been using computer modeling to pinpoint exactly what melted during this interglacial period, some 3 million years ago. So far, evidenced is stacked in favor of Greenland, West Antarctica and the sprawling East Antarctica ice sheet, but the new shoreline uplift implies that East Antarctica may have melted some or not at all. “It’s less than previous estimates had implied,” says Rowley, the article’s lead author.

Moucha’s findings show that the jagged shoreline may have been caused by the interplay between the Earth’s surface and its mantle—a process known as dynamic topography. Advanced modeling suggests that the shoreline, referred to as the Orangeburg Scarp, may have shifted as much as 196 feet. Modeling also accounts for other effects, such as the buildup of offshore sediments and glacial retreats.

“Dynamic topography is a very important contributor to Earth’s surface evolution,” says Rowley. “With this work, we can demonstrate that even small-scale features, long considered outside the realm of mantle influence, are reflective of mantle contributions.”...

The East Coast shoreline, also known as the Orangeburg Scarp, as it may have appeared 3 million years ago. From the Syracuse University website

Scientists explore roots of future tropical rainfall

Space Daily via SPX: How will rainfall patterns across the tropical Indian and Pacific regions change in a future warming world? Climate models generally suggest that the tropics as a whole will get wetter, but the models don't always agree on where rainfall patterns will shift in particular regions within the tropics.

...Pedro DiNezio of the University of Hawaii and Jessica Tierney of Woods Hole Oceanographic Institution investigated preserved geological clues (called "proxies") of rainfall patterns during a time when the planet went into opposite gear and cooled dramatically in the last ice age. Land clues included charcoal from fires, and evidence of more sand dune activity and desiccated lakes, all indicating drier conditions, and evidence for higher lake levels and more pollen, indicating wetter conditions.

They also looked at records of seafloor sediments containing preserved shells of dead marine organisms; the shells contain higher or lower levels of a heavier isotope of oxygen, depending on the relative salinity of surface waters when the organisms were alive (less salty waters indicate more rainfall over the ocean).

...They then compared this evidence with results from 12 different mathematical climate models that simulate Earth's climate, which incorporate basic laws of physics, chemistry, and fluid dynamics surrounding air-sea-land-ice interactions. ...Their results surprised them: Only one model, developed by the Hadley Centre for Climate Prediction and Research in the England, reproduced the rainfall patterns they found from the geological evidence....

..."The good news is, the Hadley model combined with the geological evidence show a pathway to improve our ability to simulate and predict tropical rainfall in the future," Tierney said....

Rainfall from Cyclone Gonu in 2005, via NASA

Ice-free arctic may be in our future

UMassAmherst Office of News & Media Relations: Analyses of the longest sediment core ever collected on land in the Arctic, recently completed by an international team led by Julie Brigham-Grette of the University of Massachusetts Amherst, provide “absolutely new knowledge” of Arctic climate from 2.2 to 3.6 million years ago and show that with estimated atmospheric carbon dioxide (CO2) similar to today’s levels, the Arctic was very warm, with no ice sheets.

“While existing geologic records from the Arctic contain important hints about this time period, what we are presenting is the most continuous archive of information about past climate change from the entire Arctic borderlands. As if reading a detective novel, we can go back in time and reconstruct how the Arctic evolved with only a few pages missing here and there,” says Brigham-Grette.

Results of analyses that provide “an exceptional window into environmental dynamics” never before possible were published this week in Science and have “major implications for understanding the pacing and context of how the Arctic transitioned from a forested landscape without ice sheets to the ice- and snow-covered land we know today,” she adds.

Their data come from analyzing sediment cores collected in the winter of 2009 from under ice-covered Lake El’gygytgyn, the oldest deep lake in the northeast Russian Arctic. “Lake E” was formed 3.6 million years ago when a huge meteorite hit the Earth and blasted out an 11-mile (18 km) wide crater. It has been collecting sediment layers ever since. Luckily for geoscientists, it lies in one of the few Arctic areas not eroded by continental glaciers, so a thick, continuous sediment record was left remarkably undisturbed. Cores from Lake E reach back in geologic time nearly 30 times farther than Greenland ice cores that cover the past 140,000 years.

“One of our major findings is that the Arctic was very warm in the Pliocene [~ 5.3 to 2.6 million years ago] when others have suggestedatmospheric CO2 was very much like levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier models,” the authors state....

NASA image showing the location of Lake El'gygytgyn

Circulation changes in a warmer ocean

AlphaGalileo: Circulation changes in a warmer ocean In a new study, scientists suggest that the pattern of ocean circulation was radically altered in the past when climates were warmer. Ancient warm periods offer useful insights into potential future warming and its impacts.  The mid-Pliocene, ~3 million years ago, was a relatively recent period of global warmth that is often considered as an analog for our future.

During this warm period, unusually warm surface conditions existed in the North Atlantic, which has often been simply explained by the intensification of the existing pattern of ocean circulation. However, reproducing these changes with climate models has eluded researchers for more than a decade—suggesting either that there was something wrong with the long-standing explanation or with the models used to predict the behavior of warmer oceans.

A team of Bergen scientists reevaluated the existing observations and used the Norwegian Earth System model (NorESM) to carry out simulations to better understand ocean circulation during the warm mid-Pliocene.

They illustrated that the largest changes occurred in the deep Southern Ocean, but not in the North Atlantic, indicating that the existing explanation was not adequate. They found that the data and simulations pointed toward an altogether different pattern of ocean circulation, with Antarctic waters playing a stronger role due to faster renewal of the deeper water masses in the Southern Ocean during the mid-Pliocene. This alternative explanation provided a solution to the long standing discrepancy between reconstructions of ocean circulation at the time and available model simulations.

The team also addressed the unusual warmth in the North Atlantic during the warm mid-Pliocene.  The observed high latitude warmth was shown not to require the intensification of todays ocean circulation and the transport of ocean heat to the north, rather it was a direct response to changes in insolation and atmospheric carbon dioxide levels at the time. The study highlights just how differently ocean circulation was when the planet was warmer and carbon dioxide levels were high...

Simulated changes in sea surface temperature (oC, contours) with comparison to reconstructed changes (circles) in the North Atlantic.

Tree-ring data show history, pattern to droughts

University of Arkansas Newswire: Dendrochronologists have shown that tree-ring data produce a remarkably accurate history of droughts and other climate changes. Combined with reliable drought indices and historical descriptions of climate conditions, dendrochronology – the technique of dating events and environmental change by relying on characteristic patterns of tree-ring growth – can provide a climate perspective on important events such as large-scale human migration and even the rise and fall of entire civilizations.

A research team, including University of Arkansas Distinguished Professor and dendrochronologist David Stahle and Ewing Research Professor Edward Cook of Columbia University, used more than 1,400 climate-sensitive tree-ring chronologies from multiple tree species across North America to reconstruct the Palmer drought severity index (PDSI), a widely used soil moisture index. Stahle presented his research Friday, Feb. 15, in a symposium on “U.S. Climate and Weather Extremes:  Past, Present, and Future,” during the American Association for the Advancement of Science annual meeting in Boston. He also participated in a panel discussion with other climate experts.

The Palmer drought severity index is based on instrumental temperature and precipitation data dating back to 1895. Stahle and his colleagues inserted the index between fixed points on a grid covering most of North America. Their tree-ring reconstructions cover the same geographic area but extend back to 800 A.D. Stahle wanted to examine the reconstructed indices to test the accuracy of the records and to see if there were any patterns related to drought and other climate changes. The findings were dramatic.

“Comparisons of reconstructed PDSI with instrumentally measured PDSI during the 20th century document the remarkable accuracy with which the tree-ring data reproduce the spatial pattern and intensity of observed drought at annual and decadal time scales, including the Dust Bowl drought of the 1930s,” Stahle said.

The data also confirmed historical descriptions of climate conditions prior to the modern era of instrumentation for weather and climate measurements...

Tree rings shot by Lokilech, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

US study says El Nino, climate change link fuzzy

Space Daily via AFP: The frequency and volatility of El Nino, a weather pattern that hammers the tropical Pacific Ocean every five years or so, does not seem linked to climate change, said US research released Thursday. The study involved scientists measuring the monthly growth of ancient coral fossils found on two tropical Pacific islands to determine what, if any, impact the warming climate had on the weather phenomenon.

By reconstructing temperatures and precipitation over the millenniums, the study compared it to the frequency and intensity of El Nino and found that the latter had indeed become more intense and frequent in the 20th century.

But although the increase was statistically significant and could be linked to climate change, the long historic record provided by the coral fossils allowed the researchers to determine that the El Nino Southern Oscillation, or ENSO, has also had large natural variations in past centuries. Thus, it is not clear that changes seen in recent decades can be linked to climate change caused by rising levels of carbon dioxide, the researchers said.

"The level of ENSO variability we see in the 20th century is not unprecedented," said climatologist Professor Kim Cobb, from the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. "But the 20th century does stand out, statistically, as being higher than the fossil coral baseline," she added....

Fossilized coral stones, shot by Irwan Holmes, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license