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The Greenland ice sheet melted much more rapidly as a result of warmer temperatures in the recent past than previously estimated, a team of international scientists has revealed. They warn that future warming could have more dramatic effects on the ice than researchers have assumed. The research is from this week's Nature and there's a news story about it over at Nature News.

This study is the latest in a series to use data from ice cores to fathom out what was going on in Greenland's climatic past. Between 9,000 and 6,000 years ago, Earth went through an unusually warm period. But puzzlingly, unlike data from many other spots in the Northern Hemisphere, measurements of isotopes in ice cores drilled from the Greenland ice sheet haven't reflected that temperature change. So models of the ice sheet's behaviour based on these data have suggested that the height of the ice sheet has remained quite stable during the past 12,000 years.

Now, new data from ice cores drilled in six different places on and around the ice sheet reveal that this unusually warm period affected the GIS too, and that in response to these temperatures — which were 2–3 °C hotter than our current temperature — it lost 150 metres in height at its centre and shrank by 200 kilometres at the edges.

Continue reading "Climate change warning from Greenland" »

Posted by Kerri Smith on September 16, 2009
Categories: Palaeoclimate | Permalink | Comments (3) | TrackBacks (0)

Some of scientists’ gravest concerns about future climate change are rooted in the past. Records studied by paleoclimatologists reveal that the more extreme possibilities for this century and beyond — temperatures soaring, ice sheets vanishing, fertile lands withering into deserts — were realized previously on Earth when atmospheric greenhouse gas levels surged. At this summer's AGU Chapman Conference on Abrupt Climate Change, researchers described this turbulent history through all manner of proxies - ice, tree rings, corals, marine and lake sediments, among others. But few talks went without a slide showing the wiggly line of a deep ice core.

Each proxy has its own merits, but ice cores offer records of climatic history whose detail and completeness are unmatched. Their data stretch back 800,000 years and are conveniently located in some of the world’s most climatically sensitive regions. Two new features on Nature Reports Climate Change pay homage to the work of scientists who, over the last few decades, have been tireless in their efforts to extract clues about the Earth’s past climate from air bubbles, isotopes and dust particles trapped in ice.

First, a timeline of deep polar cores documents in fine detail the discoveries of scientific pioneers, from the first efforts to read ice records through to today’s hunt for ice a million years old or more. Complementing this chronology of scientific discovery is an interactive map layer for Google Earth. This virtual tour takes you to the sites where polar researchers have holed up year after year, drilling thousands of metres of Greenland or Antarctic ice before hitting bedrock. In the window below, spin the globe to the pole of your choice, zoom in and click on the map points to see the drilling stations. For a full-size view and more navigation controls - plus a built-in web browser window where you can check out the timeline - download the map layer here and run it in Google Earth, which you can download here.

As I highlighted earlier on the blog, this month's issue of NRCC also features an exclusive interview with world-renowned glaciologist Lonnie Thompson. On his quest to understand how ice is changing atop the world’s mountains, Thompson has spent more spent more time above 20,000 feet than any other human being; he's currently with a team at the Quelccaya glacier in Peru, racing to bring back ice that is rapidly being lost to climate change. The American Museum of Natural History has put together a great video on his work.

Such endeavours come with scientific challenges as well as personal ones. As understanding abrupt climate change becomes increasingly crucial, ambitious plans for studying these icy environs will be ever more important.

Anna Barnett

Posted by Anna Barnett on August 03, 2009
Categories: Anna Barnett, Cryosphere, Palaeoclimate | Permalink | Comments (2) | TrackBacks (0)

In the latest salvo of the scientific debate over future sea level rise, a new report counters claims that rapidly swelling seas will soak estimates published by the UN climate planel in 2007.

A major “it’s worse than we thought” story out of March’s Copenhagen Climate Congress, for example, was that sea level could climb more than a metre by 2100 - seemingly far worse than the rise of up to 59 centimetres indicated in the 2007 report from the Intergivernmental Panel on Climate Change (IPCC). This was in fact something of a straw-man comparison, since the IPCC total explicitly excluded the impacts of accelerated glacier melt, and the new studies were attempting to add these impacts in.

But the latest study suggests that even considering glacier effects, the 2100 rise is likely to be well under a metre. A trio of researchers - Mark Siddall of Columbia University in New York, Thomas Stocker of the University of Bern (current co-chair of IPCC Working Group I) and Peter Clark of Oregon State University - used a new method that looks to the past to inform this future projection.

Continue reading "Sea level rise: not so fast" »

Posted by Anna Barnett on July 28, 2009
Categories: Climate prediction, In the News, Ocean science, Palaeoclimate | Permalink | Comments (2) | TrackBacks (0)

Some glacial periods in the Earth’s more recent geological past have been cooler and more severe than others, despite very similar greenhouse gas concentrations and orbital parameters. What is it that decouples global temperature from carbon dioxide levels and the solar heat?

Changes in ocean circulation, particularly in the climatically crucial North Atlantic region, are the most likely candidate. A paper in Nature (subscription required) now suggests that some of these changes originate more than 10,000 kilometres away in the subtropical Indian Ocean.

Edouard Bard and Rosalind Rickaby analysed an 800,000-year record of sea surface temperature and ocean productivity from an ocean sediment core retrieved off the southeastern coast of South Africa (Editor's summary). This is the region where a portion of the warm and salty water carried southwards by the Agulhas current, the Indian Ocean equivalent to the Gulf Stream, leaks into the South Atlantic. The inflow compensates for the export of cold Atlantic deep water to other ocean basins. More importantly, it fuels the Atlantic overturning circulation which carries warm tropical surface water towards the poles, and cold deep water back towards the equator.

The strength of this heat conveyor depends on the position of ocean fronts, boundaries between water masses of different temperature and salinity, which are known to intermittently shift northwards and southwards.

Bard and Rickaby suggest that the Agulhas current between Madagascar and the African coast has almost come to a halt during times when the subtropical front in the Indian Ocean migrated northwards by up to 1,000 kilometres. Isotopic data from the sediment record suggest this has happened at least twice, namely during glacial stadials around 340,000 and 420,000 years ago. The closure of the Agulhas ‘valve’ might explain why these glacial periods have been severely colder than most others before and thereafter.

Continue reading "Indian Ocean: Gatekeeper to climate extremes?" »

Posted by Anna Barnett on July 15, 2009
Categories: Ocean science, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (0) | TrackBacks (0)

A reconstruction of the Earth’s climatic history during a key hot period 55 million years ago has highlighted a yawning gap in our understanding: this period’s rise in carbon dioxide accounts for just half of its warming. Some as-yet-unidentified climate feedbacks could be at work, the scientists behind the research conclude.

The era under scrutiny is the Palaeocene-Eocene Thermal Maximum (PETM). Paleoclimatologists believe that the PETM could mimic our own future climate, because it’s thought to have kicked off with a pulse of carbon dioxide roughly equivalent to what humans are currently pumping out by burning fossil fuels. In a study published in Nature Geoscience (subscription), Richard Zeeb of the Universtiy of Hawaii and colleagues make a new, more precise estimate of the PETM’s carbon dioxide release based on ocean sediment records.

The increasing carbon levels caused ocean acidification that dissolved deep-sea carbonate compounds. By using measurements of this process along with a carbon-cycle model, the team inferred that during the period’s initial CO2 spike, no more than 3 billion tonnes of the gas was released over 5,000 years. Even before then, the planet looked like a greenhouse – it had a much warmer climate than today and about 1,000 parts per million CO2 in the atmosphere. Over the main phase of the PETM, the group estimates the CO2 level rose to 1,700 parts per million.

But according to the IPCC’s best guess at climate sensitivity, that 70% rise should have pushed up global temperatures 3.5 degrees Celsius at most. Other proxy records indicate, though, that temperatures soared by 5 to 9 degrees. In other words, the consensus climate sensitivity - the value, devilishly hard to pin down, for how much warming will result from a given greenhouse gas increase - doesn’t seem to be holding.

Continue reading "Unknown climate culprit for Palaeocene-Eocene warming" »

Posted by Anna Barnett on July 14, 2009
Categories: Anna Barnett, Climate prediction, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

At the AGU Chapman Conference last month I met up with Lonnie Thompson, the alpine glaciologist who has spent more time above 20,000 feet than any other human. Despite being interrupted by last-minute demands from Peruvian customs officials - he was squeezing me in before taking off for a new expedition in the Andes - an unphased Thompson carefully laid out the past and present-day climate change that his work has uncovered. Here's an extract:

What information can you garner from glaciers?

Glaciers are like sentinels, and they're telling us that the system is changing. The first thing we look for in the ice is radioactivity from thermonuclear bomb tests in 1962–1963 and 1951–1952. Back in 2006, we drilled three cores in the southwestern Himalayas. At 6,050 metres, where those glaciers reach their highest elevation, we found that neither of these radioactive layers was preserved. The glaciers are being decapitated. Not only are they retreating up the mountain slopes, but they are thinning from the top down.

This same scenario is playing out on Mount Kilimanjaro in Africa. When we drilled there in 2000 we found the 1951 test preserved, but not the 1962 test. We've since continued to monitor those glaciers and we know that we've lost three metres of ice since 2000. If we had waited until this year to drill, we would not have found the 1951 bomb horizon, because that has now been lost.

What does that mean for climate science?

Once a glacier melts, the history it contained is gone forever, so there's an urgency in trying to collect the records before they are lost.

The loss of tropical glaciers is very telling because they're in such sensitive places. Half of the surface of the planet lies between 30° N and 30° S. That's where the heat that drives the climate system is received. It's also where 70 per cent of the 6.7 billion people on the planet live.

What's the effect on people as these glaciers disappear?

After this meeting, we're headed to Peru to drill new ice cores at two sites. That country contains 75 per cent of the world's glaciers. Eighty per cent of its population is in the desert on the west coast, and 76 per cent of the electricity comes from hydropower, from streams that are fed by glaciers in the Andes, all of which are retreating. Those changes are impacting the ability to produce hydropower, to irrigate crops in the desert and to provide municipal water supplies.

Read the full interview here.

Anna Barnett

Image: © Thomas Nash 2000. All rights reserved.

Posted by Anna Barnett on July 09, 2009
Categories: Anna Barnett, Cryosphere, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

It's one of the biggest problems in the Earth's history: What prompted the Cambrian explosion of multi-cellular animal life? (Though calling it the 'Cambrian explosion' is a misnomer at this point; most geologists agree that life took off a bit earlier than the Cambrian 540 million years ago -- probably 50 million years or so before that boundary.)

Now, a new study in Nature [subscription] presents an intriguing explanation: It was photosynthetic life on land, beginning 850 million years ago, that allowed oxygen levels to rise in the atmsophere. Higher oxygen levels, in turn, allowed respiratory animals to get bigger. As I explain in an accompanying news story, the land life wasn't plants -- it was more likely a dense, mossy, worldwide matting.

The evidence is indirect: isotope records trapped in carbonate rocks formed in shallow seas. Some researchers are skeptical since fossil evidence is virtually non-existent. Moreover, the study will be controversial in geochemistry circles because the authors' interpretations of the isotope data is very different from another popular line of thinking, which sees radical changes in ocean chemistry closer to the Cambrian boundary as being the impetus for the animal explosion.
Image: Diego Cupolo

Eric Hand is a staff reporter in Nature's Washington Bureau.

Posted by Eric Hand on July 08, 2009
Categories: Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

Why carbon dioxide concentrations over the past 24 million years or so have never dropped below 200 parts per million, despite environmental conditions that have been favourable for CO2 drawdown by rock weathering and sedimentation, has always been a bit of a mystery.

Now scientists suggest an almost provocatively simple mechanism that might have kept the planet from cooling more severely than it actually did during past glacial climates: Changes in terrestrial vegetation stopped the weathering-driven decline in atmospheric CO2 concentrations which else would have turned Earth into a lifeless freezer.

Weathering is known to be largely controlled by vegetation. So the team, led by Mark Pagani of Yale University, describes in a paper in Nature today a negative feedback whereby limited plant growth during cold conditions slows down the rate of weathering and sedimentation, thus preventing carbon dioxide levels from dropping even further. An editor's summary of the paper is here.

This “bold and provocative” hypothesis provides an “elegant twist” on existing ideas about climate-vegetation interactions, Yves Goddéris and Yannick Donnadieu write in an accompanying News and Views article (subscription required).

But the proposed feedback mechanism raises contentious issues as well. For example, Goddéris and Donnadieu argue that in the tropics the role of vegetation cover in the climate system might not be as significant as proposed.

Quirin Schiermeier

Posted by Quirin Schiermeier on July 02, 2009
Categories: Categories, Biosphere feedbacks, Climate Science, GHG emissions, Palaeoclimate, Quirin Schiermeier, Topics | Permalink | Comments (0) | TrackBacks (0)

A never-before-seen megadrought made an appearance this morning at the last day of the AGU Chapman Conference. Paul Aharon of the University of Alabama says his latest observations are the first to suggest that drought affected the southeastern United States from about 13,000 to 11,800 years ago - during the so-called Younger Dryas cool period.

The evidence comes from the De Soto Caverns in Alabama. This cave has already offered up rich history of a non-palaeoclimatological kind: it holds a Native American burial ground and an abandoned moonshine distillery from the 1930s, when good-timing Alabamans used to shoot down the stalactites.

Continue reading "AGU Chapman Conference: Megadrought in Dixieland" »

Posted by Anna Barnett on June 19, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

At the AGU Chapman conference today, Yale archaeologist Harvey Weiss took the prize for an abrupt climate change picture worth a thousand words. Excavating an Akkadian palace in Tell Leilan, Syria, in 2006 and 2008, Weiss's team found one room with a grain storage vessel smashed on the floor. Lying next to it were a standard litre measure used for rationing grain, and the tablet on which a bureaucrat had been recording the rationing. The artifacts date from about 2190 B.C., when cities and towns of the Akkadian empire in Mesapotamia were being abandoned en masse as the region suffered crushing drought.

"This site is the Pompeii of ancient Mesapotamia," says Weiss. "They walked away."

Weiss reviewed evidence that a rapid change in storm tracks in the North Atlantic - yet to be satisfactorily explained - dried out the Tigris and Euphrates valley 4,200 years ago. And that valley wasn't alone. Around the same time, deflection of the Indian Monsoon hit the Nile with a drought, and Egypt's Old Kingdom went down. The extreme events are also mirrored in North America from New Jersey to the Yukon. In a separate talk today, glaciologist Lonnie Thompson showed a new ice core data* from Huascarán in Peru, the highest tropical mountain, with a huge spike in dust deposition around this time. The dust probably blew off an aridifying West Africa, Thompson says.

Continue reading "AGU Chapman Conference: "They walked away"" »

Posted by Anna Barnett on June 18, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Extreme Events, Palaeoclimate, Society | Permalink | Comments (0) | TrackBacks (0)

As the Earth has alternated between glacial and inter-glacial periods, the steep climatic ups and downs have gone hand in hand with changes in atmospheric carbon dioxide levels. But where was the CO2 going to and coming from? Scientists have pointed to the ocean – currently a vast sponge for the greenhouse gas.

But a talk at the AGU Chapman Conference today by palaeoclimatologist Lowell Stott of the University of Southern California suggests a radically different reservoir: pools of liquid carbon dioxide trapped in seafloor hydrothermal vents.

These pools were spotted in the mid 2000s unleashing bubbles of liquid CO2 from the Okinawa trough in the Pacific Ocean (see the video here).

The CO2 pools form when one oceanic plate buckles under another and carbonates in the sediment break down under the intense heat. Perforations around underwater volcanic vents can allow CO2 droplets to escape and bubble up to the surface, but where the seawater is cold enough it effectively freezes the CO2 into a solid, or hydrate, form that acts as a lid. NOAA has a further explanation and diagram.

Stott points out that the carbon isotope signatures in some mid-latitude ocean sediment don’t tally with the conventional view of carbon entering the ocean system via photosynthesizing algae. The chemistry of the sea-vent carbon is a much better match, he argues. What's more, unpublished work by Stott and colleagues shows that past changes in deep sea temperatures around the vents would have been sufficient to destabilize hydrate caps and thus modulate the vents' release of CO2 in time with the rising and falling atmospheric CO2 concentrations.

Continue reading "AGU Chapman: Could seafloor vents control atmospheric CO2?" »

Posted by Anna Barnett on June 17, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Ocean science, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

Today's theme at the AGU Chapman Conference on Abrupt Climate Change is that big baddie of climatic tipping points, the shutdown (and rebooting) of the Atlantic Meridional Overturning Circulation, or AMOC. Could this massive system go down again? Tom Delworth of NOAA took on that question and offered up some interesting new modelling evidence.

When running strong, AMOC carries heat from the Southern Hemisphere northward. It's thought that some of the past coolings under scrutiny here stem from slowing or stopping of this conveyor belt. AMOC's future change in response to greenhouse gas increases was recently considered in an assessment report on abrupt change by the US Climate Change Science Program, which Delworth helped author.

While some state-of-the-art models suggest the circulation could slow this century - a 25-30% decrease is the report's best estimate - not a single one forecasts another shutdown in that time. That led the US panel to evaluate AMOC shutdown as "very unlikely", in the parlance of the IPCC - meaning a less than 10% probability. The lack of support from models meant they couldn't set the likelihood any higher, says Delworth - but on the other hand, the possibility of flawed simulations kept them from setting it lower, at "extremely unlikely". But Delworth's new work validates the model results.

Continue reading "AGU Chapman: Meridional madness" »

Posted by Anna Barnett on June 16, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Climate prediction, Extreme Events, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

A scant 21,000 years ago, Columbus, Ohio, was blanketed by the Laurentide ice sheet. Today it is home to the Byrd Polar Research Centre at Ohio State University, where this morning I sat in a glacially air-conditioned lecture hall watching an animation of that sheet flickering rapidly back and forth across Columbus and the rest of the northern parts of the continent. Such strobe-light climate change from the Earth's past is the focus of the AGU Chapman Conference on Abrupt Climate Change, being held here this week.

Though it's a fairly small gathering of 150 experts, it doesn't have the annual reunion feeling of some meetings; many of the people here seem never to have met before. We've got palaeoscientists of various persuasions: they reconstruct climatic history via models, ice, sediment, or - as geochemist Henry Pollack described his work on borehole temperature records to me over hors d'oerves - by "taking the Earth's temperature through its rectum". (Jokes about giant thermometers ensued.)

The common thread is figuring out what caused abrupt changes in the past - and what that implies about the prospects for their return. Says Richard Alley, a Penn State glaciologist and IPCC author, "The IPCC reports are the most optimistic thing we can put forward, because the projections are smooth. If you look at any palaeo record, there are bumps. This meeting is all about the bumps."

One innovative study on show today applied the models behind those smooth future projections to the bumpy past record. Bette Otto-Bliesner of NCAR says her group's research is the first to feed palaeo data into an IPCC-style coupled global climate model and run it continuously for several thousand years during the last deglaciation - rather than just taking snapshots in time, as was done previously. Having given the model instructions about what the greenhouse gas levels, sea ice extent, and meltwater flows should be, they found that it beautifully reproduced the bumpy North Atlantic temperature record.

Continue reading "AGU Chapman: It's all about the bumps" »

Posted by Anna Barnett on June 15, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Climate prediction, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

In a Mexican eco park, of all places, scientists have found compelling evidence that sea-levels can rise – nah, jump – at scary rates during warm climates such as ours.

That the global sea-level can rise by almost half a metre per decade when huge glaciers melt towards the end of an ice age has already been known. But a paper in Nature today (Editor’s summary) suggests that a similar jump has occurred at the close of the sea-level ‘highstand’ during the warm period, the Eemian Interglacial.

The team, led by Paul Blanchon of the National Autonomous University of Mexico in Cancun, analyzed the age structure of exceptionally well-exposed coral reefs at Xcaret, a popular theme park on the northeast Yucatán peninsula. Because no earthquakes have occurred in the more recent geological history of the region, the peninsula is an ideal location to study sea-level behaviour.

The team found that at the end of the last interglacial many reefs were flooded and replaced by new reefs on higher ground. Age and layering of the corals indicate that a rapid 2-3 metres jump in sea-level occurred around 121,000 years ago, possibly within less than one century.

Only swift and substantial melting of Greenland and Antarctic ice sheets can explain the extreme rate at which the seal level rose to its highstand some 4-6 metres above today’s sea-level.

The implications for our warming planet are clear. As modern temperatures approach those at the height of the Eemian Interglacial, the rate of seal-level rise could soon – perhaps very soon - shift gear, from modest to catastrophic.

The spectacular break-up of the Wilkins Ice shelf off the Antarctic Peninsula is a reminder that we are getting closer to the point where things could get really nasty.

“Given the dramatic disintegration of ice shelves and discovery of rapid ice loss from both the Antarctic and Greenland ice sheets, the potential for sustained rapid ice loss and catastrophic sea-level rise in the near future is confirmed by our discovery of sea-level instability at the close of the last interglacial,” the authors conclude.

Quirin Schiermeier

Posted by Quirin Schiermeier on April 16, 2009
Categories: Ocean science, Palaeoclimate, Quirin Schiermeier, Topics | Permalink | Comments (1) | TrackBacks (0)

Two papers in Nature today shed light on the possible future behaviour of the West Antarctic ice sheet (WAIS), complete loss of which would produce a worldwide rise in sea level of around 5 metres.

The two teams - one using a high-resolution ice sheet model, the other looking at glacial records contained in seafloor sediment – independently arrive at similar conclusions: The WAIS has intermittently melted during the past five million years or so, and its oscillations follow a 40,000 year cycle in the Earth’s axial tilt. Small variations in tilt – called the obliquity of the ecliptic – result in reduced or increased amounts of sunlight reaching the poles, thus pacing the succession of ice ages and warm periods.

During the warmest interglacial phases the WAIS has in the past episodically collapsed entirely, the studies suggest (Editor's Summary) Global temperatures around 3 degrees Celsius warmer than today seem to have sufficed to initiate the transition from grounded ice to open waters in the Ross Bay, reports the team led by Tim Naish of Victoria University in Wellington, New Zealand, who analysed a sediment core recovered from beneath the Ross ice shelf by the ANDRILL programme. Model simulations suggest the transition from full glacial to intermediate state (such as today’s) to nearly ice-free conditions can proceed rapidly. In the warmest ‘super-interglacials’, such as one around 1.07 million years ago, it took only around thousand years for the WAIS to collapse, report David Pollard and Robert DeConto of Pennsylvania State University in the second study.

Image: Punchstock

Continue reading "Antarctica: Memento melting " »

Posted by Quirin Schiermeier on March 19, 2009
Categories: Cryosphere, Palaeoclimate, Quirin Schiermeier, Topics | Permalink | Comments (1) | TrackBacks (0)

Posted on behalf of Roberta Kwok

Scientists have found a new way to estimate past climate: snakes.

In case you haven't seen the media flurry, researchers have uncovered the remains of a gigantic snake in northeastern Colombia (which news outlets have described as "Super-snake", "Bus-sized boa", and "Granddaddy of the snake world", among other things). The newly named Titanoboa cerrejonensis would have measured 13 metres long and weighed about 1,135 kilograms, making it the biggest known snake, living or extinct.

Why does this matter for climate predictions? The snake lived 58 to 60 million years ago, around the Palaeocene when the Earth's upper latitudes were much warmer than they are today. This was a time when ice at the poles had melted and crocodiles roamed the Arctic. But, as climate scientist Matthew Huber describes in a Nature News & Views article, researchers are less sure how hot the tropics were during that time.

Vertebrate paleontologist Jason Head of the University of Toronto in Canada and his colleagues, who reported the snake discovery in Nature, reasoned that such a large snake could only survive at a certain temperature. Snakes rely on external heat from their environment to help fuel their metabolism. The bigger the snake, the more heat it requires, which is why you don't see pythons in Minnesota.

The researchers used a model relating animal body size and ambient temperature to determine how hot the tropics must have been to support the snake. Today's tropics average 26-27 degrees Celsius, and the largest "verifiable" modern anaconda is 7.3 metres long, the study says. Assuming Titanoboa had a similar metabolic rate to today's snakes, the team calculated, the Palaeocene tropics must have been 30-34 degrees Celsius.

"We've taken the snake and turned it into a giant thermometer," says Head.

The finding suggests that as Earth's higher latitudes warmed up during the Palaeocene, the tropics got hotter as well. This goes against the argument that the Earth has a 'thermostat' mechanism that keeps tropical temperatures steady. And while the comparison between the natural global warming of the Palaeocene and modern human-induced global warming is "very tenuous", Head says, it might mean that today's tropics will heat up just as fast as the rest of the world, potentially leading to more extinctions around the equator.

Lisa Sloan, a climate scientist at the University of California, Santa Cruz, calls the study "intriguing". Although it would have been nice to get estimates from other large Palaeocene creatures as well, she says, the approach has "a lot of potential" for future research.

Image: Jason Bourque

Posted by Alex Witze on February 05, 2009
Categories: Palaeoclimate, Roberta Kwok | Permalink | Comments (1) | TrackBacks (0)

In the 70s and 80s, scientists from around the world worked to reconstruct Last Glacial Maximum (19,000 to 23,000 years ago) sea surface temperatures across the globe under the auspices of the Climate: Long Range Investigation, Mapping and Prediction (CLIMAP) project. Since then, a number of new proxies and seafloor coring and drilling projects have produced a wealth of additional data. In a new paper online this week in Nature Geoscience (subscription required), the MARGO (Multiproxy Approach for the Reconstruction of the Glacial Ocean surface) team members have updated this reconstruction using all the newly available data.

Continue reading "CLIMAP for the 21st century" »

Posted by Alicia Newton on January 20, 2009
Categories: Alicia Newton, Palaeoclimate, Research | Permalink | Comments (0) | TrackBacks (0)

A Chinese expedition is expected to start work this week on a new Antarctic base that will faciliate novel research in climate science as well as in other fields, reports Jane Qiu over on Nature News [subscription].

The Kunlun base will be located at Dome Argus, or 'Dome A', some 4,093 metres above sea level. It will be China's third Antarctic research facility and is being built as a legacy of International Polar Year, a major two-year scientific programme that comes to an end in March.

According to radar studies of the region, Dome A sits atop ice over 3,000 metres thick. Scientists hope that extracting ice cores of that depth at this particular site could extend the record of past climate changes back to 1.5 million years. Qiu writes:

A key focus of research is finding sites where ice cores stretching back further in time than any others could be drilled. A core obtained at a site known as Dome C — about 1,000 kilometres from Dome A (see map) — reached 3,200 metres deep and helped to reconstruct past climate going back 800,000 years. Many believe that Dome A promises older ice because it is higher and has less snow, meaning that researchers can get more years of climate records in a given thickness of ice.

Work on the station is expected to be completed by January 28, before temperatures drop tobelow –50 °C. At that stage it will have room for 25 people, with 11 sleeping units. I'm guessing they use that rotational bed-sharing system scientists sometimes use at sea?

Olive Heffernan

Image:P. Huybrechts, Vrije Universiteit Brussel

Posted by Olive Heffernan on January 07, 2009
Categories: Cryosphere, Features, In the News, Olive Heffernan, Palaeoclimate, Research | Permalink | Comments (0) | TrackBacks (0)

A paper this week in Nature (subscription) sheds new light on the causes of pronounced greenhouse-gas and climate fluctuations during glacial times.

The last ice-age, which covered the period from around 110,000 to 10,000 years before now, is famed for a series of climate swings known as Dansgaard-Oeschger events.

Scientists have found evidence in Greenland ice cores for abrupt warming episodes of up to 15 degrees Celsius within few decades, followed by a more gradual cooling. These glacial warm and cold periods swung back and forth between the poles in a kind of thermal seesaw effect, whereby Antarctic temperatures rose when Greenland temperatures dropped, and vice versa.

It has long been assumed that Dansgaard-Oeschger events were triggered by changes in Atlantic ocean-circulation. The new modelling study by Andreas Schmittner and Eric Galbraith now adds new evidence to the idea. Weakening Atlantic meridional overturning circulation, the heat conveyor which carries warm water surface water northwards and cold deep-water back south, is indeed the primary physical mechanism driving glacial climate fluctuations, they conclude. Here’s an editor’s summary.

Schmittner and Galbraith carried out simulations with a coupled model of glacial climate and (simplified) biogeochemical cycles. When they manipulated the Atlantic circulation – artificially ‘switching’ it off and on in their model, that is - the model nicely reproduced the temperature changes typical for Dansgaard-Oeschger events. Remarkably, the model also reproduced reasonably well the ice-core-derived changes in atmospheric concentrations of the greenhouse-gases carbon dioxide and nitrous oxide which accompany such events.

Continue reading "Glacial climate swings: It’s in the ocean" »

Posted by Quirin Schiermeier on November 20, 2008
Categories: Climate Science, Ocean science, Palaeoclimate, Quirin Schiermeier, Topics | Permalink | Comments (0) | TrackBacks (0)

If carbon dioxide is trump, then methane is the joker in the greenhouse game. The flammable gas (CH4) is produced in wetlands, landfills and in the guts of cattle and sheep, and it is stored in vast amounts in so-called clathrates, or gas hydrates, in the ocean floor.

The latter stuff has always kindled imagination. In the 1930s, dumbfounded Russian sailors who had lit dynamite for navigational purposes in the Siberian Arctic reported that the air around them started to burn. Had they set on fire methane released from clathrate reservoirs? Perhaps.

Less likely is that methane bubbling up from the ocean floor can makes the water so foamy that ships floating above sink like a rock. File this under Bermuda triangle myths.

But catastrophic methane bursts do seem to be linked with anomalous warming episodes in the Earth’s past, such as the one that occurred at the Palaeocene-Eocene Thermal Maximum around 55 million years ago. Dissociating clathrates may well have been the culprit then.

What had uncorked the bottle is unclear. But in any case, reports this week of methane emissions from sub-sea permafrost beneath the Siberian shelf, and from the seabed off Svalbard, sound alarming.

Geologists assume there are large methane hydrate reservoirs in both regions. Are they beginning to destabilize? Have we lit a time bomb? Is global warning getting out of control?

Media reports this week imply all this, some more and some less cautiously. It’s a wonderful story of course: Weird things happening in the Arctic, strange tales from the bottom of the ocean, Apocalypse Soon! It’s new, it’s exciting, it’s scary - no wonder journalists love it.

But wait a minute. The methane system discovered off Svalbard has probably been active for thousands of years, it’s only that no-one has ever looked for it.

The methane emissions detected in the Laptev Sea are also not a new phenomenon. Russian scientists have observed methane plumes there since the mid-1990s when they began to regularly visit the remote and inaccessible region. It does seem that there are many more, and possibly more vigorous, emission hotspots than was previously thought. But observations are still few; it’s not too much of a surprise that the harder they look the more they will find. I have tried to put the recent discoveries in context in my news story here.

That’s not to say that rising methane emissions, and thawing permafrost, are no concerns. They are, and their sources and causes need to be studied carefully. Long-overlooked methane emissions from living plants, as were just recently confirmed, are proof enough for how poorly methane cycles are actually understood.

But not only in matters climate change there’s a danger of confusing people by media coverage that alternates between alarmism and appeasement. Andrew Revkin of the New York Times has appositely termed the effect a journalistic whiplash for the public.

Science, although intrinsically a never-ending process, will every so often generate journalistic scoops - and sometimes journalistic kitsch. The methane story is exciting, but inflationary use of ‘dramatic’, 'alarming' etc in science stories produces only cheap thrills.

Quirin Schiermeier

Posted by Quirin Schiermeier on September 28, 2008
Categories: Recent contributors, Biosphere feedbacks, GHG emissions, In the News, Ocean science, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (2) | TrackBacks (0)

Cross posted from The Great Beyond

The contentious ‘hockey stick’ climate change graph has again been upheld as broadly accurate, doubtless to the rage of climate denialists/sceptics/whatevers.

A team led by Michael Mann of Penn State University has looked at a whole range of proxies for surface temperatures over the last 2,000 years in an attempt to counter criticism of the graph, which showed a long ‘handle’ and a sharp upturn (the blade).

Their findings? As the Christian Science Monitor puts it: “It still looks a lot like the much-battered, but still rink-ready stick of 1998. Today the handle reaches further back and it’s a bit more gnarly. But the blade at the business end tells the same story.”

The previous hockey stick had been accused of relying too much on data from tree rings so this PNAS study may silence some of the critics when it appears later.

Continue reading "Jolly hockey sticks " »

Posted by Olive Heffernan on September 02, 2008
Categories: Climate Science, Climate variability, Daniel Cressey, Features, In the News, Palaeoclimate | Permalink | Comments (4) | TrackBacks (0)

An elegant Reuters headline from the paleoclimate world:

Climate chill came exactly 12,679 years ago: study

I got a kick out of this story, having read Gavin Schmidt and Elisabeth Moyer’s NRCC op-ed last week on the chilly gap between paleoclimatologists and climate modellers (and the perhaps-even-chillier one between climate scientists and economists). Schmidt and Moyer point out that while the paleo crowd may “assume that modellers have a myopic view of climate history”, modellers “may assume that palaeo-science is too anecdotal, qualitative and localized to be of use for quantitative modelling.”

Per that headline, however, paleo researchers occasionally make delightfully precise statements - when they get their hands on a sample that yields data at the right timescale. But even then, connecting snapshots of the past with future climate scenarios is not straightforward.

Continue reading "The year the climate changed" »

Posted by Anna Barnett on August 04, 2008
Categories: Anna Barnett, In the News, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

Isotope chemistry is a bit of an arcane world for the non-initiated. But variants of elements that differ only in the number of neutrons in their nuclei are common tools of the trade of archaeologists, geologists and climate researchers.

In the past 50 years, a much-improved chronology of past climatic events has evolved through analyses of the oxygen isotope record of marine shells and minerals in deep-sea and lake sediments. But information about the Earth’s deep geological past, in particular concerning the chemical composition of the atmosphere, is still hard to get by.

The debut of a new stable mineral-isotope proxy for ancient atmospheric condition is therefore a remarkable event, the editors of a paper in this week’s Nature note in their summary.

When analysing the triple oxygen isotope composition of ancient sulphate deposits, a team of geophysicists led by Huiming Bao of Louisiana State University found that they exhibit variable negative oxygen-17 anomalies over the past 750 million years. They propose that these small anomalies, first noticed a few years ago in a study unrelated to atmospheric chemistry, reflect those of atmospheric oxygen and carbon dioxide in the past.

The new proxy is hardly sensitive enough to record the relatively subtle variations in atmospheric oxygen and carbon dioxide content during the Pleistocene, the Earth’s recent period of repeated glaciations.

It could be useful, though, when evaluating extreme climates much earlier in our planet’s history. For example, oxygen-17 anomalies in barite sulphates display a negative spike – hinting at an extremely high level of atmospheric carbon dioxide - around 635 million years ago, when the Earth was likely recovering from a period of global glaciation in the Early Cambrian. This finding supports the not undisputed ‘snowball’ Earth hypothesis and/or massive methane release in the aftermath of Neoproterozoic glaciation

Quirin Schiermeier

Posted by Quirin Schiermeier on May 22, 2008
Categories: Atmospheric Science, Climate Science, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (0) | TrackBacks (0)

The Earth’s greenhouse history of the last 800,000 years is an open book now, thanks to years of detective work by two large international teams of climate scientists.

Nature has two papers this week, here and here, about the levels of atmospheric concentration of the two main greenhouse gases – carbon dioxide and methane – as derived from air entrapped in the EPICA Dome C ice core from Antarctica. Here is an editor's summary.

The first and foremost results: The present day concentration of both gases is higher than has ever been the case in the past 800,000 years. Also, the ups and downs in carbon dioxide and methane curves follows the succession of cold glacial climates and relatively warm periods (such as ours) in between. An 800,000 year temperature record had been reconstructed previously from Antarctic ice cores.

Together, the results provide powerful evidence for a strong link between greenhouse gases and climate. During most of the Earth’s history greenhouse gas concentrations have fluctuated in the absence of humans burning coal and other fossil fuels. But the unprecedented rise of greenhouse gases in the modern atmosphere, to concentrations which threaten to unhinge vital components of the Earth’s climate system, is clearly the result of human activity.

In the past, greenhouse gas concentrations have varied owing to subtle feedbacks between orbital changes and oceanic and terrestrial carbon cylcles. Carbon dioxide concentrations depend on oceanic uptake, whereas methane is linked with the size and distribution of wetlands releasing the gas.

Like all good science, the new data will raise many new questions. One is why the amplitude of the 100,000-year oscillation in methane and carbon dioxide concentrations (which correlates with the 100,000 year temperature cycle) has changes so markedly around 450,000 years ago. Warm periods in the more recent history of the Earth seem to have been warmer than the interglacials prior to 450,000 years ago. Carbon dioxide and methane concentrations mirror this trend, which might hint to the existence of a longer-term cycle not visible in the existing record.

Another question is how greenhouse gas concentrations measured in Antarctic ice cores relate to episodes of rapid warming and cooling in Greenland and the northern hemisphere. It seems that more that 70 such temperature jumps, perhaps as a result of changes in ocean circulation, have occured over the last 800,000 years.

“These new benchmark data for greenhouse-gas variability pose questions as to what a much longer record might show,” writes Ed Brook in a news and views article. The search for the best drilling site which could produce such a record is beginning.

Quirin Schiermeier

Posted by Quirin Schiermeier on May 15, 2008
Categories: Climate Science, Climate variability, Features, Journal Club, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (0) | TrackBacks (0)

With an uninterrupted 17-million year sediment record of Antarctic’s climatic past now available, scientists are hoping for unique new insights into the continent’s climatic past.

A few initial results of the Antarctic Geological Drilling programme (ANDRILL) were announced last week at the general assembly of the European Geosciences Union in Vienna. There is an online news story here.

Antarctica’s ice sheets, so it seems, respond more sensitively to climate fluctuations than has been assumed. During warmer periods, the West Antarctic Ice Sheet and its floating extension, the western Ross Ice Shelf, have shrunk substantially. Some 3.5 million years ago the ice seems to have disappeared completely for around 200,000 years. There were snow-capped mountains, alpine trees, gushing rivers, quiet lakes – the frozen continent was a place where you would love to go fishing or hiking, were it not for the midges.

The world was warmer then than it is today, but not substantially so. If temperatures continue to rise, glaciers in Antarctic’s warmer western part might begin to retreat again before long. A few million years ago, Antarctic melting probably raised sea levels globally by 10 metres or so. If history repeats itself, we’re headed for trouble.

Quirin Schiermeier

Posted by Quirin Schiermeier on April 24, 2008
Categories: Recent contributors, Categories, Conferences and Meetings, EGU 2008, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (5) | TrackBacks (0)

(Posted by Olive on behalf of Hans)

In October 2004 we were lucky to publish in Science our critique of the ‘hockey-stick’ reconstruction of the temperature of the last 1000 years. Now, two and half years later, it may be worth reviewing what has happened since then.

The publication in 2004 was a remarkable event, because the hockey-stick had been elevated to an icon by the 3rd Assessment Report of the IPCC. This perception was supported by a lack of healthy discussion about the method behind the hockey-stick. In the years before, due to effective gate keeping of influential scientists, papers raising critical points had a hard time or even failed to pass the review process. For a certain time, the problem was framed as an issue of mainstream scientists, supporting the concept of anthropogenic climate change, versus a group of skeptics, who doubted the reality of the blade of the hockey stick. By framing it this way, the real problems, namely the ‘wobbliness’ of the shaft of the hockey-stick, and the suppressing of valid scientific questions by gate keeping, were left out.

Hopefully, sociology of science will later study this unfortunate period of climate science, but we may conclude now that science itself has indeed corrected claims of premature knowledge. We see now a healthy and broad discussion of the issue. We had the opportunity to respond to no less than four comments on our 2004 Science paper, but unfortunately only two comments were published. Similarly, Michael Mann and his coworkers had to respond to at least 2 comments to their Journal of Climate article in 2005.

At the EGU General Assembly a few weeks ago there were no less than three papers from groups in Copenhagen and Bern assessing critically the merits of methods used to reconstruct historical climate variable from proxies; Bürger’s papers in 2005; Moberg’s paper in Nature in 2005; various papers on borehole temperature; The National Academy of Science Report from 2006 – al of which have helped to clarify that the hockey-stick methodologies lead indeed to questionable historical reconstructions. The 4th Assessment Report of the IPCC now presents a whole range of historical reconstructions instead of favoring prematurely just one hypothesis as reliable.

When looking back we are satisfied with what has been achieved – namely an open, open-minded exciting discussion about the merits and problems related to different methods; an atmosphere where mere claims about the informational content of proxy-data meet a more critical response; an evolving practice of testing the skill of reconstruction methods in the laboratory of millennial forced global climate model simulations, where the formation of proxy-data is simulated in - so far too simplified - models.

Hans von Storch and Eduardo Zorita

Posted by Olive Heffernan on May 03, 2007
Categories: Climate Science, Hans von Storch, Palaeoclimate | Permalink | Comments (36) | TrackBacks (1)