Except for a few pockets of warming along the West Antarctic coast, surface air temperatures have cooled profoundly across East Antarctica – most of the continent, as well as the surrounding Southern Ocean – in the last 40 years (1979-2018). About 30% of the cooling can be explained by Madden-Julian Oscillation forcing.
Atmospheric CO2 concentrations rose from 337 ppm in 1979 to 408 ppm in 2018.
But according to graphical illustrations of surface air temperature (SAT) trends from satellite observations documented in a new study (Hsu et al., 2021), nearly the entire continent of Antarctica and much of the surrounding Southern Ocean have undergone about -0.02°C/year (-0.2°C per decade) SAT cooling during this period.
East Antarctica’s temperatures have fallen by about 1°C in the last 40 years, with approximately -0.4°C cooling from 1999-2018 relative to 1979-1998.
Per the authors, one-third of this 40-year cooling trend can be attributed to Madden-Julian Oscillation (MJO) forcing. The MJO influence is “likely to accelerate” the long-term cooling trend for East Antarctica in the coming decades.
Glaciers in the Ötztal Alps in Austria are currently melting and may be lost within two decades, but this might not be the first time humans have seen this kind of change. A new analysis reveals that glaciers in this region formed just before or perhaps even within the lifetime of Ötzi the Iceman, a mummified body found just 12 kilometres away in 1991.
Pascal Bohleber at the Austrian Academy of Sciences in Vienna and his colleagues drilled 11 metres into the Weißseespitze summit glacier, down to the bedrock, at 3500 metres altitude and collected two ice cores. They then used radiocarbon dating to analyse microscopic bits of organic material extracted from the ice cores and found that the glacier is 5200 to 6600 years old. Ötzi is thought to have lived between 5100 and 5300 years ago, and his body was found preserved in ice.
The glacier’s age means it formed during a time called the mid-Holocene warm period, when Earth’s climate was warmer than it is now. It is also dome-shaped, which Bohleber says is rare in the Alps and means that the ice has seen very little movement over time, meaning we can use it to study the climate when it formed.
“More information on the mid-Holocene warm period, when the glaciers were smaller than today, is direly needed so that we can better predict how the glaciers will respond to the anticipated future climate over the next 50 years,” says Bethan Davies at Royal Holloway, University of London.
Comparing ice cores from different sites tells us quite a bit about the past climate in that region, says Bohleber, but that gets harder as the glaciers thaw. Meltwater makes it more difficult to drill for ice cores and causes the glaciers to slide downhill, exposing the ancient ice to modern contaminants.
In direct contradiction to the official forecast, a team of scientists led by the National Center for Atmospheric Research (NCAR) is predicting that the Sunspot Cycle that started this fall could be one of the strongest since record-keeping began.
In a new article published in Solar Physics, the research team predicts that Sunspot Cycle 25 will peak with a maximum sunspot number somewhere between approximately 210 and 260, which would put the new cycle in the company of the top few ever observed.
The cycle that just ended, Sunspot Cycle 24, peaked with a sunspot number of 116, and the consensus forecast from a panel of experts convened by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) is predicting that Sunspot Cycle 25 will be similarly weak. The panel predicts a peak sunspot number of 115.
Archaeologists have published a new paper in The Holocene, DOI: 10.1177/0959683620972775 that confirms what previous research has shown: numerous periods during recent history have been as warm as or warmer than the present.
The press release was covered in The New Scientist, “Climate change has revealed a huge haul of ancient arrows in Norway,” and discusses the findings of researchers from the Universities of Cambridge, Oslo, and Bergen. The researchers discovered a “treasure trove” of arrows, arrowheads, clothing, and other artifacts, recently uncovered by a receding ice in a mountainous region of southern Norway. The oldest arrows and artifacts date from around 4100 BC. The youngest artifacts date from approximately AD 1300, at the end of the Medieval Warm Period. Because present temperatures are only now exposing some of the artifacts were deposited when no ice covered the ground, temperatures were clearly warmer during the many periods when artifacts were deposited.
Along with the arrows and other artifacts, the researchers found nearly 300 specimens of reindeer antler and bone exposed by receding ice. Because reindeer presently frequent the area, the archaeologists say they are confident the area has served as an important hunting ground, off and on, for millennia.
The fact that artifacts were found from several different periods separated by hundreds and thousands of years in time indicates the ice and snow in the region has expanded and receded several times over the current interglacial period.
Elsewhere in Norway, scientists also recently uncovered what they have labeled a “Viking highway,” a route the ancient peoples inhabiting the region used to travel regularly. The route had for approximately 2,000 years been covered by snow and ice that expanded as the region’s climate shifted from a relatively warm period, comparable to present temperatures, to a colder period during which “permanent” thick snow and ice cover formed. This erected the equivalent of a “highway closed” sign.
During the last Ice Age about 20,000 years ago, iron-containing dust acted as a fertilizer for marine phytoplankton in the South Pacific, promoting CO2 sequestration and thus the glacial cooling of the Earth. But where did the dust come from? Researchers led by Dr. Torben Struve, geoscientist at the University of Oldenburg, Germany, have investigated this open question of climate history, which is also relevant with respect to current climate change.
Using sediment cores from the sea floor, they found that a large part of the dust deposited in the southern South Pacific at that time had travelled an extremely long way. Up to 80 percent of the dust came from what is now north-west Argentina, from where it was transported almost completely around the globe by the prevailing westerly winds. After a voyage of up to 20,000 kilometres, it contributed significantly to the increased input of iron into the glacial South Pacific. The dust input from Australia, which dominates in the South Pacific today, played only a minor role. The research team has published these new insights into the mechanisms of natural iron input into the Southern Ocean in the journal Nature Communications.
“We have analysed the chemical fingerprint of the dust and compared it with geological data from several continents. This was laborious work, like a jigsaw puzzle,” says Struve, a post-doctoral scientist in the research group “Marine Isotope Geochemistry” at the University’s Institute for Chemistry and Biology of the Marine Environment (ICBM). The team included researchers from his group as well as colleagues from the Alfred Wegener Institute – Helmholtz Centre for Polar and Marine Research, Bremerhaven (Germany), and from Columbia University, New York (USA).
A Texas A&M-led study analyzed ocean floor sediment cores to provide new insights into the relationship between deep ocean oxygenation and atmospheric carbon dioxide levels in the 50,000 years before the last ice age
Why do carbon dioxide levels in the atmosphere wax and wane in conjunction with the warm and cold periods of Earth’s past? Scientists have been trying to answer this question for many years, and thanks to chemical clues left in sediment cores extracted from deep in the ocean floor, they are starting to put together the pieces of that puzzle.
Recent research suggests that there was enhanced storage of respired carbon in the deep ocean when levels of atmospheric carbon dioxide concentrations were lower than today’s levels. But new research led by a Texas A&M University scientist has reached back even further, for the first time revealing insights into atmospheric carbon dioxide levels in the 50,000 years before the last ice age.
From 2008 to 2016 a widespread cooling ranging from 0.6°C to more than 2.0°C has chilled effectively the entire oceanic region from E. Canada to N. Iceland to S. Europe. The cooling persists year-round and extends from the surface down to depths of 800 m.
About 790,000 years ago, a meteor slammed into Earth with such force that the explosion blanketed about 10% of the planet with shiny black lumps of rocky debris. Known as tektites, these glassy blobs of melted terrestrial rock were strewn from Indochina to eastern Antarctica and from the Indian Ocean to the western Pacific. For more than a century, scientists searched for evidence of the impact that created these pitted blobs.
But the crater’s location eluded detection — until now.
Geochemical analysis and local gravity readings told researchers that the crater lay in southern Laos on the Bolaven Plateau; the ancient impact was concealed under a field of cooled volcanic lava spanning nearly 2,000 square miles (5,000 square kilometers), the scientists reported in a new study.
Was the crater buried? On Laos’ Bolaven Plateau, the scientists found a site where fields of volcanic lava might have hidden signs of an older meteor impact. In a region that the researchers targeted as a likely spot for a crater, most of the lava flows were also in the right age range: between 51,000 and 780,000 years old.
The study authors peered below the lava’s surface by taking gravity readings at more than 400 locations. Their resulting gravity map showed one area “of particular interest” with a gravitational anomaly, a subsurface zone less dense than the volcanic rock surrounding it. Their measurements hinted at an elliptical, “elongated crater” about 300 feet (100 m) thick, about 8 miles (13 km) wide and 11 miles (17 km) long, according to the study.
Together, all of these clues suggested that “this thick pile of volcanic rocks does indeed bury the site of the impact,” the scientists wrote.
Dry summers were not rare 1000 years ago. Researchers from the University of Greifswald’s research group ‘Landscape Ecology and Ecosystem Dynamics’ have been able to reconstruct 1000 years of the dry summer period in northern Germany.
Beech forest – photo: Dr. Tobias Scharnweber
The article ‘Removing the no-analogue bias in modern accelerated tree growth leads to stronger medieval drought’ was published in 2019’s February edition of the journal Scientific Reports.
As part of the current collaborative research project BaltRap (The Baltic Sea and its Southern Lowlands: Proxy-Environment interactions in times of rapid changes), the researchers investigated growth rings in nearly 2000 living beech trees – including some from the university’s own Elisenhain forest – and archaeological wood used for construction from around 1000 A.D. The growth rings found in this wood are a unique archive of previous environmental conditions. If the climatic conditions are good, growth rings are wide; in unfavourable years, like in dry 2018, there is little growth. Dendroclimatology uses this correlation to reconstruct past environmental conditions.
by Indriani Roy, September28, 2018 in FrontiersinEarthScience
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom
The puzzle of recent global warming trend slowdown has captured enough attention, though the underlying cause is still unexplained. This study addresses that area segregating the role of natural factors (the sun and volcano) to that from CO2 led linear anthropogenic contributions. It separates out a period 1976–1996 that covers two full solar cycles, where two explosive volcanos erupted during active phases of strong solar cycles. The similar period also matched the duration of abrupt global warming. It identifies that dominance of Central Pacific (CP) ENSO and associated water vapor feedback during that period play an important role. The possible mechanism could be initiated via a preferential alignment of NAO phase, generated by explosive volcanos. Inciting extratropical Rossby wave to influence the Aleutian Low, it has a modulating effect on CP ENSO. Disruption of Indian Summer Monsoon and ENSO during the abrupt warming period and a subsequent recovery thereafter can also be explained from that angle. Interestingly, CMIP5 model ensemble, and also individual models, fails to comply with such observation. It also explores possible areas where models miss important contributions due to natural drivers.
La géologie, une science plus que passionnante … et diverse