Ida geht in Rente

Helmholtz-Zentrum Potsdam – Deutsches GeoForschungsZentrum GFZ:

Neues aus der Klimageschichte des Toten Meeres

Sedimentanalysen bisher unerreichter Genauigkeit zeigen Phasen der Stabilität während Zeiten starken Klimawandels – vor rund 15.000 Jahren. So sank der Wasserspiegel am Ende der letzten Eiszeit innerhalb weniger Jahrtausende um fast 250 Meter. Feuchte Phasen unterbrachen die Trockenheit. Eine heute erschienene Studie im Fachmagazin Scientific Reports bringt nun neue Erkenntnisse über den genauen Ablauf dieses Prozesses. Das bietet auch neue Erkenntnisse zur Siedlungsgeschichte dieser für die Menschheitsentwicklung bedeutenden Gegend, und ermöglicht bessere Einschätzungen aktueller und künftiger Entwicklungen, die vom Klimawandel getrieben sind.

Der Seespiegel des Toten Meeres sinkt derzeit jedes Jahr um mehr als einen Meter – nicht zuletzt wegen des starken Wasserverbrauchs im Einzugsgebiet. Aber auch aus früheren Zeiten sind sehr starke Seespiegelabsenkungen aufgrund von Klimaänderungen bekannt. So sank der Wasserspiegel am Ende der letzten Eiszeit innerhalb weniger Jahrtausende um fast 250 Meter. Eine heute erschienene Studie im Fachmagazin Scientific Reports bringt nun neue Erkenntnisse über den genauen Ablauf dieses Prozesses. Daniela Müller und Achim Brauer vom Deutschen GeoForschungsZentrum (GFZ) Potsdam haben dafür zusammen mit Kollegen der Hebrew University in Jerusalem 15.000 Jahre alte Sedimente aus dem Toten Meer und der Umgebung mit neu entwickelten Methoden untersucht. Sie zeigen mit bisher unerreichter Genauigkeit, dass die Phase starken Wasserspiegelabfalls durch einige zehn bis hundert Jahre andauernde feuchte Perioden unterbrochen wurde. Das bietet auch neue Erkenntnisse zur Siedlungsgeschichte dieser für die Menschheitsentwicklung bedeutenden Gegend, und ermöglicht bessere Einschätzungen aktueller und künftiger Entwicklungen, die vom Klimawandel getrieben sind.

Der Wasserkreislauf am Toten Meer – damals und heute

In hochsensiblen Regionen wie dem östlichen Mittelmeerraum, wo die Verfügbarkeit von Wasser ein wichtiger Faktor für die sozioökonomische und politische Entwicklung ist, ist es von entscheidender Bedeutung zu verstehen, wie sich der Wasserkreislauf als Reaktion auf den globalen Klimawandel verändert. Hierbei hilft auch ein Blick etliche Jahrtausende zurück. So sank der Wasserspiegel des Lisan-Sees während des Übergangs vom letzten Eiszeitalter zum warmen Holozän im Zeitraum vor etwa 24-11 Tausend Jahren um rund 240 Meter, was schließlich zu seinem Übergang in das heutige Tote Meer führte.

Sedimente als Zeitzeugen

Die Sedimente am Rand des Lisan-Sees nahe der Felsenstadt Masada und aus der Tiefe des heutigen Toten Meeres sind einzigartige Zeugen dieser Entwicklung. Forschende um die Doktorandin Daniela Müller und den Leiter der Sektion 4.3 „Klimadynamik und Landschaftsentwicklung“ Achim Brauer vom Deutschen GeoForschungsZentrum Potsdam analysierten in ihrer neuen Studie gemeinsam mit Kollegen vom Geological Survey Israel und der Hebrew University in Jerusalem diese Sedimente mit bislang unerreichter Genauigkeit. Die Untersuchungen fanden im Rahmen des PALEX-Projektes ‚Paleohydrology and Extreme Floods from the Dead Sea ICDP Core‘ statt, das von der Deutschen Forschungsgemeinschaft (DFG) finanziert wird.

Neue hochauflösende Methoden zur Sedimentanalyse

Für diese Studie wurden am GFZ neue hochauflösende analytische Verfahren entwickelt, um aus der Schichtung der Sedimente und ihrer geochemischen Zusammensetzung genauen Aufschluss selbst über jahreszeitliche Ablagerungsprozesse und so über Art, Dauer und Verlauf klimatischer Phasen zu gewinnen.

Neu ist insbesondere die Kombination von Lichtmikroskopischen Verfahren mit dem sogenannten 2D-Element Mapping mittels Röntgenfluoreszensscanner. Das ermöglicht eine genaue Identifikation und Lokalisation von Elementen in den Sedimenten. Wichtig und herausfordernd ist dafür die Präparation der Proben: Ihnen muss durch Gefriertrocknung die Feuchtigkeit entzogen werden – nicht einfach bei dem hohen Salzgehalt des Toten Meeres und dessen Affinität für Wasser. Dann werden die Sedimente in Kunstharz eingegossen und daraus dann Dünnschliffe gefertigt. Bei alledem darf die Mikrostruktur der Sedimente nicht verändert werden.

Pause im Klimawandel: Feuchte Phasen unterbrachen lange Trockenzeiten

Die Forschenden haben herausgefunden, dass der dramatische Abfall des Seespiegels vor etwa 15.000 Jahren aufgrund zunehmender Trockenheit mehrfach durch feuchtere Phasen unterbrochen wurde, der Klimawandel also Pausen einlegte. „Wir konnten in dieser Studie erstmals die Dauer dieser Phasen mit einigen Jahrzehnten und in einem Fall bis zu Jahrhunderten durch die Zählung von Jahresschichten im Sediment genau bestimmen“, sagt Daniela Müller, Erstautorin der Studie. Der genaue Grund für diese Pausen des Klimawandels dieser Region ist jedoch noch nicht klar. Es wird ein Zusammenhang mit dem Klimageschehen im Nordatlantik vermutet.

„Besonders überraschend war, dass es während dieser feuchteren Phasen teilweise über mehrere Jahrzehnte auch keine extremen Hochwasser gegeben hat, die sonst für diese Region auch heute noch typisch sind“, erläutert Müller.

Konsequenzen für archäologische Betrachtungen und kommende Klimaszenarien

Diese Ergebnisse sind auch für archäologische Betrachtungen von Interesse, weil sie mit der Zeit der Sesshaftwerdung der Natufischen Kultur in dieser Region zusammenfallen. Klimatisch stabile Phasen könnten die kulturellen Entwicklungen begünstigt haben.

„Die Studie zeigt, dass starke klimatische Änderungen in der Vergangenheit sehr dynamisch verlaufen sind und auch kurze Phasen relativer Stabilität einschließen können. Wir lernen daraus, dass Klimawandel nicht linear verläuft, sondern Phasen starker Änderungen mit stabileren Phasen abwechseln“, betont Achim Brauer.

Paper: Müller, D., Neugebauer, I., Ben Dor, Y. et al. Phases of stability during major hydroclimate change ending the Last Glacial in the Levant. Sci Rep 12, 6052 (2022). DOI: 10.1038/s41598-022-10217-9
https://doi.org/10.1038/s41598-022-10217-9

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Chinese Academy of Sciences:

Groundwater extraction affects hydrological process over Beijing-Tianjin-Hebei region in Northern China

The rapid development of agriculture and industry in the Beijing-Tianjin-Hebei region leads to an increase in water demand. Excessive groundwater extraction often results in the water depletion that may affect ecological and hydrological processes.

Groundwater depletion can be detected using in-situ observations, gravity recovery and climate experiment data, and simulations.

Recently, a joint research team led by researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences investigated the effects of groundwater extraction on hydrological process and energy cycle in Beijing-Tianjin-Hebei by high resolution simulations.

Their study was published in Journal of Hydrology.

„Human groundwater extraction deepened the groundwater table depth between 2000 and 2012 across the plains in front of Taihang Mountain,“ said Prof. Jia Binghao, the corresponding author of the study. „Groundwater extraction used for irrigation changed the water and energy budgets, leading to a significant increasing of latent heat flux within the growing season.“

According to this study, groundwater extraction rapidly reduced terrestrial water storage (TWS, exceeding 24 cm per unit area) from 2000 to 2012. TWS changes in 52% of urbanized areas are dominated by groundwater extraction, and 20% of urbanized areas are dominated by evapotranspiration.

„The model in this study can be used for other groundwater extraction hotspots around the world, such as Europe, southern Iran, central United States, northern India, and Pakistan to study the impact of human water use,“ said Prof. Xie Zhenghui, one co-author of the study.

Paper: Longhuan Wang et al, Impact of groundwater extraction on hydrological process over the Beijing-Tianjin-Hebei region, China, Journal of Hydrology (2022). DOI: 10.1016/j.jhydrol.2022.127689

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phys.org:

A nasty I of the storm: Ida is 12th I hurricane name retired

There’s something about hurricanes starting with the letter I that is particularly nasty. Last year’s Ida now joins the list of storms so deadly their names don’t get used again.

The World Meteorological Organization said Wednesday that it was retiring the name „Ida“ from its list of Atlantic hurricane names that repeats every six years. Ida caused $75 billion damage in the U.S. and killed 55 people in a swath of destruction from Louisiana to New England.

Ida, a category four storm, caused about $55 billion in flooding damage and killed six people in Louisiana when it made landfall, but its heavy rains and flooding killed 49 people in the Mid-Atlantic and Northeast. It is the fifth costliest storm in U.S. history behind Hurricanes Katrina, Harvey, Maria and Sandy, all also retired, said National Hurricane Center senior hurricane specialist Daniel Brown, who is on the WMO committee that retires names.

Weiterlesen auf phys.org

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National Center for Atmospheric Research:

New method can predict summer rainfall in the Southwest months in advance

As reservoir levels dwindle in the arid southwestern United States, scientists have developed a method to estimate summer rainfall in the region months in advance. Such seasonal predictions can help state and local officials make key reservoir storage and water allocation decisions earlier in the season and support more efficient water management.

Current seasonal forecasts are not able to accurately predict summer rains across Arizona and New Mexico. However, a team of scientists found that a variable in those same forecasts—the amount of water vapor in the lower atmosphere—could, starting in April, predict precipitation trends between the months of June and October across a large part of the region, performing especially well in Arizona. They detailed their findings in a study in Geophysical Research Letters.

„The method is surprisingly successful, enabling us to look at individual catchments and correctly predict months ahead of time whether they will get above or below average rainfall,“ said Andreas Prein, a scientist at the National Center for Atmospheric Research (NCAR) who led the study. „It’s exciting because the desert Southwest is one of the most water-stressed regions in the world, and water management decisions have to be made way in advance before rainfall occurs.“

Unlike some research findings, this one will be put to the test immediately. The U.S. Bureau of Reclamation, which provided funding for the study, will evaluate the prediction system in the Southwest this year in both the Colorado River and Rio Grande basins. Reclamation manages water resources and operates hundreds of reservoirs, and several of its hydrologists worked on the study with NCAR. The study also received funding from the U.S. National Science Foundation, which sponsors NCAR.

„We are optimistic that this method will lead to some breakthroughs in forecasting inflows on the lower Colorado River and improved operations in the basin,“ said Shana Tighi, a hydrologist with Reclamation’s Lower Colorado Basin Region and a study co-author.

„Monsoon forecasting has long been a particular challenge in the Rio Grande Basin in New Mexico, where the monsoons can provide a significant portion of the water supply but have long been considered unpredictable,“ said Dagmar Llewellyn, another study co-author and supervisor of the water planning group in the Albuquerque Office of Reclamation. „This new technique has promise to allow significant improvements in water

Contending with water scarcity

Water scarcity is a major challenge for the U.S. Southwest. The region is contending with one of its most severe droughts in decades, even as temperatures are becoming hotter and water demands are increasing from a fast-growing population. Mountain snowpack supplies much of the water in reservoirs, but snow levels are diminishing, a trend that is expected to continue with climate change.

To help offset the loss of snowpack, water managers would like to make better use of rainfall from the North American Monsoon. This annual climate phenomenon, which results from southerly winds bringing moisture from the Pacific Ocean, Gulf of California, and Gulf of Mexico during much of the summer and early fall, delivers approximately 60-80% of the annual precipitation in the desert Southwest. But it is highly variable from one year to another, and scientists have not been able to accurately predict whether an upcoming monsoon season will deliver an average amount of rainfall, or be particularly wet or dry.

Prein and his co-authors turned to the long-range forecasts of several leading weather models to see whether they could develop months-ahead predictions of the monsoon. Although such forecasts are unreliable when predicting rain, they are more accurate in showing larger-scale atmospheric conditions, such as high- and low-pressure systems.

The study team applied a specialized algorithm to each of the weather models, trying to tease out whether any of 12 atmospheric variables, including temperature, humidity, winds, and atmospheric pressure at different heights, could be correlated with monsoon rainfall variability at selected Arizona and New Mexico catchments from 1982 to 2018. They conducted the analysis on the Cheyenne supercomputer at the NCAR-Wyoming Supercomputing Center.

This process enabled them to determine that one of the models, which is run by the European Centre for Medium-Range Weather Forecasts and is well regarded for reliable predictions of atmospheric conditions, can be used to predict monsoonal rainfall. When that model generated long-range forecasts in April of low-level atmospheric moisture during upcoming summer months, the scientists successfully correlated the moisture with the amounts of monsoonal rain that actually fell during those months.

The correlation was significant in each of the catchments in the study except southern New Mexico. The reasons the forecasts were better in Arizona than in New Mexico are being investigated by the scientists, but are likely attributable to the more complex atmospheric processes driving the New Mexico monsoon.

By calculating the number of days in which the lower atmosphere contained a large amount of moisture, the scientists were able to produce a monthly forecast that showed how rainfall at the catchments would compare with the historical average.

„The number of moist days is highly correlated with how much rainfall you get in a catchment,“ Prein said.

Prein and his colleagues are now planning to test the method on winter precipitation in the West. He said the method may also be applied to other regions.

„The framework itself is very generalizable and can be applied to a variety of different regions and different seasons,“ Prein said. „This points the way to better seasonal predictions for water resource management across the United States as well as other parts of the world.“

Paper: Andreas F. Prein et al, Sub‐Seasonal Predictability of North American Monsoon Precipitation, Geophysical Research Letters (2022). DOI: 10.1029/2021GL095602

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Sven Titz in der NZZ:

Oft heisst es, als Massnahme gegen den Klimawandel müsse man unbedingt das Bevölkerungswachstum bremsen – doch so eindeutig ist die Sache nicht

Noch wächst die Weltbevölkerung, wie Fachleute von den Vereinten Nationen melden, aber die Wachstumsrate sinkt. Auch politische Gründe sprechen gegen bevölkerungspolitische Massnahmen.

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University of New South Wales:

We must halve our energy use to avoid climate catastrophe, according to new modelling

Renewable energy transition won’t come fast enough to solve the climate crisis—we also need to reduce global energy consumption, according to new research from UNSW Sydney.

The research, published recently in Climate Policy, models different energy-use scenarios for reducing global energy-related CO2 emissions to zero by 2050. It found that simply substituting fossil fuels with renewable energy at current energy usage levels is no longer enough.

To keep global heating below 1.5°C—the level necessary to avoid irreversible damage—total energy consumption itself needs to halve over the next three decades based on 2019 levels. Furthermore, to keep temperature from overshooting a 1.5°C increase by 2050, global CO2 emissions must decline by about half by 2030.

Despite significant growth in renewable energy, it is being outstripped by the parallel increase in total energy consumption, primarily driven by growth in fossil fuels for areas like transportation and heating. And while energy usage did slightly decline during 2020 due to the pandemic, the demand has since returned.

Weiterlesen bei der University of New South Wales

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Mark Diesendorf auf The Conversation:

Net zero by 2050 will hit a major timing problem technology can’t solve. We need to talk about cutting consumption

Many climate activists, scientists, engineers and politicians are trying to reassure us the climate crisis can be solved rapidly without any changes to lifestyle, society or the economy.

To make the vast scale of change palatable, advocates suggest all we have to do is switch fossil fuels for renewable power, electric vehicles and energy efficiency technologies, add seaweed to livestock feed to cut methane and embrace green hydrogen for heavy industries such as steel-making.

There’s just one problem: time. We’re on a very tight timeline to halve emissions within eight years and hit net zero by 2050. While renewables are making major inroads, the world’s overall primary energy use keeps rising. That means renewables are chasing a retreating target.

My new research shows if the world’s energy consumption grows at the pre-COVID rate, technological change alone will not be enough to halve global CO₂ emissions by 2030. We will have to cut energy consumption 50-75% by 2050 while accelerating the renewable build. And that means lifestyle change driven by social policies.

Weiterlesen auf The Conversation