So kann das Grundwasser wieder aufgefüllt werden


KLIMA: Evolution im Eilverfahren

Korallen sind vom Klimawandel bedroht wie kaum ein anderes Lebewesen. Meeresökologe Christian Wild will ihr Überleben sichern


FOCUS: Es soll Riffe geben, die der Erwärmung trotzen.

Wild: Aber ja. Als ich vor Kurzem im Roten Meer tauchen war, habe ich auch Situationen wie vor 20 Jahren erlebt. Da gab es eine riesige Vielfalt von gesunden Korallen und Massen an Fischen – einfach wunderschön. Wir gehen davon aus, dass Steinkorallen im nördlichen Roten Meer eine Art Klimagedächtnis ausgebildet haben, weil sie schon seit Millionen Jahren starken Temperaturschwankungen ausgesetzt sind. Zugute kommt den Riffen dort auch, dass sie nicht noch weiteren Stressfaktoren ausgesetzt sind, also von der Landwirtschaft kontaminierten Flüssen, die ins Rote Meer münden.


Wild: Die Zucht von Korallen mithilfe der assistierten Evolution zur anschließenden Wiederaufforstung: Sie kann uns helfen, Zeit zu gewinnen, bis wir den Klimawandel in den Griff bekommen haben. Dabei werden in der Korallenlaiche, die typischerweise einmal im Jahr stattfindet, Geschlechtsprodukte von unterschiedlichen Korallen gezielt mithilfe von Netzen abgefischt. Das sind Bündel aus Spermien und Eizellen, die man mit bloßem Auge sieht.

Die werden dann im Labor miteinander vermischt, sodass Korallenbabys entstehen, die man dann für eine nachhaltige Wiederaufforstung verwenden kann. Das Schöne an der Methodik ist, dass man nichts Intaktes kaputtmacht, um etwas Kaputtes zu reparieren. Und so kann man eben auch bestimmte Merkmale wie eine hohe Hitzetoleranz züchten. Der nächste Schritt wäre eine Manipulation an den Genen.


Alarm in BILD:

Globale Studie: Grundwasser geht weltweit drastisch zurück

Weltweit sinkt das Grundwasser. Das ist nicht neu, aber wie rapide der Verlust in den letzten zwei Jahren war, macht Forschern Sorgen.

Lösung auf The Conversation (dort auch Abbildungen und Videos):

Humans are depleting groundwater worldwide, but there are ways to replenish it

If you stand at practically any point on Earth, there is water moving through the ground beneath your feet. Groundwater provides about half of the world’s population with drinking water and nearly half of all water used to irrigate crops. It sustains rivers, lakes and wetlands during droughts.

Groundwater is a renewable resource, but it can take decades or even centuries for some aquifers to recover after they are depleted. Current understanding of this challenge is based mainly on where and how frequently people record measurements of water levels in wells.

In a newly published study, our team of data scientistswater specialists and policy experts compiled the first global-scale dataset of these levels. We analyzed millions of groundwater level measurements in 170,000 wells located in over 40 countries and mapped how groundwater levels have changed over time.

Our study has two main findings. First, we show that rapid groundwater depletion is widespread around the world and that rates of decline have accelerated in recent decades, with levels falling by 20 inches or more yearly in some locations. Second, however, our research also reveals many cases where deliberate actions halted groundwater depletion. These results show that societies are not inevitably doomed to drain their groundwater supplies, and that with timely interventions, this important resource can recover.

Portrait of a thirsty planet

Many factors determine groundwater levels, including geology, climate and land use. But groundwater levels that are dropping deeper and deeper in a particular location often signal that people are pumping it out faster than nature can replenish it.

Some of the 300 million measurements we compiled were recorded by automated measuring devices. Many others were made in the field by people around the globe. And these measurements paint a worrying picture.

They show that groundwater levels have declined since the year 2000 in far more places than they rose. In many locations, especially arid zones that are heavily farmed and irrigated, groundwater levels are falling by more than 20 inches (0.5 meters) per year. Examples include Afghanistan, Chile, China, Peninsular India, Iran, Mexico, Morocco, Saudi Arabia, Spain and the U.S. Southwest.

Our second and more concerning finding is that in about one-third of the areas where we compiled measurements, the rate of groundwater decline is accelerating. Accelerated groundwater decline is common in dry climates where large swaths of land are used for agriculture. This suggests a potential link between groundwater-fed irrigation and intensifying groundwater depletion.

What happens when groundwater is overused?

Rapid and accelerating groundwater-level declines have many harmful effects.

Drinking-water supplies from wells and springs can run dry when groundwater levels decline. People and communities who rely on those wells can lose access to what may be their sole source of accessible fresh water for drinking.

For example, wells that supply fresh water to homes are running dry in California’s San Joaquin Valley, where groundwater depletion has accelerated since the early 2000s. This problem is likely to continue and worsen unless action is taken to stabilize groundwater reserves.

Wells that run dry can also threaten crop production. Groundwater depletion has long been viewed as one of the greatest threats to global irrigated agriculture, because wells supply nearly half of the water used for irrigation globally.

In areas where groundwater typically drains to rivers, falling groundwater levels can reverse this flow and cause rivers to leak into the subsurface. This affects the river’s ecology and reduces water supplies downstream. In the U.S., leaky streams are more common where groundwater withdrawal rates are high, highlighting how groundwater pumping can directly reduce the amount of water that flows underground into nearby rivers.

Groundwater declines can also cause land surfaces to sink. Land subsidence has increased flood risks in dozens of coastal cities worldwideincluding Jakarta, TokyoIstanbul, Mumbai, Auckland and the Tampa Bay area of Florida.

Farther from the coast, land subsidence can damage infrastructure. It poses a critical challenge in areas where groundwater levels have declined, including Tehran and Mexico City. In many cases, the main culprit is excessive groundwater pumping.

Finally, falling groundwater can cause seawater to move inland underground and contaminate coastal groundwater systems – a process known as seawater intrusion. When seawater intrudes, coastal aquifers can become too saline to use for drinking water without energy-intensive desalination.

How to replenish groundwater supplies

We also found places where groundwater levels are recovering. The strategies that communities used to replenish their groundwater sources included developing new alternative water supplies, such as local rivers; adopting policies to reduce demand for groundwater; and intentionally replenishing aquifers with surface water.

The town of El Dorado, Arkansas, saw its groundwater levels drop by roughly 200 feet (60 meters) from 1940 through 2000 as local industries pumped water from the aquifer. In 1999, a new policy established a pumping fee structure, giving businesses an incentive to find a new water supply. By 2005, a pipeline had been built to divert water from the Ouachita River to El Dorado. This new source reduced demand for groundwater, and groundwater levels have risen in the area since 2005.

In Bangkok, so many private wells were drilled for domestic, industrial or commercial purposes between 1980 and 2000 that groundwater pumping doubled and groundwater levels fell. Officials responded by quadrupling groundwater extraction fees between 2000 and 2006. Total groundwater pumping declined, and levels began to recover as users found other water sources.

In a valley near Tucson, Arizona, groundwater levels declined by 100 feet (30 meters) as withdrawals for irrigation increased after the 1940s. To help replenish the depleted groundwater, leaky ponds were constructed. These ponds are filled with water from the Colorado River that is moved hundreds of miles to the area via canals. As these ponds leak, they refill the depleted aquifer. Because of these leaky ponds, groundwater levels in the valley have risen by about 200 feet (60 meters) in places.

Our analysis shows how important it is to monitor groundwater levels in many locations. With groundwater levels declining in many places, communities and businesses that depend on it need accurate information about their water supplies so they can act in time to protect them.


Esper et al. 2024 in Nature communicartions earth & environment:

The IPCC’s reductive Common Era temperature history

Common Era temperature variability has been a prominent component in Intergovernmental Panel on Climate Change reports over the last several decades and was twice featured in their Summary for Policymakers. A single reconstruction of mean Northern Hemisphere temperature variability was first highlighted in the 2001 Summary for Policymakers, despite other estimates that existed at the time. Subsequent reports assessed many large-scale temperature reconstructions, but the entirety of Common Era temperature history in the most recent Sixth Assessment Report of the Intergovernmental Panel on Climate Change was restricted to a single estimate of mean annual global temperatures. We argue that this focus on a single reconstruction is an insufficient summary of our understanding of temperature variability over the Common Era. We provide a complementary perspective by offering an alternative assessment of the state of our understanding in high-resolution paleoclimatology for the Common Era and call for future reports to present a more accurate and comprehensive assessment of our knowledge about this important period of human and climate history.