![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
. | ![]() |
. |
![]() by Staff Writers Geneva, Switzerland (SPX) Sep 14, 2018
56 million years ago, the Earth experienced an exceptional episode of global warming. In a very short time on a geological scale, within 10 to 20'000 years, the average temperature increased by 5 to 8 degrees, only returning to its original level a few hundred thousand years later. Based on the analysis of sediments from the southern slope of the Pyrenees, researchers from the University of Geneva (UNIGE) measured the impact of this warming on river floods and the surrounding landscapes: the amplitude of floods increased by a factor of eight - and sometimes even by a factor of 14 -, and vegetated landscapes may have been replaced by arid pebbly plains. Their disturbing conclusions, to be discovered in Scientific Reports, show that the consequences of such global warming may have been much greater than predicted by current climate models. "The method we relied on to analyse this global warming is directly inspired by cell signaling in systems biology, where researchers analyse the response of cells to external stimuli and the ensuing signal transmission," explains Sebastien Castelltort, professor in the Department of Earth Sciences at the UNIGE Faculty of Sciences, and leader of the study, in collaboration with researchers from the universities of Lausanne, Utrecht, Western Washington and Austin. "We are interested in how a system, in this case the hydrologic cycle through the behavior of rivers, reacts to an external signal, here the global warming." This project focused on an extreme climatic case that was well known to scientists: a warming of 5 to 8 degrees that occurred 56 million years ago, between the Paleocene and the Eocene epochs, also known by the acronym PETM (Palaeocene-Eocene Thermal Maximum). Named Earth Surface Signaling System (ESSS) this project is supported by the Swiss National Science Foundation (SNSF).
Palm trees at polar latitudes Geologists use this type of observation as true "paleothermometres", which in this case show a rise in surface water temperature that has reached almost 36 degrees in places, a lethal temperature for many organisms. Several phenomena are cited as possible causes for this global warming, from the intense volcanic activity in several areas of the globe at this period, to the destabilization of methane hydrates, these methane "ice cubes" that only remain stable under certain pressure and temperature conditions, and which by degassing would have released their greenhouse gas. But although the event is known and its causes have been extensively explored, what about the consequences? "The question is important because there is an obvious analogy with the current global warming. There are lessons to be learned from this event, even more so as the rise in temperatures we are currently witnessing seems to be much faster," Sebastien Castelltort emphasizes.
Pebbles that reveal the history of rivers Step by step, thanks to the direct relationship between the size of the pebbles and the slope of the rivers, researchers were thus able to calculate their flow velocity and discharge. They have therefore unveiled the whole history of these rivers, and that of the spectacular changes that have affected them. 56 million years ago, the Pyrenees were being formed and their foothills were traversed by small isolated channels in a flood plain where they deposited very fertile alluvium, promoting the development of vegetation whose roots would anchor the soil. Leaving the Pyrenean piedmont, these small rivers then headed west into the Atlantic which was then only about thirty kilometres away.
The landscape changed completely During the PETM, rivers constantly changed course, they no longer adapted to increased discharge by incising their bed but instead they widened sometimes dramatically, from 15 to 160 meters wide in the most extreme case. Instead of being trapped in the floodplains, the alluvium was transferred directly towards the ocean, and the vegetation seemed to disappear. The landscape turned into arid extensive gravel plains, crossed by ephemeral and torrential rivers.
Far greater risks than expected "But our study shows that there are thresholds, non-linear evolutions that go beyond this ratio. With a ratio of 14 for flood magnitude, we face effects that we do not understand, which can perhaps be explained by local factors, but also by global factors that are not yet incorporated into current climate models. Our study proves that the risks associated with global warming may be far greater than we generally think," concludes Sebastien Castelltort.
![]() ![]() Prehistoric changes in vegetation help predict future of Earth's ecosystems Tucson AZ (SPX) Sep 11, 2018 As the last ice age came to an end and the planet warmed, the Earth's vegetation changed dramatically, reports a University of Arizona-led international research team. The current warming from climate change may drive an equally dramatic change in vegetation within the next 100 to 150 years unless greenhouse-gas emissions are reduced, the team wrote. "We found that ecosystems all over the globe experienced big changes," said Connor Nolan, a doctoral candidate in the UA Department of Geoscien ... read more
![]() |
|
The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us. |