The two RP hosts conducting the interview seemed to expect Dr. Kröpelin would tell the audience how dire the consequences of man-made global warming are on the Sahara Desert and planet overall.
They didn’t get what they bargained for.
Warming does not lead to desertification
Instead, in the interview, Dr. Kröpelin rejected in very clear terms man’s major climatic impact and that global warming is only negative.
Kröpelin told listeners that history is very clear: When the globe is cold, the deserts expand. And when the globe is warm, deserts become greener and far more fruitful.
Kröpelin is a leading expert
Kröpelin has been studying the Sahara for over 40 years, spending weeks and months each year on site gathering data a reconstructing past climates. Naturedescribed Kröpelin as “one of the most devoted Sahara explorers of our time.”
At about 9 minutes into the interview, he explains how the Sahara was massive in size during the last glacial period, and that about ten thousand years ago it greened up once temperatures shot up early in the Holocene.
When asked (10:15) if he worries that things in the Sahara “will get much worse” due to climate change, Kröpelin tells the host and audience: “First, that is a statement I 100% reject”, adding that localized desertification has more to do with the population growth at the edges of the desert and that the people who live there are cutting down trees and extracting water from the ground.
The Eocene was, on average, 4–15 °C warmer than today.
Atmospheric CO2 was very likely in the 450-600 ppm range.
Modern climate models would require 4,500 ppm CO2 to simulate the Eocene temperature range;
And/or a climate sensitivity of 4-8 °C per doubling;
And/or “that other climate forcings were stronger than previously assumed”.
They totally missed the most obvious reason why just about every effort to gin up a paleo example of CO2-driven climate change falls apart: Atmospheric CO2 is not a primary driver of climate change over geologic time. This wouldn’t mean that it isn’t a greenhouse gas or that it has no effect on temperature. It would simply mean that it was a relatively minor climate driver, like volcanic eruptions.
At some point over the past 30 years or so, the assumption that CO2 drives modern climate change has become a paradigm. And I think we have seen a rare failure in the application of the geologic principle of Uniformitarianism.
Uniformitarianism is often incorrectly cited as the reason geologists were slow to accept plate tectonics, the impact theory of the K-Pg extinction and why the hypotheses for a Younger Dryas impact and abiotic oil are generally unaccepted. However, Uniformitarianism may be why a CO2-driven climate paradigm appears to have come into wide acceptance, at least in academia.
Figure 3a. Marine pCO2 (foram boron δ11B, alkenone δ13C), atmospheric CO2 from plant stomata (green and yellow diamonds with red outlines), Mauna Loa instrumental CO2 (thick red line) and Cenozoic temperature change from benthic foram δ18O (light gray line).
by Alain Préat, 25 septembre 2019 in Science-Climat-Energie
Résumé : L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète (nb: première partie 1/2, ici).
Malgré un apport en oxygène lié aux cyanobactéries dès l’Archéen, ce ne se sont pas ces microorganismes qui sont à la base de la première grande ‘révolution’ de l’oxygène qui a eu lieu à la limite Archéen/Paléoprotérozoïque (il y a 2,5 milliards d’années) dans l’atmosphère, lors du Grand Evénement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique vers 2,5 milliards d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite (= FeS2). L’altération des séries riches en ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’Archéen sera remplacée par une atmosphère oxydante à la fin du Précambrien.
Abstract : Oxygen did not appear as abruptly as we thought on our planet.
Despite an oxygen supply related to cyanobacteria, since the Archean, it is not these microorganisms that are at the base of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (2.5 billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the of atmospheric oxygen concentration 2.5 billion years ago. These two main processes are related to the burial of organic matter and those of pyrite(= FeS2) The alteration of series with high contents of the two elements will then condition for nearly a billion of years the oxygen, sulfur and iron chemical composition of the oceans. The oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian.
by Alain Préat, 20 septembre 2019, in ScienceClimatEnergie
Résumé : L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète.
Malgré un apport en oxygène lié aux cyanobactéries dès l’Archéen, ce ne se sont pas ces micro-organismes qui sont à la base de la première grande ‘révolution’ de l’oxygène qui a eu lieu à la limite Archéen/Paléoprotérozoïque (il y a 2,5 milliards d’années) dans l’atmosphère, lors du Grand Evénement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique vers 2,5 milliards d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite (= FeS2). L’altération des séries riches en ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’Archéen sera remplacée par une atmosphère oxydante à la fin du Précambrien.
Abstract : Oxygen did not appear as abruptly as we thought on our planet.
Despite an oxygen supply related to cyanobacteria, since the Archean, it is not these microorganisms that are at the base of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (2.5 billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the of atmospheric oxygen concentration 2.5 billion years ago. These two main processes are related to the burial of organic matter and those of pyrite (= FeS2). The alteration of series with high contents of the two elements will then condition for nearly a billion of years the oxygen, sulfur and iron chemical composition of the oceans. The oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian.
Figure 2a( en haut). Stromatolithe columnaire, Néoprotérozoïque, (Formation SC1c in Préat et al. 2018), Bassin du Niari, République du Congo (Brazzaville), photo A. Préat, 2016.
Late in the prehistoric Silurian Period, around 420 million years ago, a devastating mass extinction event wiped 23 percent of all marine animals from the face of the planet.
For years, scientists struggled to connect a mechanism to this mass extinction, one of the 10 most dramatic ever recorded in Earth’s history. Now, researchers from Florida State University have confirmed that this event, referred to by scientists as the Lau/Kozlowskii extinction, was triggered by an all-too-familiar culprit: rapid and widespread depletion of oxygen in the global oceans.
A huge source of methane has been discovered deep beneath the surface of Earth, sitting between the upper mantle and lower oceanic crust. The discovery is important as it could provide an insight into the hydrothermal vents that may have helped the planet’s first life emerge. Researchers also argue it could be a source of hydrogen and methane on other planets in the solar system—”even those where liquid water is no longer present.”
The ‘abiotic’ methane—methane that is not formed with organic matter—was found locked inside rocks. Researchers from the Woods Hole Oceanographic Institution (WHOI), Massachusetts, took 160 samples from hydrothermal sites across the globe, including the Mid-Atlantic Ridge, Guaymas Basin, the East Pacific Rise and the Mid-Cayman Rise. After analyzing them with a laser-based microscope, they found that almost all contained pockets of methane.
In their study, published in the journal PNAS, the team says this could be the biggest source of abiotic methane in the world. This reservoir, they say, could account for more methane than was in Earth’s atmosphere before the onset of the industrial era.
The methane appears to have formed by reactions between trapped water and olivine, a group of rock-forming minerals found in the planet’s subsurface. When seawater moves through the deep ocean crust, it mixes with magma-hot olivine. When the mineral cools, the water is trapped inside and a chemical reaction takes place, leading to the formation of hydrogen and methane.
Traditionally, we think of methane—a potent greenhouse gas—as forming when organic material breaks down. When it is emitted into the atmosphere, it has a warming effect far greater than carbon dioxide, although it is far shorter-lived than the latter, disappearing after about a decade.
However, methane is also known to exist on the seafloor. It is released through deep-sea vents—geothermally heated fissures on Earth’s crust. In 2016, scientists with the Ocean Exploration Trust discovered over 500 methane spewing vents off the west coast of the U.S.
However, the source of the seafloor methane has remained something of a mystery. “Identifying an abiotic source of deep-sea methane has been a problem that we’ve been wrestling with for many years,” study author Jeffrey Seewald, a senior scientist at WHOI, said in a statement.
Lead author Frieder Klein added: “We were totally surprised to find this massive pool of abiotic methane in the oceanic crust and mantle. Here’s a source of chemical energy that’s being created by geology.”
Methane hydrates is a source of methane gas which is found in crystalline formation that look like ice and can be found in permafrost regions or under the sea in outer continental margins.
We are living in times of fundamental changes in the energy landscape, driven by uncertainty, unstable energy prices, disruptive technologies, geopolitical gambits and subsequent attempts for regulatory interventions. While governments and corporations are trying to adjust to the new landscape and guess the name of the game, they need reliable sources of power to make predictions and critical strategic decisions.
Historical & geopolitical context
The era of hydrocarbons does not seem to be over, but there might be some indications in the horizon. We like it or not, they will still account for the vast majority of the global energy mix by 2050, despite significant breakthroughs in renewables. Many new players come in the energy market with the elusive promise of additional and cheaper resources and the will to disrupt the game – and eventually make money out of it.
Furthermore, the growing tension between public policy and private initiatives has been boiling and has been more than just an understatement for decades. The under-investment that we observe now due to lower prices and risks could become chronic and the global output of energy resources could lead to secure supply deficit.
Gas is believed to gradually replace coal, which is a source of distress for some existing players. The world is facing a proliferation of Liquified Natural Gas (LNG) supplies that are already impacting gas markets and competing with pipeline gas. Some of the largest and most significant consuming nations are contemplating reform or unbundling, which could mean some take or pay contracts become stranded and an increasing oil price is likely to reinforce the price arbitrage between long-term and spot pricing.
There is undeniably a constant call for further investments in renewables, but lower oil, gas and coal prices and increased efficiency (or very effective lobbying) might slow this down. The global players do take into consideration the call for renewables (like solar and wind energy), either for publicity purposes or even because they do believe that this could be the future.
Location of sampled and inferred methane hydrate occurrences in oceanic sediment of outer continental margins and permafrost regions. Most of the recovered methane hydrate samples have been obtained during deep coring projects or shallow seabed coring operations. Most of the inferred methane hydrate occurrences are sites at which bottom simulating reflectors (BSRs) have been observed on available seismic profiles. The methane hydrate research drilling projects and expeditions reviewed in this report have also been highlighted on this map. (Map courtesy of Timothy S. Collett, USGS)
The fake geologic epoch known as the “Anthropocene” just won’t die… It’s like a zombie from a bad science fiction movie.
Despite being populated with activists like Naomi Oreskes, it has taken the AWG ten years to vote on what their conclusion will be and to start looking for evidence to support their conclusion… And the vote wasn’t unanimous.
Here’s where the Anthropocene dies…
Figure 4 from Finney & Edwards. “Workflow for approval and ratification of a Global Standard Stratotype Section and Point (GSSP) proposal. Extensive discussion and evaluation occurs at the level of the working group, subcommission, and International Commission on Stratigraphy (ICS) Bureau. If approved at these successive levels, a proposal is forwarded to the International Union of Geological Sciences (IUGS) for ratification. This process is also followed for other ICS decisions on standardization, such as approval of names of formal units, of revisions to the units, and to revision or replacement of GSSPs.”
Fossils of a large new predatory species in half-a-billion-year-old rocks have been uncovered from Kootenay National Park in the Canadian Rockies. This new species has rake-like claws and a pineapple-slice-shaped mouth at the front of an enormous head, and it sheds light on the diversity of the earliest relatives of insects, crabs, spiders, and their kin.
Reaching up to a foot in length, the new species, named Cambroraster falcatus, comes from the famous 506-million-year-old Burgess Shale. “Its size would have been even more impressive at the time it was alive, as most animals living during the Cambrian Period were smaller than your little finger,” said Joe Moysiuk, a graduate student based at the Royal Ontario Museum who led the study as part of his PhD research in Ecology & Evolutionary Biology at the University of Toronto. Cambroraster was a distant cousin of the iconic Anomalocaris, the top predator living in the seas at that time, but it seems to have been feeding in a radically different way,” continued Moysiuk.
The find—described today in the journal Current Biology—is the fourth Microraptor fossil to preserve stomach contents, but it’s the first to show that Microraptor ate lizards. Previous fossils captured it eating small mammals, fish, or birds. The specimen also reveals that, like some predatory birds today, Microraptor had a taste for swallowing lizards whole and head-first.
This fossil of the feathered dinosaur Microraptor also preserves the animal’s last meal: a lizard it seems to have swallowed whole and head first.
Volcanism, primarily ocean floor in nature, is the most feasible and plausible cause of recent alterations to the Bering Sea physical and biological systems, not climate change.
Since 2014, multiple changes to the Bering Sea’s physical and biological systems such as a rise in seawater temperature, sea ice melting, alteration of commercial fish migration patterns and the very sudden die-off of certain sea bird species have made front-page news.
Many scientists have been quick to attribute these supposedly ‘unnatural’ events to human-induced atmospheric warming or climate change without mentioning or giving due consideration to emissions from active volcanic features that circumvent the entire Bering Sea and populate its seafloor.
This immediate jump to a climate change cause and event effect relationship is especially difficult to understand knowing that frequently during the last five years we have been informed of yet another eruption from a Bering Sea area volcano located in either Russia, Alaska, or on the Bering seafloor.
So, let’s take a moment to review Bering Sea volcanic activity and its likely effect on the area’s physical and biological systems.
Higher reactivity could explain temperature drop before last ice age
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
From time to time, there have been long periods of cooling in Earth’s history. Temperatures had already fallen for more than ten million years before the last ice age began about 2.5 million years ago. At that time the northern hemisphere was covered with massive ice masses and glaciers. A geoscientific paradigm, widespread for over twenty years, explains this cooling with the formation of the large mountain ranges such as the Andes, the Himalayas and the Alps. As a result, more rock weathering has taken place, the paradigm suggests. This in turn removed more carbon dioxide (CO2) from the atmosphere, so that the ‘greenhouse effect’ decreased and the atmosphere cooled. This and other processes eventually led to the ‘ice Age’.
In a new study, Jeremy Caves-Rugenstein from ETH Zurich, Dan Ibarra from Stanford University and Friedhelm von Blanckenburg from the GFZ German Research Centre for Geosciences in Potsdam were able to show that this paradigm cannot be upheld. According to the paper, weathering was constant over the period under consideration. Instead, increased ‘reactivity’ of the land surface has led to a decrease in CO2 in the atmosphere, thus cooling the Earth. The researchers published the results in the journal Nature.
Geothermal heat flux can foment upper mantle temperature anomalies of 800–1000 °C, and these extreme heat intensities have been found to stretch across 500 km of central-east Greenland. This could result in “a significant contribution of ice melt to the ice-drainage system of Greenland” (Artemieva et al., 2019).
Evidence of more than 100,000 formerly or currently active volcanic vents permeate the Earth’s sea floor (Kelley, 2017).
Active volcanoes spew 380°C sulfuric acid and “metal-laden acidic fluids” into the bottom waters of the world ocean on a daily basis. In other words, literal ocean acidification is a natural phenomenon.
The carbon dioxide concentrations present in these acidic floods reach “astounding” levels, dwarfing the potential for us to even begin to appreciate the impact this explosive geothermal activity has on the Earth’s carbon cycle (Kelley, 2017).
THIS POST IS A CRITICAL EXAMINATION OF VARIOUS CLAIMS MADE BY CLIMATE SCIENCE ABOUT THE IMPACT OF CLIMATE CHANGE ON ANTARCTICA AND OF THE EVIDENCE FOR AGW CLAIMED TO BE FOUND IN DATA FROM ANTARCTICA.
IT IS BASED ON THE ANTARCTICA SECTION OF A LECTURE BY JAMES EDWARD KAMIS [LINK]
Antarctica is broken into two pieces. On the west is West Antarctica that constitutes 20% of Antarctica. The upper portion of West Antarctica forms a thumb. It’s called the Antarctic Peninsula. The remaining 80% of Antarctica is called East Antarctica. The right image shows a NASA graph that reflects ice melting on the entire continent from 1995 to 2015. It is here shown as a proxy for ice melting denominated as millimeters of sea level rise due to meltwater. Note that West Antarctica, inclusive of the Antarctic Peninsula, the 20% portion of the continent, accounts for all of the continent’s ice loss. East Antarctica, the much larger 80%, is actually gaining ice. This melt graph was created in 2015 by Dr. H. Jay Zwally is Chief Cryospheric Scientist at NASA’s Goddard Space Flight Center and Project Scientist for the Ice Cloud and Land Elevation Satellite.
The lopsided melt data raises this question: why is all the melt concentrated in 20% of the continent while the other 80% gains ice? The answer is found in the University of Washington 50-year average surface temperature map. It was generated in 2009 by Dr. Eric Steig – Earth and Space Sciences – University of Washington. It’s validity was hotly debated for many years. However, since that time, it has been proven correct by two more modern studies. NASA’s skin temperature map and British Antarctic Survey’s temperature map.
The surface temperature map that Dr. Steig made represents the temperature of the upper few meters of ice and sediment and does not reflect the temperature of the atmosphere…
by J.E. Kamis, May 25, 2016 in ClimateChangeDispatch
The most plausible scenario for southern Greenland’s surface ice melt is related to geologically induced heat flow and not atmospheric warming for various, well-established reasons. Based on research by the National Oceanic and Atmospheric Administration (NOAA) (see here), the top surface of southern Greenland’s ice sheet is currently melting at a high rate and therefore greatly reducing surface ice volume. They attribute this geographically localized melting effect to an unusually persistent and man-made atmospheric high pressure system (a so-called “Omega Block“) that has remained stationary above southern Greenland during the spring of 2016.
This non-moving high-pressure system has trapped a cell of very warm air above southern Greenland resulting in higher-than-normal surface ice melting rates and volumes. NOAA and the mainstream media are portraying this above-average melting as undeniable proof man-made global warming damaging our planet.
This portrayal is vastly misleading.
That’s because southern Greenland’s surface ice melt is more likely caused by natural, geologically induced heat flow from one of Earth’s largest Deep Ocean crustal plate junctures, the 10,000 mile long Mid-Atlantic Ridge (MAR). The Mid-Atlantic Ridge is “an immensely long mountain chain extending for about 10,000 miles (16,000 km) in a curving path from the Arctic Ocean to near the southern tip of Africa. The ridge is equidistant between the continents on either side of it. The mountains forming the ridge reach a width of 1,000 miles.”
The K-Pg extinction wiped out around 60% of the marine species around Antarctica, and 75% of species around the world. Victims of the extinction included the dinosaurs and the ammonites. It was caused by the impact of a 10 km asteroid on the Yucatán Peninsula, Mexico, and occurred during a time period when the Earth was experiencing environmental instability from a major volcanic episode. Rapid climate change, global darkness, and the collapse of food chains affected life all over the globe.
The K-Pg extinction fundamentally changed the evolutionary history of life on Earth. Most groups of animals that dominate modern ecosystems today, such as mammals, can trace the roots of their current success back to the aftermath of this extinction event.
A team of scientists from British Antarctic Survey, the University of New Mexico and the Geological Survey of Denmark & Greenland show that in Antarctica, for over 320,000 years after the extinction, only burrowing clams and snails dominated the Antarctic sea floor environment. It then took up to one million years for the number of species to recover to pre-extinction levels.
A team of scientists have given a fresh insight into what may have driven the “Cambrian Explosion” — a period of rapid expansion of different forms of animal life that occurred over 500 million years ago.
While a number of theories have been put forward to explain this landmark period, the most credible is that it was fuelled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.
The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics.
During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism — chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.
This, the team calculated, led to an increase in atmospheric CO2and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.
One researcher at the University of Tokyo is in hot pursuit of dinosaurs, tracking extinct species around ancient Earth. Identifying the movements of extinct species from millions of years ago can provide insights into ancient migration routes, interaction between species, and the movement of continents.
“If we find fossils on different continents from closely related species, then we can guess that at some point there must have been a connection between those continents,” said Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo.
A map of life – biogeography
Previous studies in biogeography — the geographic distribution of plants and animals — had not considered the evolutionary relationships between ancient species. The new method that Kubo designed, called biogeographical network analysis, converts evolutionary relationships into geographical relationships.
By combining data from fossils and models of the ancient Earth, researchers can map where ancient species may have migrated. This method, called biogeographical network analysis, converts evolutionary relationships between species into geographical relationships. This method was used in research by Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo. Credit Caitlin Devor, The University of Tokyo, CC-BY Usage Restrictions Image by Caitlin Devor, The University of Tokyo, CC-BY
Assessing human impacts on climate and biodiversity requires an understanding of the relationship between the concentration of carbon dioxide (CO2) in the Earth’s atmosphere and global temperature (T). Here I explore this relationship empirically using comprehensive, recently-compiled databases of stable-isotope proxies from the Phanerozoic Eon (~540 to 0 years before the present) and through complementary modeling using the atmospheric absorption/transmittance code MODTRAN. Atmospheric CO2 concentration is correlated weakly but negatively with linearly-detrended T proxies over the last 425 million years.
Mercury found in ancient rock around the world supports theory that eruptions caused ‘Great Dying’ 252 million years ago.
Researchers say mercury buried in ancient rock provides the strongest evidence yet that volcanoes caused the biggest mass extinction in the history of the Earth.
The extinction 252 million years ago was so dramatic and widespread that scientists call it “the Great Dying.” The catastrophe killed off more than 95 percent of life on Earth over the course of hundreds of thousands of years.
Paleontologists with the University of Cincinnati and the China University of Geosciences said they found a spike in mercury in the geologic record at nearly a dozen sites around the world, which provides persuasive evidence that volcanic eruptions were to blame for this global cataclysm.
The study was published this month in the journal Nature Communications.
The eruptions ignited vast deposits of coal, releasing mercury vapor high into the atmosphere. Eventually, it rained down into the marine sediment around the planet, creating an elemental signature of a catastrophe that would herald the age of dinosaurs.
“Volcanic activities, including emissions of volcanic gases and combustion of organic matter, released abundant mercury to the surface of the Earth,” said lead author Jun Shen, an associate professor at the China University of Geosciences.
It is thought that the Northern Hemisphere experienced only ephemeral glaciations from the Late Eocene to the Early Pliocene epochs (about 38 to 4 million years ago), and that the onset of extensive glaciations did not occur until about 3 million years ago. Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere-ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth’s orbit.
Over the last 540 million years, the Earth has weathered three major ice ages — periods during which global temperatures plummeted, producing extensive ice sheets and glaciers that have stretched beyond the polar caps.
Now scientists at MIT, the University of California at Santa Barbara, and the University of California at Berkeley have identified the likely trigger for these ice ages.
In a study published in Science, the team reports that each of the last three major ice ages were preceded by tropical “arc-continent collisions” — tectonic pileups that occurred near the Earth’s equator, in which oceanic plates rode up over continental plates, exposing tens of thousands of kilometers of oceanic rock to a tropical environment.
The scientists say that the heat and humidity of the tropics likely triggered a chemical reaction between the rocks and the atmosphere. Specifically, the rocks’ calcium and magnesium reacted with atmospheric carbon dioxide, pulling the gas out of the atmosphere and permanently sequestering it in the form of carbonates such as limestone.
Over time, the researchers say, this weathering process, occurring over millions of square kilometers, could pull enough carbon dioxide out of the atmosphere to cool temperatures globally and ultimately set off an ice age.
by James Kennett et al., March 13, 2019 in CO2Coalition
When UC Santa Barbara geology professor emeritus James Kennett and colleagues set out years ago to examine signs of a major cosmic impact that occurred toward the end of the Pleistocene epoch, little did they know just how far-reaching the projected climatic effect would be.
“It’s much more extreme than I ever thought when I started this work,” Kennett noted. “The more work that has been done, the more extreme it seems.”
He’s talking about the Younger Dryas Impact Hypothesis, which postulates that a fragmented comet slammed into the Earth close to 12,800 years ago, causing rapid climatic changes, megafaunal extinctions, sudden human population decrease and cultural shifts and widespread wildfires (biomass burning). The hypothesis suggests a possible triggering mechanism for the abrupt changes in climate at that time, in particular a rapid cooling in the Northern Hemisphere, called the Younger Dryas, amid a general global trend of natural warming and ice sheet melting evidenced by changes in the fossil and sediment record.
During the Mid-Holocene, when CO2 concentrations were stable and low (270 ppm), Antarctica’s massive Ross Ice Shelf naturally collapsed, adding the meltwater equivalent of 3-4 meters to sea levels.
Because CO2 concentrations changed very modestly during the pre-industrial Holocene (approximately ~25 ppm in 10,000 years), climate models that are predicated on the assumption that CO2 concentration changes drive ocean temperatures, ice sheet melt, and sea level rise necessarily simulate a very stable Holocene climate.
In contrast, changes in ocean temperatures, ice sheet melt, and sea level rise rates were far more abrupt and variable during the Holocene than during the last 100 years.
Modern ocean changes are barely detectable in the context of natural variability