When scientists and scholars discuss , or the demise of , or the , some will always attribute such events to climate change as they deflect responsibility from humans. Climate change has probably never been the ultimate cause for such events. The ultimate cause was probably always humans, and everything else was a proximate cause, at most. In the past several hundred years, there are clear instances when deforestation and sheep grazing quickly turned moist forests and/or , particularly in the kinds of temperate regions where the first civilizations arose. When scientists have investigated and reconstructed the dynamics that led to the collapse of , the , or the Anasazi, the story was always the same. Human civilizations altered the ecosystems, usually via deforestation and agriculture, which made them lose their resilience, and a drought did them in. Those urban areas were permanently abandoned. That civilization-collapse dynamic is like the hypothesis for why mass extinctions have punctuated the eon of complex life: those multi-tiered energy systems .
After newly exposed forest soils have produced a few crops, the yield will decline due to nutrient depletion. When the croplands receive less precipitation, yields drop. When soils wash away due to erosion, crop yields in those eroded soils will decline. Those effects reduce the EROI and surplus energy of farming those lands. When cropland is abandoned due to aridity, nutrient depletion, and erosion, and lands farther from Rome were conquered, deforested, and farmed, it took more energy to transport those crops to Rome than with farms closer to Rome. That also depressed the EROI and surplus energy. When harbors silted up and needed dredging, or were eventually abandoned and a port was built farther away, that also reduced the EROI and surplus energy of Rome-bound food. When food was used to feed soldiers who traveled increasingly vast distances to conquer and plunder peoples and their lands, those would be lower-EROI ventures than conquests closer to Rome. That dynamic has also been called in academic parlance, but in scientific terms, it is really just sucking the dregs of low-EROI resources after high-EROI energy sources have been depleted. Rome’s decline was really just another resource-depletion dynamic. Humanity’s first one was , and Rome only experienced what , , , , and numerous other early civilizations already suffered. Rome just did it on an unprecedented scale.
Build a model from designs you can find on the internet; determine what you are going to measure (rate of temp increase perhaps), then optimise or at least determine the effect of changing various variables (area, number of tubes, paint colour (gloss vs. matt), glass thickness (one sheet, two sheets etc). You should be able to hypothesise what the changes will do to the measured variable. Are there any mathematical relationships? Are any unexpected? Watch that your controlled variables (eg sunlight) really is controlled.
This chapter will provide a somewhat detailed review of the Cryogenian Ice Age and its aftermath, including some of the hypotheses regarding it, evidence for it, and its outcomes, as the eon of complex life arose after it. The ran from about 850 mya to 635 mya. This review will sketch the complex interactions of life and geophysical processes, and the increasingly multidisciplinary methods being used to investigate such events, which are yielding new and important insights.
When investigating how ice ages begin and end, and feedbacks are considered. A positive feedback will accentuate a dynamic and a negative feedback will mute it. In the 1970s, and the author of today’s , , , which posits that Earth has provided feedbacks that maintain environmental . Under that hypothesis, environmental variables such as atmospheric and levels, levels, and Earth’s surface temperature have been kept relatively constant by a combination of geophysical, geochemical, and life processes, which have maintained Earth’s inhabitability. The homeostatic dynamics were mainly negative feedbacks. If positive feedbacks dominate, then “runaway” conditions happen. In astrophysics, are responsible for a wide range of phenomena. A runaway greenhouse effect may be responsible for . Climate scientists today are concerned that burning the hydrocarbons that fuel the industrial age . Mass extinctions are the result of Earth's becoming largely uninhabitable by the organisms existing during the extinction event. The ecosystems then collapse Mass extinction specialist recently proposed his as a direct challenge to the Gaia hypothesis.
When historians debated the causes of Rome's decline and fall, for instance, they were merely debating proximate causes, which was understandable, as the science of energy did not yet exist when . Once scientists began to study the issue, running out of energy became seen as the ultimate cause, even though scientists still argue over environmental causes, for instance, but what some seem to miss in their arguments is that they are all just ways of saying that the civilization ran out of energy, whether humans contributed to the environmental failure (and declining and surplus energy) or not.
In an event that favors the hypotheses of climate-change advocates, there was a dip in global temperatures , which lasted for a few centuries. It was probably caused by remnants of the North American ice sheets melting and the resultant flush of freshwater into the North Atlantic. It was a less severe event than the , but it still caused epic droughts around the world. Some scientists think that the uncertainty caused by those cooling events helped spur agriculture, to enhance food security. Climate change from that event could be why Çatal Höyük was abandoned, and Tell Abu Hureyra survived the event, to only be abandoned several centuries later when another major dip in global temperatures occurred.
The culture’s killing implements abruptly appeared in the archeological record and disappeared just as fast, after the easily killable megafauna went extinct. Today’s North American megafauna are , not North American megafauna that learned to avoid humans. Bison are the only significant exception, although they came from Asia, too, and explaining their survival remains a minor curiosity, but is about the only circumstance not neatly aligned with the overkill scenario. The “” paper concluded that although the South American extinction was the greatest of all, it is the most poorly investigated and that the overkill hypothesis cannot yet be attached to South American extinctions. That may be a prudent position for a specialist who pronounces judgment only when all the evidence is in, but I will be among the most surprised people on Earth if the pattern of 50 thousand years did not continue there, especially since it had no ice sheets. There can be no more pertinent example than comparing Africa to South America. They inhabited the same latitudes and have similar climates, separated by the Atlantic Ocean. Africa was the home of humanity, where its animals had millions of years to adapt to the human presence, and Africa only lost about 10% of its megafauna (probably to human hunters with their advanced weaponry) while South America lost nearly all of its megafauna, and quickly. Climate change did it? How could it have even contributed?
Scientists are unanimous that the Western Hemisphere’s indigenous peoples primarily came from East Asia, but there has been a cottage industry for centuries proposing other ideas. When Thomas Jefferson sent the expedition to North America’s west coast in 1804 to , they were alerted to find the lost tribes of Israel. But genetic, anatomical, archeological, and other evidence has long since settled the issue of where American Indians came from, and by far the leading hypothesis is that humans migrated to North and South America beginning about 15 kya, and there may have been a migration along the Pacific coastline, which continued the . As the , a corridor between them formed and humans walked to North America about 11 kya. Those arrivals founded the . The sudden disappearance of virtually all the megafauna of North and South America followed those humans, particularly those that came by land and spread. That situation is where the original “” label was used.
From about 32 kya to 22 kya, prevailed in Europe. That culture produced the and art such as the . By 20 kya, . But as far as human expansion is concerned, the Gravettian (and related cultures) are most notorious as mammoth hunters extraordinaire for those that lived on the near the ice sheets. To , they could not swim to Sahul, but flourished everywhere else they could get to. At , they were the ultimate hunter-gatherer kill. Also, near the ice sheets, meat could be stored in the ground. Cro-Magnons did just that, and that “freezer” full of meat led to the first seasonally sedentary humans. It long predated the Domestication Revolution when people could be sedentary year-round, but while the megafauna lasted, the first signs of what came later appeared as Cro-Magnons created villages around frozen mammoth meat. Gravettians hunted along migration routes and set traps and ambushes for mammoths. For thousands of years, mammoths were the primary focus of Gravettian hunters, and many scientists believe that humans at least . Gravettians probably used the bow and arrow, and using poisoned arrows on mammoths would have been child’s play, not a hazardous undertaking. They also tended to focus on the easy meat: the young, relatively defenseless, tender mammoths. Killing the offspring alone would have driven the slowly reproducing mammoths to extinction, and as the interglacial period began around 15 kya, there would have been new pressures on mammoths. One of them was that fewer mammoths meant that they were not terraforming their environments like they used to, and the warming climate probably reduced their range. For a mammoth facing humans, there was literally no place to hide (except maybe in the living room), and there is little reason to think that hunters would have eased up when mammoth numbers dwindled. If anything, their efforts would have to get the last ones, as they competed and fought over the final mammoths. In one lifetime or even several, the changes would have been barely noticeable, if at all. There was simply no way out for mammoths, and they went extinct south of the European ice sheets under the ministrations of Cro-Magnon hunters. More evidence of their fate is some mammoths surviving in refugia: islands where humans did not arrive until thousands of years later. mammoths survived on in the chain off of Alaska until less than six kya, and went extinct when humans arrived. Several hundred apparently full-sized mammoths survived on near Siberia and went extinct less than five kya, when humans arrived. In today's France and Spain, Gravettians also semi-settled along the migration routes of reindeer and red deer. From Spain across Europe, into today's Russia, Gravettians hunted migrating herds, and not only the mammoth was driven to extinction, but also the wooly rhino, the Irish elk, the musk ox, and steppe bison were driven to extinction as the ice sheets retreated. Neanderthals had been ambush hunting in similar fashion, and those animals, like the African megafauna, grew wary of humans, and killing those animals probably took planning and guile.