The sun's luminosity is stable and the earth is turning well. Why is there a periodic ice age?
The sun rises from the east to the west, and the four seasons change as usual. In our impressions, all natural alternations have a stable regularity. I never found which year did not come in winter or which year was not hot in summer.If the sun ’s luminescence is basically stable during its main sequence of star cycles, why do periodic glacial periods occur on Earth? That is, the northern and southern hemispheres are covered by large areas of ice. But the periodic glacial period is indeed true, And the sun is also very stable, so what's going on?
In the past 2.5 million years, the Earth has experienced more than 50 Great Ice Ages, each time having a profound impact on the Earth ’s climate. How do we predict the next Great Ice Age?
About 40 years ago, scientists realized that the ice age was caused by the eccentricity of the Earth's orbit and the precession of the rotation axis. But things are not so simple. Scientists are still trying to understand how the Earth's orbital oscillations interact with the climate systemEspecially greenhouse gas effects, thereby pushing the Earth into and out of the Ice Age.
In the last Ice Age, only 21,000 years ago, from the Pacific to the Atlantic, there were almost continuous glaciers on North America and the Asian continent. In the deepest part of the Hudson Bay, there are ice layers that are more than 3 meters thick.Extending south to today's New York and Cincinnati. Europe has two main ice sheets: the British ice sheet extends south to Norfolk, and the Scandinavian ice sheet extends from Norway to Ural, Russia.Mountains.
In the southern hemisphere, Patagonia, South Africa, South Australia, and New Zealand all have obvious ice sheets. At that time, most of the earth's water was locked in glaciers, which caused the global sea level to drop by 125 meters, higher than the height of the London Eye.It's about 10 meters lower. By contrast, if all the ice on Antarctica and Greenland melts today, sea levels will only rise by about 55 meters.
So biologists also say that humans originated in Africa, because at that time only humans near the equator were suitable for human survival, and after the end of the Ice Age, humans migrated to various places on the earth.
1941, Miludin Milankovich proposed that the swing of the Earth's orbit changed the distribution of solar insolation on the earth's surface and promoted the ice age cycle. He believes that solar radiation located 65 degrees north latitude south of the Arctic CircleThe amount is very important. Here, the sunshine can vary by up to 25%. When the sunshine decreases in summer, the average summer temperature will be slightly lower, and the ice layer in this area can be preserved and slowly accumulated, eventually forming an ice cap.
But it was not until 30 years later that three scientists tested this theory using long-term climate records that analyzed marine sediments. Jim Hayes used a combination of fossils to estimate the surface temperature of the past ocean. Nick ShakerHe calculated the changes in global ice volume in the past by measuring the oxygen isotopes calcium atoms with different numbers of neutrons in calcium carbide fossils in marine sediments. John Inbury used time series analysis to statistically compare ocean surface temperatures and global ice.And time and period of the Earth's orbit pattern.
In December 1976, they co-published a landmark climate science paper that showed changes in summer sunlight in the northern and southern hemispheres and changes in the eccentricity of the Earth's orbit, the intersection angles of the ecliptic and equatorial planes, and precessionThe eccentricity describes the shape of the Earth's orbit around the sun, ranging from approximately circular to elliptical, with a period of about 96,000 years; the yellow-red intersection angle is the inclination of the Earth's rotation axis relative to its orbital plane, and its period of change is about 41,000Precession refers to the precession rotation of the Earth's rotation axis and orbital path over time. The combined effect of these two components and eccentricity produces a period of approximately 21,000 years.
Researchers also found that these parameters have different effects in different places on the earth. The yellow-red intersection angle has a greater impact on high latitudes, and the orbital precession has a significant effect on the tropical season. For example, the orbital precessionRelated to the rise and fall of the Great Rift Valley Lakes in Africa, and may even have affected the evolution of our ancestors.
In addition to changes in Earth's orbit, what other factors?
Scientists are also aware of the limitations of the Institute, and for the time being, they have not fully understood the impact of the Earth ’s atmospheric factors and orbital changes on the Ice Age. In particular, scientists have realized that changes in the Earth ’s orbit may not have caused the Ice Age itself.The reason, but because the orbital changes dominate the Ice Age cycle.
Changes in sunlight due to changes in the Earth's orbit can push the planets into or out of the Ice Age through the planet's "atmospheric feedback" mechanism. For example, when solar radiation in summer decreases, some ice still exists after summer. These whiteOf ice reflects more sunlight, which lowers the temperature in the area further, causing more ice to accumulate and reflect more sunlight. Therefore, researchers understand the relative importance of ice caps, oceans, and atmospheric feedback.They found that greenhouse gases play an important role in controlling the climate. In particular, the carbon dioxide in the atmosphere must be low enough for the earth to start cooling before entering the ice age.
One view is that a small increase in greenhouse gases caused by agricultural expansion that began 8000 years ago actually delayed the arrival of the next ice age. More importantly, if we continue to emit greenhouse gases at the same rate, we mayWill delay the next ice age by at least 500,000 years.
If we just postpone the next Ice Age, we will still be in the Quaternary of the Earth. The Quaternary began about 2.6 million years ago and continues to this day. If we humans stop the Ice Age, humanity willBringing greater changes to the earth has truly started the anthropocene era. In summary, the next ice age is expected to wait a long time because humans are covering the earth with quilts.
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