Weather News: What was the last ice age like and can it happen again? 31/08/2022


After talking about the scorching heat and drought all summer, Météo Villes invites you to dive back into the last ice age the Earth experienced. Could long-lasting global cooling happen again? 11,700 years ago: the last ice age Thanks to paleoclimatology, man has been able to reliably reconstruct the Earth’s climate during the last hundreds of thousands of years. Thus, the researchers found that our planet undergoes a cycle of alternation between long glacial periods and shorter periods of marked warming (or interglacials). We are also during one of them. The last glaciation began 115,000 years ago and ended 11,700 years ago, an eternity on a human scale but a very short period on the scale of our planet at 4.5 billion years. Evolution of temperatures on Earth since the year -400,000- via It is generally accepted that it is the changes in the Earth’s orbit that generate the different cycles of glaciation and warming (Milankovitch cycles). A vicious cycle follows with a net increase or decrease of CO2, a powerful greenhouse gas, with a warming or cooling of the global climate. More specifically, we note on the left of the graph below that temperatures were 9°C below current values ​​at the peak of the last ice age, about 21,000 years ago. Suffice it to say that the weather was absolutely not the same. Evolution of CO2 levels and temperature on Earth from -450,000 years ago to the present day – through energy materials During periods of glaciation, it is the northern hemisphere of the planet that cools most notably. The explanation is simple: the northern part of the globe contains much more land than its southern part. However, cold accumulates and rises much more easily over continents than over oceans. Thus, at the height of the last ice age (21,000 years ago), ice covered all of northern Europe, as well as all of Canada and the northern United States. Part of South America was also frozen in ice. Ice extents on Earth 21,000 years ago at the height of the last ice age – via If we focus on Europe, we see that its entire northern part was covered by ice 21,000 years ago. Much of the United Kingdom, all of Scandinavia, all the regions bordering the Baltic Sea and even northeastern Germany were vast expanses of ice. In France, the Alpine glaciers were infinitely more extensive than today and all the valleys as far as Grenoble were covered with ice! Ice extents in Europe 21,000 years ago at the height of the last ice age – via Wikipedia Let’s not forget that man appeared on Earth a few million years ago (about 2.7 million for Homo habilis and 1.8 million for Homo erectus). Therefore, it survived several glaciation cycles. During the last ice age, it was Neanderthal man who had to adapt, migrating to caves and using fire to protect himself from the harshest cold. As nature has it right, our ancestors also developed a larger hair system during colder periods. Neanderthal man survived several ice ages – via Medieval minimum: a false ice age The medieval minimum is often called the “little ice age”. Indeed, global temperatures fell during the Middle Ages, starting in the early 1300s. Real warming would not be seen until the mid-19th century. However, this period of recent history has absolutely nothing to do with a glaciation. In the graph below we note that temperatures have only dropped by 1°C globally, a far cry from the 7-9°C drop caused by the actual ice ages! Curve of temperatures between the end of the last glaciation and the present – via In the era of time Studies have observed very important deposits of sulfates and glass microparticles in ice cores of the poles. They would have been formed in 1258 or 1259 and would be linked to a large volcanic eruption. The cause will be the volcanic eruption of 1257 on the island of Lombok in Indonesia. It would have thrown many particles into the stratosphere, reflecting more of the solar radiation back into space, contributing to gradual cooling. Other massive eruptions would have sustained the phenomenon in the following decades, although there are still some gray areas about the exact causes of this long-lasting cooling. The “little ice age” made life very difficult during the Middle Ages – P.Bruegel Can a new ice age occur? Climate skeptics often argue that current global warming is just a natural cycle. Don’t get the scale wrong! Past warming cycles spanned thousands of years, with very slow increases in CO2 levels in Earth’s atmosphere. With human activity, CO2 levels have exploded in record time, increasing by 50% in less than 200 years! Today we reach more than 418 ppm of CO2 in the air, while the record more than 300,000 years ago was 300 ppm. And rates continue to soar at unprecedented speeds! The role of man is undeniable. Rate of CO2 on Earth from the year -800,000 to the present – via NASA/NOAA You only have to look at the evolution of global temperatures since the beginning of the millennium to realize the leak since the beginning of the industrial revolution. While the increases and decreases in temperature occurred slowly over thousands of years, the curve takes off in just a few decades! And since there is always more CO2 in the air, the rise in global temperatures is not about to stop… Global Temperature Evolution from Year 0 to Present – via Ed Hawkins Si we refer to the Milankovitch cycles mentioned at the beginning of this article, the next periods favorable to a glaciation will take place between 40,000 and 60,000 years. But several studies indicate that historical levels of CO2 in the atmosphere could delay future glaciation (some studies say 100,000 years). Interglacial periods (like the current one) are always followed by glaciations. But what will be left of man in several tens of thousands of years? Projection of global temperature rise for the year 2100 – via AFP While the most pessimistic scenarios predict a temperature rise of 7 °C by the year 2100, we should not count on another glaciation to solve the our global warming problems. It is not certain that the man will still be there during the next one. In addition, there are still many unknowns: in a few centuries man will run out of oil, gas or coal. What will happen to our CO2 emissions? How will the Earth absorb the excess? In any case, each of us is suffering the effects of climate change today when our generation will not be here for many millennia during the next ice age.
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