America colonisation ‘cooled E |
送交者: 大马里昱 2019月02月01日17:00:59 于 [世界军事论坛] 发送悄悄话 |
回 答: 明朝灭亡是欧洲人占领美洲害的,因为农耕地都变回森林了 由 大马里昱 于 2019-02-01 16:57:09 |
America colonisation ‘cooled Earth's climate’ By Jonathan Amos BBC Science Correspondent 31 January 2019 Share this with Facebook Share this with WhatsApp Share this with Messenger Share this with Twitter Share Media captionMark Maslin and Chris Brierley: "A genocide-generated drop in carbon dioxide" Colonisation of the Americas at the end of the 15th Century killed so many people, it disturbed Earth's climate. That's the conclusion of scientists from University College London, UK. The team says the disruption that followed European settlement led to a huge swathe of abandoned agricultural land being reclaimed by fast-growing trees and other vegetation. This pulled down enough carbon dioxide (CO₂) from the atmosphere to eventually chill the planet. It's a cooling period often referred to in the history books as the "Little Ice Age" - a time when winters in Europe would see the Thames in London regularly freeze over. "The Great Dying of the Indigenous Peoples of the Americas led to the abandonment of enough cleared land that the resulting terrestrial carbon uptake had a detectable impact on both atmospheric CO₂ and global surface air temperatures," Alexander Koch and colleagues write in their paper published in Quaternary Science Reviews. Welcome to the Meghalayan Age New temperature 'starting point' sought Image copyright Getty Images Image caption Cool times: A depiction of a 17th Century Frost Fair at Temple Stairs on London's Thames River What does the study show? The team reviewed all the population data it could find on how many people were living in the Americas prior to first contact with Europeans in 1492. It then assessed how the numbers changed in following decades as the continents were ravaged by introduced disease (smallpox, measles, etc), warfare, slavery and societal collapse. It's the UCL group's estimate that 60 million people were living across the Americas at the end of the 15th Century (about 10% of the world's total population), and that this was reduced to just five or six million within a hundred years. The scientists calculated how much land previously cultivated by indigenous civilisations would have fallen into disuse, and what the impact would be if this ground was then repossessed by forest and savannah. The area is in the order of 56 million hectares, close in size to a modern country like France. This scale of regrowth is figured to have drawn down sufficient CO₂ that the concentration of the gas in the atmosphere eventually fell by 7-10ppm (that is 7-10 molecules of CO₂ in every one million molecules in the air). "To put that in the modern context - we basically burn (fossil fuels) and produce about 3ppm per year. So, we're talking a large amount of carbon that's being sucked out of the atmosphere," explained co-author Prof Mark Maslin. "There is a marked cooling around that time (1500s/1600s) which is called the Little Ice Age, and what's interesting is that we can see natural processes giving a little bit of cooling, but actually to get the full cooling - double the natural processes - you have to have this genocide-generated drop in CO₂." Image copyright Heidi Roop/NSF Image caption The fall in global carbon dioxide levels is recorded in the air bubbles trapped in ice cores Where's the support for the connection? The drop in CO₂ at the time of the Great Dying is evident in the ice core records from Antarctica. Air bubbles trapped in these frozen samples show a fall in their concentration of carbon dioxide. The atomic composition of the gas also suggests strongly that the decline is being driven by land processes somewhere on Earth. In addition, the UCL team says the story fits with the records of charcoal and pollen deposits in the Americas. These show the sort of perturbation expected from a decline in the use of fire to manage land, and a big grow-back of natural vegetation. Ed Hawkins, professor of climate science at Reading University, was not inv |
|
|
实用资讯 | |
|
|
一周点击热帖 | 更多>> |
一周回复热帖 |
历史上的今天:回复热帖 |
2018: | 用碳纤维做炮管能行?你可能想不到中国 | |
2018: | 英媒:梵蒂冈谴责香港前主教挑拨中梵关 | |
2017: | 发丝千分之一,中国自主研发光刻机量产 | |
2017: | 你可能喜欢川普, 但他打破惯例没给中国 | |
2016: | 国防大学金一南教授《台湾问题与国家安 | |
2016: | Shaolin monk KO world Taekwondo cham | |
2015: | 外交官忆70年代暗战:中国驻联合国人员 | |
2015: | 转几段台湾中研院院士陈永发几段论国共 | |
2014: | 我军苏-30年初一东海与外国军机机动“较 | |
2014: | 媒体:金正恩将中朝边界称为“战线”被 | |