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寻找细节的“历史汇率”耕地损失

在做研究的问题沙漠化(又名土地退化)我一直运行在相同的基本句子但是没有源或细节来支持或澄清:

“耕地损失估计有30到35次历史汇率。”

谁能帮我找到一个指定的源这个“历史汇率”?在历史上被测量的时间长度是什么?这些数据的地理范围是什么?

这句话没有一个特定的来源,谁能提供一个可靠的数据来源的引用是指(即荒漠化的长期记录)?

回答

这是一个奇怪的问题。我同意戈登的陌生人,没有上下文(和提及与同行评议的研究,或者至少,某种测量),很没有意义的。我做了一个谷歌搜索和检查与books.google.com的搜索一个来源,但一切回指UNCCD UNCCD,据我读他们的报告,没有那句话的解释或提供来源。(谷歌搜索图书)[1][报告列表][2]我经历了几个,没有运气。我确实发现:[![在这里输入图像描述][3]][3][源][4]:但问题是,他们比你使用不同的标准。森林可以允许创建新的耕地,这就是为什么他们表现出增加当UNCCD显示下降。如果你把这个图表和森林砍伐,你可能有一点接近你所要找的。在美国,(编辑)农田(不一定是耕地)有所下降,但由于改进技术,粮食产量增加了肥料和所有的好东西。江南登录网址app下载[图表][5][源][6]坏耕作方式会导致耕地流失比好方法快得多。 [Here's a good answer][7] on the dustbowl that you might find interesting and even early societies, thousands of years ago, they lost arable land cause there were processes that happened that they didn't understand, [explained more here][8]. Environmental effects, mostly tend to be cyclical and are probably harder to measure outside of human effects. California might have a big drought one year and have a great growing season the next. The droughts we experience don't make the land permanently not arable, just for 1 growing season. Floods - might have a bigger effect if they wash away good land but they can also have the opposite effect, depositing rich silts adding nutrients to the soil. Over long term, climate change can affect arable land, for example, 13,000 years ago / give or take, the Sahara was a rich forest with huge lakes (We know this by fossils that remain there) and that may be a cycle that comes and goes with every orbital tilt of the Earth. During the last ice age, much land was covered by ice, but lower sea levels left lots of rich valleys that are now covered by water. The story of Noah and Gilgamesh are thought to be based on the flooding of one such fertile valley, caused in part by the end of the ice age and rising water. So, at least from an environmental perspective, it's a complicated question with lots of moving parts. Hope that helps, though I'm not sure it does. I was curious about what you asked so I looked into it a bit. [1]: https://www.google.com/?gws_rd=ssl#q=Arable%20land%20loss%20is%20estimated%20to%20be%20at%2030%20to%2035%20times%20the%20historical%20rate&btnK=Google%20Search [2]: http://www.unccd.int/en/resources/publication/Pages/default.aspx [3]: http://i.stack.imgur.com/2zXhn.png [4]: http://www.landcommodities.com/farmland-supply-and-investment-fundamentals/ [5]: http://www.ers.usda.gov/media/1874727/mon-ag-outputs-and-inputs.png [6]: http://www.ers.usda.gov/data-products/charts-of-note.aspx [7]: //www.hoelymoley.com/questions/400/what-started-the-us-dust-bowl-of-the-1930s-and-could-it-happen-again [8]: //www.hoelymoley.com/questions/5134/did-the-neolithic-revolution-have-an-effect-on-the-earths-climate

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