Another important push was the onset of the Little Ice Age, a climatic phenomenon that led to cooler temperatures in the Northern Hemisphere.

另一个重要的推动因素是小冰期的开始，这一气候现象导致北半球气温下降。

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The formation of LMLS is a specific phenomenon during the process of climatic drought, and is one of the direct causes of vegetation pattern evolution.

土壤干层的形成是气候干旱化过程中必然出现的现象，它是导致植被演替的直接原因之一。

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The causes for the occurrence of this phenomenon are the influences of the sea-level rise and climatic change in the Mid Cretaceous.

该现象发生的原因是白垩纪中期的海平面上升和气候变化的影响。

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So while the climatic phenomenon may make a pandemic more likely, they say, it is not sufficient on its own - and may not be necessary either.

BBC: La Nina 'linked' to flu pandemics