The little ice age was a period of unusually cold temperature in many parts of the world that lasted from about the year 1350 until 1900CE. There were unusually harsh winters, and glaciers grew larger in many areas. Scientist have long wondered what caused the Little Ice Age. Several possible causes have been proposed.
First, the cooling may have been caused by disrupting of ocean currents. Before the Little Ice Age, there was a period of unusually warm weather during which glaciers melted. These melted glaciers sent a large amount of cold freshwater into the Gulf Stream, a large ocean current that strongly affects Earth's climate. Some scientists believe that this freshwater was enough to temporarily disrupt the Gulf Stream. Such a disruption could have caused the Little Ice Age.
Second, volcanic eruption could have caused the Little Ice Age. When volcanoes erupt, they send dark clouds of dust and sulfur gas into the atmosphere. These clouds, which can spread over great areas, block some sunlight from reaching Earth's surface. This can decrease the global temperatures. Scientists know of several volcanic eruption that took place during the Little Ice Age.
Third, substantial decreases in human populations may have contributed indirectly to the cooling of the climate. For a variety of reason(disease, warfare, social disruption), the human population just before the Little Ice Age and during the early part of it was lower than it had been in a long time. Forest trees started growing on fields that were no longer used for agriculture. Since trees absorb carbon dioxide, a greenhouse gas, they decrease the greenhouse effect that keeps Earth warm. With more forest trees carbon dioxide, earth became cooler.
Unfortunately，the arguments of the reading passage are a little out of date. Scientists now have new information that shows that none of the ideas the reading passage discusses could account for the Little Ice Age.
First，about the Gulf Stream.Scientists now know that disrupting the Gulf Stream would cause cooling only in Europe and North America，but the Little Ice Age also affected the Southern hemisphere，in places like New Zealand and Southern Africa for example.Since the disruption of the Gulf Stream cannot explain why these southern areas became colder，it cannot explain the Little Ice Age.
Second, the volcanoes theory.It’s true that if volcanic eruptions put enough dust into the atmosphere.the result can be a cooler climate.But large amounts of volcanic dust in the atmosphere would have also produced striking visual effect that people would have noticed at the time.For example.Dramatically colorful Sunsets or snow being grey or brown instead of white.But there are almost no reports of anything like that routinely happening during the Little Ice Age.So it seems that the volcanic eruptions during that period were simply not strong enough to release the large amounts of dust needed to lower global temperatures.
Third, about forests on farmland stopping the warming greenhouse effect by removing carbon dioxide.There just was not enough time for this effect to work.The human population grew back to previous levels fairly quickly，which meant that forests were soon being cut down
again to clear fields for the crops needed to feed the growing population.As a result，we know that the forests mentioned in the reading passage were not there long enough to cause the long—term global cooling of the climate.
Summarize the point made in the lecture ， being sure to explain how the cast doubt on specific points made in the reading passage.
In the reading passage, the author claims that the cause of the Little Ice Age was due to three main reasons. The lecturer, however, reputes the writer’s opinion one by one with strong arguments.
Firstly, the passage argues that the Gulf Stream formed in the previous warm period was responsible for the appearance of the unexpected Little Ice Age. Yet, the speaker argues that the so-called Gulf Stream only contributed to the cooling weather in Northern hemisphere while Little Ice Age took place all over the world. Thus, global Little Ice Age cannot be Next, according to the reading material, dust and sulfur gas caused by volcanic eruptions would block sunlight, and resulted in Little Ice Age. he lecturer, however, holds that volcanic eruptions should have led to other visual phenomena than cooling weather, like colorful sunsets or grey snow. But unfortunately none of them were reported. Once taken this into consideration, volcanic eruptions seems not strong enough to release the large amounts of dusts needed to lower global temperatures.
Last but not least, the writer states that the substantial decrease in human population may cause the unusual Little Ice Age. Again the speaker argues.