Argument47 [OB小组]_第5次作业_6th世纪地球变冷因为火山爆发？

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TOPIC: ARGUMENT47 - Scientists studying historical weather patterns have discovered that in the mid-sixth century, Earth suddenly became significantly cooler. Although few historical records survive from that time, some accounts found both in Asia and Europe mention a dimming of the sun and extremely cold temperatures. Either a huge volcanic eruption or a large meteorite colliding with Earth could have created a large dust cloud throughout Earth's atmosphere that would have been capable of blocking enough sunlight to lower global temperatures significantly. A large meteorite collision, however, would probably create a sudden bright flash of light, and no extant historical records of the time mention such a flash. Some surviving Asian historical records of the time, however, mention a loud boom that would be consistent with a volcanic eruption. Therefore, the cooling was probably caused by a volcanic eruption.
WORDS: 574          TIME: 00:30:00+15:00          DATE: 2007-7-19 15:09:56

In this argument, the arguer states that the sudden cooling period in the mid-sixth century resulted from the lesser heat from the sun which appears dimming in some accounts then. S/he believes such phenomenon was caused by either the collision of a large meteorite with Earth or a huge volcanic eruption, both of which are able to create a large dust to block the sunlight. Since there are no extant historical records of a flash of collision but some Asian records of a loud boom, the arguer thus thinks it was the volcanic eruption that caused the cooling. His/her argument sounds logic. However, after close scrutiny, it suffers from several critical flaws.

First of all, the arguer made the fallacy of “A and B happen at the same time, A must be the reason of B". Though the dimming of the sun and the cooling appeared in the same period, such cooling does not necessarily be caused by the dimming of the sun. On the one hand, it is quite possible that in the mid-sixth century, the earth had just stepped into the glacial period when the global temperature fell naturally. Or such decrease of temperature was related to the less solar activities which was nothing to do with the brightness of the sun. Or, it might result from the decrease of content of "green house effect" gases which can hold the heat reflected by the surfaces of the earth. On the other hand, the dimming of the sun could be local occurrences in parts of Asia and Europe, in that case, such seeming phenomenon were not able to explain the decrease of temperature worldwide. In sum, the arguer is too arbitrary to determine the dimming of the sun is the major reason why the temperature on the earth dropped significantly without ruling out other possibilities

Secondly, even though the dimming of sun was indeed the major cause of the falling of temperature. The arguer provides no supports to sustain his point that such dimming must be led by the collision of a large meteorite or the eruption of volcanoes. Consider the possibility of the inter-stellar dusts blocking the sun. Or perhaps such dimming was the periodic phenomenon of solar activity, thus it is unrelated to the earth. In a nutshell, the arguer lends no evidence to support that the dimming of sun was linked with either the collision of meteorite or the eruption of volcanoes, therefore, making his/her deduction unreliable.

Finally, the arguer is too hasty in obviating the possibility of collision of meteorite with the earth as the cause of the appearance of cooling period. The mere surviving Asian records can hardly be convincing enough to espouse that there was a volcanic eruption in the mid-sixth century. The lacking of records of a flash caused by a collision is also not authoritative enough to ruling out such possibility. It is highly possible the record of the flash was lost considering that few records had survived. As a matter of fact, it is exceedingly difficult for one volcanic eruption to produce the large dust to block the sun globe-wide.

In conclusion, the argument is not persuasive as it stands. To make it more convincing, the arguer has to offer more information to support that the dimming of the sun was closely connected to the dropping of the temperature. Furthermore, s/he needs to prove such dimming was caused by the eruption of volcano exclusively.