[fig-tree]

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.


In this argument the author concludes that the global cooling in the mid-six century, based on some ancient historical records and a series of reasoning. However, I find this argument unpersuasive, as is discussed below.

The major problem with the reasoning lies in the exclusion of the possibility that a meteorite colliding with Earth caused the global cooling. This presumption cannot be well supported by the mere fact that no extant historical records of the time mention a sudden bright of flash of light. For one thing, since there are few historical records survive from that time, it is entirely possible that such a collision in fact happened and the flash of light created was recorded, but the records have already been lost. For another thing, it is also entirely possible that such a collision do happened, but the ancient people in Asia and Europe did not see it at all. Perhaps this collision happened in the opposite hemisphere of Earth, namely some regions of the South Hemisphere or the West Hemisphere. If either of the two is the case, then the possibility that collision caused the cooling cannot be confidently excluded, and the author's conclusion will be undermined to a large extent.

The argument is also based on a doubtable assumption that it was the dimming of the sun that caused the cooling. Common sense indicate that the dimming sun means less light arriving on the Earth surface, which will very possiblely lead to a cooling. However, since this cooling is presented as "extremely cold temperatures" by the author, it is questionable that whether this dimming is really significant enough to cause such an extreme cooling. If it is not, then the dimming is only one of the factors that contributed to this cooling, instead of the only cause or the major cause. Other factors might include climate changes and the decrease of carbon dioxide in the air. If this is the case, then all the reasoning following this assumption will be rendered meaningless.

Finally, the records about the boom are scant evidence that an overwhelming volcanic eruption happened. Perhaps this boom is created by other kinds of geological disaster such as a severe earth quake. Even if the records contain all necessary details about the sound, from which the author can conclude that the sound was surely created by a volcanic eruption, this evidence is still weak. Perhaps this eruption is not severe enough to create so much dust as to cause the cooling, and the loud boom recorded is due to the close distant between the volcano and the recorders.

To conclude, the provided evidences are too scant to support the author's line of reasoning and the conclusion. To bolster this conclusion more evidence should be provided that (1) No meteoric collided with the Earth in that time. (2) There was a direct relationship between the sun dimming and the cooling. (3) The loud sound is created by a volcanic eruption which was intense enough.

(i'm not a native speaker.)
Thank u very much!