ARGUMENT45 - The following appeared as an editorial in a wildlife journal.
"Arctic deer live on islands in Canada's arctic region. They search for food by moving over ice from island to island during the course of a year. Their habitat is limited to areas warm enough to sustain the plants on which they feed, and cold enough, at least some of the year, for the ice to cover the sea separating the islands, allowing the deer to travel over it. Unfortunately, according to reports from local hunters, the deer populations are declining. Since these reports coincide with recent global warming trends that have caused the sea ice to melt, we can conclude that the decline in arctic deer populations is the result of deer being unable to follow their age-old migration patterns across the frozen sea."
字数：451 用时：00:30:00 日期：2007-8-11 13:56:05
The speaker asserts that the decline in arctic deer populations is the result of deer being unable to follow their migration patterns. To support his assertion, he cites the fact that local hunters report that deer populations are declining. Also, he points out that recent global warming trends caused the sea ice to melt. Careful examination of these evidences, however, reveals that they render little credible support to the assertion.
To begin with, the arguer unfairly assumes that the local temperature condition reflects the trend of global warming. However, absent evidence there is, it is as likely that the local temperature condition is the same as that was in the past. Or even, perhaps local temperature actually is lower than ever because of certain geological reasons such as cold ocean currents nearby. In short, without elaborate materials provided, I am not convinced about the assumption that local temperature is rising.
Secondly, that local hunters reporting less deer is little indication that the population of arctic deer is declining. Since it is entirely possible that the hunters' assumption is based on the fact that they encounter less deer. And the reason why less encounters happen perhaps is that the activity ranges of hunters and that of arctic deer seldom overlap. Or, the fact that the deer are hidden themselves for sleep during the time of hunting also makes encounters less. In either event, naturally, the hunters would report that the population of deer is declining. In short, without ruling other possibilities, I find the assumption that there exist less deer unjustifiable.
Finally, even if the local area is warmer than the past, and even if the amount of arctic deer is diminishing, we cannot blame the change of migration patters caused by melting ice for this tragedy. After all, the change of migration patters is not necessarily fatal for arctic deer and they can get over it. Besides, there are more other factors that might result in the death of deer. For example, local hunters excessively kill arctic deer for their meat. Or, perhaps the plants on which they feed are less and less because of the upheaval of climate. What is more, it is possible that arctic deer themselves are not capable to survive due to the evolutionism. Simply put, without further evidence presented, the arguer is too hasty to draw a conclusion that change of migration patters should be responsible for the decline of deer population.
In sum, the assertion is logically flawed and therefore unconvincing as it stands. To bolster the assertion, the arguer needs to provide more evidences as following:(1) a local temperature report confirming that the habitant of arctic deer is warmer than the past;(2) an arctic deer "demographic census" confirming that the population is actually declining;(3) a study showing the causal relationship between the change of migration patterns and the death of arctic deer.