On ice. (Letters).The article "Antarctic sediments muddy climate debate" (SN: 9/8/01, p. 150) says that evidence of past climate variations in Antarctica may invalidate in·val·i·date tr.v. in·val·i·dat·ed, in·val·i·dat·ing, in·val·i·dates To make invalid; nullify. in·val global warming global warming, the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. as a cause for the recent demise Death. A conveyance of property, usually of an interest in land. Originally meant a posthumous grant but has come to be applied commonly to a conveyance that is made for a definitive term, such as an estate for a term of years. of several ice shelves in that area. Isn't the length of time over which the changes occurred the critical thing? If the changes are occurring over roughly the same time span as they did in the past, then the recent changes can't be used to substantiate To establish the existence or truth of a particular fact through the use of competent evidence; to verify. For example, an Eyewitness might be called by a party to a lawsuit to substantiate that party's testimony. global warming. On the other hand, if the changes are taking place much more quickly, then they are significant and must be accounted for. Which of these two scenarios is true in this case? John Jaros Quakertown, Pa. The researchers weren't able to determine the precise rate of warming that led up to the ice-free period. Although greenhouse gases greenhouse gas n. Any of the atmospheric gases that contribute to the greenhouse effect. greenhouse gas emitted since the beginning of the Industrial Revolution could be significantly influencing the rate of recent ice-shelf demise, the scientists say that the fact that there was open ocean in portions of the Antarctic since the end of the last ice age suggests that those gases aren't the sole cause for melting ice. --S. Perkins |
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