| Summary: | Humanity has always lived under the threat of disasters such as famine. Now that these threats have diminished considerably in the West, it seems like people need a new scare that can be shared, thereby having a uniting effect. The possible impact of an increased atmospheric greenhouse gas concentration seems to have taken over this role. However, new dating techniques and numerous new studies have now added information that can bring about a reevaluation of the opinion that it is only human activity that can explain recent climatic changes. A distinction between trends and variability in climate is only possible if long-term records can be studied. Greenland ice core data yield well-dated information about climate over an extended period that, seen together with other data series, indicates that large, probably global scale changes have occurred at numerous times in the past. The warming during the past 100 y is not likely to be unique.
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