There is a lot wrong with the catastrophic anthropogenis global warming hypothesis. On is that is is impossible to accurately recontruct the eath's average temperature over time. Recent claims that 1998 was the hottest year on record, for example, are highly questionable since the margin of error of the measurements is probably larger than the claimed increase in temperature. One issue that has troubled me is the reluctance of those making the claims to share their data, or to share the algorithms they used to massage the data, often by values much larger than their proclaimed temperature increases. Another issue is that the massaging of data results in falling temperaturess in the distant past and rising temperatures in the recent past. Here is an article by the Canadian Dr. Tin Ball that discusses these matters:

http://canadafreepress.com/index.php/article/3151