Sarah Palin is the only major candidate who has expressed doubts about manmade global warming - and she is right. This attack in the CS Monitor does not understand the interpretation of a temperature trend.
The common way to define a temperature trend is to equate it to the slope of a straight line that provides the ‘best fit’ for values of temperatures (usually yearly averages) plotted against time. The implicit assumption is that the trend does not vary with time.
But we know that’s not true; climate is always changing - warming or cooling. The ‘trend’ therefore depends on the choice of the time interval - the beginning year and the ending year. (Think of the fluctuations of the stock market.) And the choice is often quite arbitrary. So, for example, we have seen an overall warming trend since 1850, the end of the Little Ice Age [Akasofu 2008], and a cooling since 1998.
A different problem has to do with the quality of the data. It is generally agreed that atmospheric temperature data are more reliable than surface data.
But ‘global’ data from weather balloons go back only 50 years - and the truly global data from satellites only 30 years. The latter show a warming trend from 1979 to present. But one can also interpret the data as showing essentially zero trend from 1979 to 1997, followed by a sudden �jump� and another zero or even cooling trend since 1998 [NIPCC 2008, Fig. 13]. The point is that the observations do not correspond to what greenhouse models would predict.
So Sarah Palin is right. The temperature record shows a mixture of natural and human causes, with the latter quite a bit smaller. There is absolutely no reason to believe that anthropogenic global warming (AGW) will be of any consequence - even by 2100. And, of course, impacts of any AGW will be unimportant too.