Prior to 1979, there is very little evidence as to the actual effects of incomplete observational coverage, or of blending air and SST measurement, on estimated trends in global temperature. (climateaudit.org)
That said, what do you think the value of estimating trends might be? (climateaudit.org)
Perhaps the simplest case is linear regression of a single variable — we use it, for instance, to estimate the trend rate over time, as for instance of global temperature. (tamino.wordpress.com)