If glacier data is a little incorrect but helps that effort, then the data is true in all but a very narrow and clinical scientific sense. (realclimate.org)
(George Monbiot's article in The Guardian documents a similar case of systematic misrepresentation of glacier data by skeptics.) (realclimate.org)
In a previous post entitled Worldwide Glacier Retreat, we highlighted the results of a study by J. Oerlemans, who compiled glacier data from around the world and used them to estimate temperature change over the last ~ 400 years. (realclimate.org)