The animation of satellite data shows the physical extent of the ice cover for each of those minimum dates, ending with the record low. (scientificamerican.com)
Louis Agassiz identified the existence and extent of the ice sheets in Europe as early as 1837, but it wasn't generally accepted until the 1860s. (drtimball.com)
The yellow line shows the average extent of the ice pack (credit: NASA) (skepticalscience.com)