"These charts, created by the Danish Meteorological Institute (DMI), provide observed and inferred sea ice extent for each summer month from 1893 to 1956. From 1893 to 1956, the Danish Meteorological Institute (DMI) created charts of observed and inferred sea ice extent for each summer month. These charts are based on compiled observations of ice conditions reported by a variable network of national organizations, shore-based observers, scientific expeditions, and ships as detailed in each report; in cases where no observations were available, the lead mapmakers extrapolated further ice cover using their knowledge of ice movement." (DMI - Danish Meteorological Institute).

The early surveillance of the Arctic Sea Ice has been of immense importance to the development of climate change science. It is the cause of the determination of global warming and the primary proof we have of the deterioration of sea ice, the heating of the oceans and the rice of Arctic temperatures. These seminal charts constitute one of the very most important sources to our understanding of this world-threatening phenomenon.

"Over the last three centuries, geographers, oceanographers, geophysicists, glaciologists, climatologists, and geoengineers have shown great interest in Arctic Ocean sea ice extent. Many of these experts envisaged an ice-free Arctic Ocean. This article studies three stages of that narrative: the belief in an ice-free Arctic Ocean, the potential for one, and the threat of one. Eighteenth and nineteenth century interest in accessing navigable polar sea routes energised the belief in an iceless polar sea; an early twentieth century North Hemispheric warm spell combined with mid-century cold war geostrategy to open the potential for drastic sea ice loss; and, most recently, climate models have illuminated the threat of a seasonally ice-free future, igniting widespread concerns about the impact this might have on Earth's natural and physical systems. This long narrative of an ice-free Arctic Ocean can help to explain modern-day scepticism of human-induced environmental change in the far north." (An ice-free Arctic Ocean: history, science, and skepticism).