What was done
On the Danish island of Anholt in the middle of Kattegat (a shallow marine sea bounded by the west coast of Sweden and the east coast of Jutland that is connected to the North Atlantic Ocean), the authors studied sedimentological and geomorphological properties of the island's dune system, employing optically-stimulated luminescence dating and aerial photography, which work they conducted at various times between April 2002 and September 2005.

What was learned
Clemmensen et al. say their data indicate that "the last aeolian activity phase on Anholt (AD 1640-1900) is synchronous with the last part of the Little Ice Age," noting that "dune stabilization on Anholt seems to a large degree to have been natural, and probably records a decrease in storminess at the end of the 19th century and the beginning of the 20th century." In addition they report that this timing "is roughly simultaneous with dunefield stabilization on the west coast of Jutland and on Skagen Odde, citing the work of Clemmensen and Murray (2006).

What it means
Stating that, today, the dunes of Anholt "are largely inactive," the Danish researchers write that "the evidence of widespread dune formation on Anholt is indicative of increased storminess in the Kattegat region," noting further that "the period of sand drift and dune formation took place during the latter part of the Little Ice Age, which is characterized by increased (summer) storminess in large parts of NW Europe." Hence, it is clear that the global warming of the 20th century was accompanied by a dramatic reduction in the storminess of a significant portion of northwest Europe.

Reference
Clemmensen, L.B. and Murray, A. 2006. The termination of the last major phase of aeolian sand movement, coastal dunefields, Denmark. Earth Surface Processes and Landforms 31: 795-808.