Page 314 - Earth's Climate Past and Future

290 PART V • Historical and Future Climate Change

Little Ice Age Little Ice Age

As the last millennium began, scattered evidence from 25
Europe and high latitudes surrounding the North 15
Atlantic indicates a time of relatively warm climate Icelandic sea ice (weeks/year)
known as the medieval warm period. During this 5
interval (1000–1300), Nordic people settled southwest- 1000 1200 1400 1600 1800 2000
ern Greenland along the fringes of the ice sheet and Year
managed to grow wheat. Sea ice, common during the FIGURE 16-1 Sea ice on the coast of Iceland The frequency
past century around the Greenland coasts, is rarely of sea ice along the coast of Iceland increased into the nine-
mentioned in chronicles from this era. teenth century and then declined rapidly during the twentieth
The subsequent cooling into the Little Ice Age century. (Adapted from H. H. Lamb, Climate—Past, Present, and
(1400–1900) affected people in northern Europe. With Future, vol. 2 [London: Methuen, 1977].)
colder winters and a shorter growing season, grain
crops and grape harvests repeatedly failed in far north-
ern regions where they had been successfully grown Because major ice sheets did not actually form, the
during the medieval warm period, resulting in localized Little Ice Age was not a true ice age, but in some
famine. Lakes, rivers, and ports froze throughout regions it was at least a small step in that direction.
northern Europe during severe winters. Near the onset Much of the Canadian Arctic is a forbidding place with
of the Little Ice Age, the settlements in Greenland were long, cold winters and short, chilly, mosquito-infested
abandoned, in part because the marginal climate had summers. In a few locations, small ice caps that persist
become inhospitable but also perhaps because of con- at or near sea level are melting rapidly in the warmth of
flicts with native Arctic peoples. the modern climate. Rock outcrops in these regions are
The mountains of Europe hold dramatic evidence covered by lichen, a primitive, mosslike form of vegeta-
that climate was cooler than it is today. People who lived tion that can live on bare rock surfaces even under
in the Alps of Switzerland and Austria and the moun- inhospitable conditions (Figure 16–2A). These organ-
tains of Norway in the fourteenth and fifteenth centuries isms secrete acids that attack bedrock and break it down
experienced large-scale advances of glaciers firsthand. into mineral grains that provide nutrients. Small lichen
They wrote about the effects of these episodes on their growing in the Canadian Arctic today can be dated by
lives and sketched the advancing ice. Many of the ice their size (Figure 16–2B). They begin life as small
advances spread over alpine meadows where livestock specks and then expand into round blobs at predictable
had once grazed, and they destroyed farmhouses and rates.
even small villages where people had once lived. These Scattered across portions of Baffin Island northeast
historical expansions also prompted the glacial geologist of the Canadian mainland are broad halos of dead
Louis Agassiz to propose a theory that much larger ice lichen surrounding small, modern ice caps and also
ages had occurred tens of thousands of years earlier. occurring in high areas that now lack ice caps (Figure
Other evidence confirms that temperatures were 16–2C). These halos of dead lichen are a product of the
cooler in Europe and the nearby North Atlantic during Little Ice Age. The size of the lichen indicates that they
the Little Ice Age. One documentary record shows the must have developed over warm intervals of several
frequency of sea ice along the north and west coasts of hundred years in the relatively recent past and subse-
Iceland (Figure 16–1). Because fishing was vital to the quently been killed.
food supply on this isolated island, records were kept of Because lichen are tolerant of extreme cold, it is
times when coastal sea ice made it impossible for ships unlikely that frigid temperatures killed them. A more
to go to sea. This record shows the number of weeks likely explanation is burial beneath snowfields that
per year in which sea ice reached and blocked the blocked sunlight through the summer growing season.
northern coast of Iceland. If summer melting failed to remove the previous win-
Sea ice appears to have been infrequent until 1600, ter’s snow for many years in succession, the lichen
although records kept before that date may be less reli- would have died for lack of photosynthesis. The lichen
able than later ones. It increased in frequency and halos are an indication that growing snowfields covered
reached a maximum in the nineteenth century but then larger areas of high terrain on Baffin Island in the fairly
all but disappeared from the coasts during the twentieth recent past.
century except in occasional extreme years. This record When did the lichen die off? The small,young
indicates a major contrast near Iceland between the cold lichen now growing on top of the dead ones indicate
conditions of the Little Ice Age and the relative warmth that they have been present only during the last century
of the twentieth century. or so—since the end of the Little Ice Age. Expanded