Human response to climate change - The Global Climate System: Patterns, Processes, and Teleconnections - page 261

Minimum at the height of the LIA (see Section 8.3.2 ), there is a correlation
between harsher climates and low sunspot activity. The NAO (Section 2.2 ) most
likely reversed compared to the MWP, enhancing high pressure and outbreaks
of cold air from the north. The circumpolar vortex began to shift south as the
equatorial-polar temperature gradient increased. This lead to increased periods
of meridional circulation and blocking. Changes in circulation of deep bottom
water in the Atlantic may have had significant impacts on sea surface tempera-
ture levels and distribution, forcing a change in the circulation pattern over
Europe. There was also a considerable increase in volcanism across the globe,
especially from 1310 to 1317 and 1340 to 1350, compared to earlier centuries.
The resulting increase in particulate matter in the upper troposphere and lower
stratosphere would reduce incoming shortwave radiation to the Earth's surface
for several subsequent years. Brown ( 2001 ) emphasizes that teleconnections
with ENSO (Section 2.8 ) were absent.
The increased storminess resulted in periods of heavy sea flooding in northern
and western Europe. The flooding was enhanced by higher sea levels that existed
during the MWP. Enhanced erosion, exacerbated by clearing land and draining
marshy areas for agriculture, occurred. Flooding was especially prevalent up
until 1340, but then drier conditions under greater anticyclonic activity occurred
until about 1367.
Impacts on European society
Brown's ( 2001 ) detailed review establishes that worsening climate and weather
conditions created major agricultural production problems in Europe. Immediate
impacts occurred on the more marginal farming areas, at higher elevations for
example, that were at least partially viable during the MWP. Because peasants
tended to grow crops in strips, using open-field rotation, the risk of harvest
failure during wet or cold periods was enhanced. The variability of climate
meant harvests were erratic. For example, 1319 to 1322 were particularly bad
years. In 1322, grain production was only about 40% of the best years earlier.
1325 and 1326 also produced very poor harvests. Michaelowa ( 2001 ) lists the
relationship between prices of major agricultural products and weather varia-
tions. Wheat correlates negatively with summer and winter temperatures, but
positively with summer rainfall. Hay correlates negatively with precipitation,
and cattle production is reduced in lower autumn and winter temperatures. Rye,
barley, and oats seem to survive better the climate variations without significant
change to production. During the fourteenth century, most grain production in
Europe was wheat.
Because the feudal system did not encourage innovation and investment, and
life for the peasants meant severe poverty and day-to-day survival, a famine year
created an immediate impact. There were no food reserves, and diets were poor
anyway. Meat and fish were reserved for the rich. While the benefit of growing
legumes to enhance soil quality was known, this was not common practice.