Detailed Chronology of Late
Holocene Climatic Change

James S. Aber

Table of Contents
Medieval optimum Medieval glaciation
Little ice age End of LIA
Grapes and wine References

The following detailed chronology of late Holocene climatic and historic events is based primarily on Le Roy Ladurie (1971), Grove (1988), Savage (1995), Nesje and Dahl (2000), and other sources as noted.

Medieval climatic optimum

Medieval glaciation

Little Ice Age

1816: Coldest single year on record in many places in Europe and North America, following the 1815 eruption of Mount Tambora in Indonesia. U.S. postage stamp depicts ice cutting in winter.

End of the Little Ice Age

Grapes and wine

Phenology is the study of seasonal dates of plant growth phenomena, such as flowering or ripening in fruit trees or grape vines. The date at which grapes ripen is mainly a function of summer temperature; warm, sunny weather results in an early wine harvest, and vice versa. Good historical records of the annual wine harvest have been compiled from towns in western Europe (France and Switzerland) by historians interested in the impact of climate on human activities (Le Roy Ladurie 1971).

The following chronology indicates a close correspondence between wine harvest dates and glacier advances during the Little Ice Age. Grape yield correlates most closely with mid-summer temperature. Early wine harvests generally coincided with glacier retreats; late harvests were times of glacier advances. However, glacier responses usually lagged 5-7 years behind the climatic changes indicated by wine harvest dates (Pfister 1981). Chronology of wine harvest dates and climatic conditions in western Europe is based on Le Roy Ladurie (1971).

During the late twentieth and early twenty-first centuries, global warming has impacted vineyards and wine production. When to harvest grapes for a fine wine is a delicate balance between three factors (Nicholas 2015):

  1. Acid content – gradually decreases to a low level as grapes mature and ripen.
  2. Sugar content – gradually increases to a high level as grapes mature and ripen.
  3. Flavor potential – reaches a peak at grape maturity then begins to decline.

Most of the potential flavor and quality of wine is created in the grape during the growing season and is already determined when the harvested grapes are delivered to a winery (Nicholas 2015). For optimal grape ripeness and wine flavor, all three factors achieve best balance in about three to four months depending mainly on summer temperature. Higher temperature speeds ripening and leads to grapes with higher sugar content. The process is highly sensitive for the thousands of varieties of Vitis vinifera grapes, each of which has unique conditions of soil and climate. For example, Pinot Noir and Riesling grapes prefer cool climate, whereas Cabernet is a warm-climate grape.

In spite of these differences, a global trend over the past few decades is increasing alcohol content in wine due to more sugar in grapes as a consequence of warmer summer temperatures in all major grape-growing regions (Nicholas 2015). A further consequence is that grape flavor components no longer reach their peak levels during the growing season in phase with optimum sugar and acid contents. This has significant implications for eventual wine flavor and, thus, value of the grapes and price of the wine.

The eventual result of this trend is possible relocation of vineyards into cooler climates at higher altitudes or latitudes. For example, southern Australian vineyards are moving into Tasmania. Oregon and Washington may gain new vineyards at the expense of California. Likewise in Europe, wine production may gradually shift from traditional regions in Spain, Italy, and southern France to southern England as well as northern France, Belgium, Germany and Poland. However, these changes are not likely to take place quickly, as developing a vineyard and producing high-quality wine takes many decades to perfect the grapes and production techniques.

Röbller Vineyard located on a hill top with 18 acres of grapes in the Missouri wine district. Several French-hybrid varieties are grown as well as the Norton, an American grape derived from Vitis aestivalis. This vineyard was established in 1988 and, thus, is still young. Kite aerial photo © SWA & JSA; see Röbller Vineyard.

The modern trends in vineyards and wines suggest that global warming in the twenty-first century is approaching or perhaps has equaled that of the Medieval climatic optimum a millennium ago, when vineyards existed 500 km north of twentieth century limits in northern Europe (see
last millennium).

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