Climate Through the Last Millennium

Calspace Courses

Climate Change · Part One
Climate Change · Part Two

      Climate Change 2 Syllabus

    1.0 - The Ice Ages: An Introduction
    2.0 - Discovery of the Ice Ages
    3.0 - Ice Age Climate Cycles

  4.0 Climate: Last 1000 Years
         · 4.1 - The Last Millennium
         · 4.2 - Tale of Viking Exploration
         · 4.3 - The Riddle of the Little Ice Age

    5.0 - Determining Past Climates
    6.0 - Causes of Millennial-Scale Change
    7.0 - Climate and CO₂ in the Atmosphere
    8.0 - Recent Global Warming
    9.0 - Climate Change in the Political Realm
    10.0 - The Link to the Ozone Problem
    11.0 - Future Energy Use
    12.0 - Outlook for the Future

Introduction to Astronomy
Life in the Universe

Glossary: Climate Change
Glossary: Astronomy
Glossary: Life in Universe

The Riddle of the Little Ice Age

Graph showing the relative temperature change from the Medieval Warm Period to the Little Ice Age.

The Little Ice Age and recent climate change

History is not just a bountiful resource; it is also a source of confusion. For example, in assessing current global warming and the human role in it, we are faced with the fact that the middle of the 19th century was unusually cold. Thus, we might ask, couldn’t the recent warming just be an expected return to more “normal” conditions following this cold period as existed in the early Middle Ages, before the Little Ice Age? Clearly, this problem can only be attacked extracting the long-term variability of climate by looking at even longer records.

The "Little Ice Age”, lasting from about 1350 A.D. to about 1850 A.D., was characterized by advances of mountain glaciers in most parts of the world and occasional spells of unusually cold winters in North America, Europe, and Asia. We commonly see European paintings from the 18th century that depict ice-covered rivers and lakes that have not been frozen for a life-time! In northern Canada, permanent snowfields developed, as seen in the age distribution of lichens growing on rocks.

Retreat of the Rhone Glacier shown by comparing the drawing from 1750 (top) and a photo from 1950 (bottom), demonstrating the changes since the Little Ice Age.

Among the possible reasons given for the "Little Ice Age" are low solar activity and increased volcanism. How then are we going to tell which part of the recent warming is "natural" and which (if any) is due to human influence? The standard answer to this question is that the warming right after 1850 is mostly natural. The weather in the mid- and late 1830s was highly unusual and highly stressful, with severe winters and bad harvests (The great Irish famine falls into this period.) In the conventional view, the "Little Ice Age" is an anomaly (indeed it was the coldest period in the last several thousand years) and the warming after 1850 simply gets us back on track. This concept also supports the idea that warming in the last century has been a good thing for people, plants and animals, because it brought back the previous regime of a more benign climate.

It is difficult to argue with this conventional view, but we must be aware that it is simply a convenient assumption: no more, no less. There is nothing in our understanding of climate that would forbid a continuation or worsening of the "Little Ice Age" conditions after 1850 and right into the present. On the contrary, the long-term view of climate change — the one that includes the coming and going of ice ages — actually demands increased cooling for the last 3000 years or so. That the Earth has come out of the "Little Ice Age" is much more in need of explanation than the fact that it got into one.