Climate in the Recent Past

Climate is never perfectly stable — it keeps varying, and the recent past gives us plenty of evidence. The twentieth century alone saw dramatic swings: extreme weather, record warmth, and devastating floods and droughts. These events are not random curiosities; they are part of a longer pattern of climate variability that we can trace through historical records.

The 1990s stand out as the warmest decade of the twentieth century, and it also brought some of the worst floods recorded around the world. But the century's climate extremes were not confined to that decade. From 1967 to 1977, the Sahel region — the belt of land just south of the Sahara Desert — suffered a devastating drought that lasted a full decade. Earlier, during the 1930s, severe drought struck the southwestern Great Plains of the United States, an episode so destructive it became known as the Dust Bowl.

How do we know about these changes? Historical records of crop yields and crop failures, accounts of floods, and records of human migration all tell us how changing climate affected people's lives. When harvests failed or lands became uninhabitable, people moved — and those movements are themselves evidence of climate shifts.

Europe's history offers a particularly clear picture of alternating climate phases. The continent repeatedly experienced warm, wet, cold, and dry periods. Two episodes stand out as especially significant:

• Warm and dry conditions in the tenth and eleventh centuries — this was the period when the Vikings settled in Greenland, possible only because the climate was mild enough to support their settlements.
• The "Little Ice Age" from 1550 to about 1850 — a prolonged cooler phase that affected Europe for roughly three centuries. …