Medieval Warm Period

The Medieval Warm Period was a time when the climate was warmer in parts of the world, especially around the North Atlantic region. It happened from about 950 CE to about 1250 CE. During this time, temperatures were higher than before and after in some places, but it wasn't the same everywhere—it depended on the region.

Scientists study clues from nature, called climate proxy records, to learn about how warm it was back then. These clues show that the warmest times were different for different areas, so the Medieval Warm Period wasn't exactly the same all over the world.

After this warm period, some areas became cooler, leading to a time known as the Little Ice Age. People think several things might have caused the Medieval Warm Period, like changes in the sun's activity, less volcanic eruptions, and shifts in ocean currents. These natural changes, along with some outside forces, likely played a role in making the climate warmer during this time.

Research

The Medieval Warm Period was a time of warmer weather in parts of the world from about 950 CE to about 1250 CE, during the European Middle Ages. Some scientists split this period into two smaller parts: one from around 450 CE to 900 CE, and another from about 1000 CE to 1300 CE.

In 1965, a scientist named Hubert Lamb studied information from plants, old documents, and weather records. He found that the world was warmer around the years 1000–1200 CE, followed by a colder time called the Little Ice Age. Later studies showed that this warm period was not the same everywhere in the world. Some places were warmer, while others were not as warm as thought before. Scientists still use the names "Medieval Warm Period" and "Little Ice Age" to describe temperature changes in history.

Global climate during the Medieval Warm Period

There has been much debate about whether the Medieval Warm Period was a global event or just a regional one. In 2019, researchers using extended data confirmed that this warm period was not the same worldwide. The warmest 51 years during this time happened at different moments in different places. Scientists now suggest thinking of it as a regional change rather than a global one. Research also shows that global temperatures were quite stable for thousands of years before the industrial revolution, without a single global warm period or a cold period called the Little Ice Age.

Main article: climate variability

Main articles: Common Era

North Atlantic

Lloyd D. Keigwin's study from 1996 looked at data from the Sargasso Sea and found that its sea surface temperature was cooler around 400 years ago and also cooler 1700 years ago. However, it was warmer about 1000 years ago during a time called the Medieval Warm Period.

Studies using sediment samples from Puerto Rico, the Gulf Coast, and the Atlantic Coast from Florida to New England found evidence that there were more tropical cyclones in the North Atlantic during the Medieval Warm Period. This was followed by a time with fewer cyclones.

Iceland

Iceland was settled between about 865 and 930, during a warm time good for sailing and farming. Studies of marine cores and mollusc growth patterns from Iceland show that summer temperatures stayed warm after the first settlers arrived, but winter temperatures got colder.

Greenland

Studies found that parts of southern Greenland and North America were warmer from 950 to 1250 than they were from 1961 to 1990. However, a study from Columbia University suggests that the warm weather in Greenland lasted only a short time. Around 1000 CE, the climate was warm enough for Vikings to travel to Newfoundland and set up a small settlement there.

Around 985, Vikings started settlements in Greenland called the Eastern and Western Settlements. At first, they raised cattle, sheep, and goats, and got about a quarter of their food from the sea. But after the climate became colder and stormier around 1250, they relied more on sealing for food. By around 1300, seals provided most of their food.

By 1350, there was less demand for their goods, and trade with Europe dropped. The last record from the settlements is from 1412. Over the next few decades, the remaining people left, mostly because farms were becoming more available in Scandinavian countries.

Europe

Winters in Central Europe were mostly cold between 1000 AD and the late 1890s. However, there was a long stretch of warm summers from about 1170 to 1310, with a very cold period between 1195 and 1197. Many smaller glaciers in southern Europe melted during this time, while larger ones survived and give us clues about the past climate.

In addition to warming from melting glaciers, eastern Europe saw more flooding during this period, likely because of more rain linked to changes in the North Atlantic Oscillation. Climate change also changed landscapes. For example, a coastal area in western Sardinia that the Romans had left became more open land during the Medieval Warm Period, allowing it to grow without people living there. When people returned, they found a changed landscape and had to rebuild ports. In the Iberian Central Range, lakes were more productive, soil eroded more, and there were frequent heavy rains.

Main article: Tropical cyclones and climate change

Other regions

North America

In places like Chesapeake Bay in Maryland and Virginia, scientists noticed big changes in temperature between about 950 to 1250 CE and again during a cooler time called the Little Ice Age. Some areas, like the Hudson Valley, were drier during this warm period. In Connecticut, salty water went farther inland because of higher sea levels.

Many parts of western North America, like California and the Great Basin, had long dry spells. Alaska had warm times in three different periods. Studying this warm time helps us understand when people lived in places that are now very dry.

Africa

Eastern Africa switched between wetter and drier times. During the warm period, it was drier. Near the Canary Islands, bones showed that the air got colder by about 5°C, but the people there kept eating much the same foods.

Antarctica

The warm time in the Southern Ocean started later than in the North Atlantic, about 150 years later. Some parts of Antarctica were colder, while others were warmer between 1000 and 1200.

Pacific Ocean

Coral in the tropical Pacific Ocean shows that the water was cooler and drier at the start of this warm time. A study found that the Pacific was warmer during this time than in later cooler periods, but not everywhere was the same.

South America

In Chile and Ecuador, scientists found signs of this warm time in lake sediments and ice. In tropical South America, the warm time lasted from about 1050 to 1300, followed by cooler weather in the 1400s.

East Asia

In China, scientists looked at temperatures over 2000 years and found that some parts got warmer from the 10th to the 14th centuries, similar to today. The weather changed a lot in different places. In far eastern Russia, some areas had lots of floods while nearby islands had less rain. In Japan, there was a warm and wet time from 900 to 1200.

South Asia

In India, there was more rain during this warm time because of changes in ocean patterns. Evidence from lakes and plants in places like Himachal Pradesh and Kerala shows it was warmer and wetter.

Middle East

In the Arabian Sea, the water got warmer and had more life. The Arabian Peninsula was even drier during this warm time, with long dry spells until about 660 years ago.

Oceania

There isn’t much data from Australia about this warm time, but some clues from lakes suggest it might have been wetter in some places. In New Zealand, studies of caves and tree rings show that this warm time happened between about 1050 and 1400 and was warmer than today.