(graph from study being discussed)
For some time, climatologists have accepted the fact that from about the year AD 1000 to AD 1200, the temperature of the Northern Hemisphere was unusually warm. In fact, most studies indicate that it was warmer than it is today. This period of warm temperatures has been referred to as the “Medieval Warm Period,” the “Medieval Climate Anomaly,” or the “Medieval Climate Optimum.” A few hundred years later, the Northern Hemisphere experienced cooler-than-normal temperatures, and that part of earth’s history is sometimes called the “Little Ice Age.” Many climatologists argue that both the Medieval Warm Period and the Little Ice Age were limited to the Northern Hemisphere. However, a series of studies indicate that these periods of extreme temperatures were experienced worldwide.
I just recently became aware of these studies because the latest one appeared in my news feed. This study used the results of climate proxy data from 60 different sites. If you aren’t familiar with that term, it refers to data that scientists use to attempt to understand climate conditions of the past. Tree rings, for example, are sensitive to temperature and precipitation, so it is thought that we can use them to determine past climate conditions of the region where trees have been growing. Many climate-sensitive things like recorded harvests, coral growth, pollen grains, etc. can be used as climate proxies. The more climate proxies you have for a given region, the more likely you are to be able to determine the local climate conditions over the times for which you have those data.
As I said, the study used proxy data from 60 different sites to reconstruct the temperature of Antarctica over the past 1500 years. The overall graph from the study is given above. As you can see, according to the study, Antarctica was significantly warmer from AD 500 until AD 1250 than it is today. The pink region is the time over which the Northern Hemisphere experienced the Medieval Warm Period, and as you can see, the study’s data indicate that Antarctica was experiencing warmer-than-average temperatures as well. You can also see that those temperatures then fell over the next 750 years or so, producing colder-than-average temperatures. Thus, Antarctica seems to have experienced both the Medieval Warm Period and the Little Ice Age.
Interestingly enough, while the study’s data indicate that the whole of Antarctica experienced both the Medieval Warm Period and the Little Ice age, there were parts that did not. The Ross Ice Shelf region of Antarctica, for example, cooled during the Medieval Warm Period. The Weddell Sea and the Filchner-Ronne Ice Shelf also experienced some cooling during that period. Overall, however, the warming strongly outweighed the cooling, so Antarctica as a whole was warmer during the Medieval Warm Period than it is today. Also, looking at the part of the graph that deals with modern times, it seems that any warming that has occurred recently is simply a “recovery” from the Little Ice Age.
This same group has done similar studies that show that Oceania (the region of the earth that holds Australia, New Zealand, etc.), South America, and Africa/Arabia all experienced the Medieval Warm Period as well. Thus, the authors of these studies say that the Medieval Warm Period was not restricted to the Northern Hemisphere. Instead, it was experienced worldwide. In other words, worldwide temperatures were warmer in AD 1000-1200 than they are today.
While the data seem convincing, I will add one caveat. It is hard enough to measure global temperature today. If we measure global temperature using thermometers scattered across the world, the results look like this. If we use satellites, we get results that are quite different. So we don’t really know what global temperatures are today. Obviously, then, figuring out what global temperatures were from AD 1000 to AD 1200 is fraught with peril. Thus, while the studies’ conclusions are the best we have right now, they are far from certain.
Nevertheless, based on the best data we have, we can say that world was probably warmer before people began burning fossil fuels that it is today.
Thank you much for the paper! It’s confirms what I was taught. The Anasazi confederacy in the Southwest and Mexico ended thanks to the warming, which caused a drought. Some of the architecture is wonderful to see. Little of it is in ruins, thanks to the dry climate here. Oddly, the drought coincide with a group of ‘witches’ who may have been the Aztec. the people were said to be evil, practicing war only for love of war, and worshipped a dead witch as a god. After they were driven south, the drought began to end, but the cities were abandoned. The confederacy broke down into local groups whose children are with us today, the Zuni, Hopi, tohono groups. Pernicious anemia was a major factor in abandoning the cities. While the forests died, the mountains still gathered some rain, enough to grow small fields and feed for animals. Archeologists puzzled for a century about what happened to the confederacy. Then Rich Fisher asked Zuni friends. Apparently, no one bothered to, before 🙂 niio
During he Middle Ages, England hada wine industry, During the Maunder Minimum, the world had a mini ice Age. England doesn’t have a wine industry, anymore.