Part 1. Past Climate Extremes and Impacts
As described in the Introduction, the Little Ice Age (~1450-1850 CE) was a significant period of cool climate in the Northern Hemisphere. The end of the Little Ice Age was especially cold, in part due to several volcanic eruptions (as you learned about in Lab 5), as well as reduced solar activity. In this section, we will explore major cold events in one of the coldest periods of the Little Ice Age (late 1700s to early 1800s), as well as their societal impacts. Below, take a close look at the NTREND temperature reconstruction during this period.
Figure 3: Northern hemisphere temperature anomalies around the end of the Little Ice Age (here, 1750-1830 CE) from Wilson et al (2016).
Stop and Think:
1.1 Identify the coldest individual year during the a) late 1700s and b) early 1800s shown in the figure. (Two years in total).
1.2 What caused or contributed to these two extreme cold years? Research this question online and summarize your findings on the activity sheet.
From the temperature reconstruction above, we are missing one important piece of information: how do temperatures vary over space (from one location to another) across the northern hemisphere? Fortunately, large networks of tree-ring and instrumental (or weather station) data can help us understand how climate has changed in both time AND space. The tree-ring datasets from the NTREND network, that were collectively analyzed to reconstruct large-scale temperatures (above), were also analyzed individually to investigate spatial patterns of climate (Anchukaitis et al., 2017, King et al., 2021). Using statistical techniques, information from each tree-ring site was used to develop a map of temperatures across the Northern Hemisphere for each year going back more than a thousand years.
For example, from Lab 5, you might recall the cold year of 1601 CE following the volcanic eruption of Huayanaputina in Peru (year 1600 CE). Take a look at the figure below adapted from King et al. (2021), which shows the spatial pattern of temperature across the Northern Hemisphere in 1601 CE based on the NTREND dataset. Here, the white symbols are tree-ring records used to produce the map of temperatures across space. The colors represent relative temperatures across space. Cooler colors show colder conditions, and warmer colors show warmer temperatures, which are shown as climate anomalieschanges in climate relative to a baseline (example, the average) in the map legend below).
Figure 4: Spatial characteristics of temperature across the northern hemisphere in 1601 (King et al., 2021).
Now let's take a look at the two extreme cold years during the Little Ice Age that you identified: 1783 and 1816. We will also zoom just into northwestern North America, where we will consider climate extremes in subsequent parts of this lab.
Figure 5: Spatial characteristics of temperature across the northwestern North America in 1783 (left) and 1816 (right). The colors are temperature anomalies, so cooler colors represent colder than average temperatures, and warmer colors are warmer than average temperatures. data from King et al. ( 2021).
Stop and Think:
1.3 What do you notice about the spatial patterns of temperature in both years across Canada and Alaska? Are they similar or different? How?
1.4 Based on the figure above, which event was colder in Alaska: 1783 or 1816? In an online search, can you find evidence of human impacts following this event specifically in Alaska? If so, what types of historical records provide this information?
1.5 Brainstorm why studying historical archiveshistorical documents or records (e.g., diaries, notes, official documents, etc) , in addition to paleoclimatea climate prevalent at a particular time in the geological past records, can be valuable for learning about regional climate extremes.
It is important to note that there can be significant regional differences in temperatures, even during events such as explosive volcanic eruptions that can cause large-scale cooling, sometimes lasting several years. Atmospheric circulation and other processes play a large role in how temperatures change across space after a volcanic event, thus influencing regional human impacts. While here we focused on cold extremes related to volcanism, changes in atmospheric and oceanic circulation (open this optional video from NASA in a different tab if you are interested in learning more), as well as human activities (see Part 2 of this lab) can also significantly impact regional climate. This is why a network of many tree-ring sites is so important for better understanding climate extremes in the past, and the climate processes that could cause extreme temperatures in the future.