Climatic variations over the millennia analyzed for predicting future climatic variability

Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest

by: Julie Loisel, Glen M. MacDonald, Marcus J. Thomson

Summarized by: Baron Hoffmeister

What data were used? This study used climate data from climate proxy databases and dendrochronology  along with computer software for modeling climate patterns  

Methods: This study used climate proxy data in conjunction with computer modeling and simulation software to determine hydroclimatic variability (i.e. the change in water conditions) in the North American Southwest.

Results: This study found that in the North American southwest is prone to variable climate conditions such as drought, as well as rapid snowmelt and severe rainstorms that can lead to flooding. Hydroclimatic variability in the southwest has not remained constant over the past one thousand years. In fact, there was high climate variability in the North American southwest during the Medieval Climate Anomaly (MCA; i.e. a period of warm climate that lasted from 950 c. to 1250) and the Little Ice Age (i.e. a period of cooling right after the MCA lasting until about 1850). Results show that the Little Ice Age had a higher amount of variability than the Medieval Climate Anomaly (see Figure 1). This was confirmed using climate data from tree ring growth analysis (i.e. the space between rings indicates the amount of growth) obtained by the North American Drought Atlas, a network of climate data points covering North America (figure 2), as well as climate proxy data from the El Junco diatom index from the Galapagos Islands. A diatom is a single-celled alga with cell walls made of silica. The oxygen used to make the silica is preserved in their shells and can be helpful climate proxy data.

Figure 1. This is a time series that displays annual climate variations based on the Palmer Drought Severity Index (i.e. climate data regarding precipitation and temperature). There is greater variability in the Little Ice age than the Medieval Climate Anomaly, and this can be seen by the bar graph at the bottom of the figure. This bar graph indicates the number of years where variability is above the 90th percentile.

This study also compared climate proxy records from fossil-coral oxygen isotopic records from Palmyra island in the tropical Pacific that recorded El Niño Southern oscillation patterns. El Niño Southern Oscillation is a weather pattern that has irregular periods of variation in wind and sea surface temperatures over the tropical eastern Pacific. Records of these weather patterns can be found in assemblages of certain coral fossils which serve as indicators for sea surface temperatures from the past. These were all analyzed and compared with the El Junco diatom index, and tree ring growth data using computer software. The researchers found a correlation between the El Niño Southern Oscillatory system and drought amplitude in the North American southwest increasing hydroclimatic variability. Also, with recent weather patterns, the computer simulations suggest that a ‘warm Little Ice Age’ scenario with high hydroclimatic variability accompanied by periods of warm and dry conditions is likely to occur sometime during the 21st century. 

Figure 2. The black border is the southwestern portion of North America being considered for this study. The black squares are climate data points provided by the North American Drought Atlas.

Why is this study important? This study shows how past climate change can help us understand how climate can change in the future and what the effects of that might be. In the North American southwest, hydroclimatic variability can lead to floods and drought impairing proper land management. Without experiments like this, climate change and its global effects cannot be understood. The results produced from this study can be used as a model for developing other climate reconstruction models.  

The big picture: This study explores the potential for climate variability modeling using historical climatic data as a reliable indicator for future climate predictions. It is important to be able to understand these historical climate events and weather patterns along with their effects on environments. Successfully being able to do this can lead to well-rounded land and water resource management in the face of climate change. 

Citation: Loisel, J., Macdonald, G. M., & Thomson, M. J. (2017). Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest. Plos One, 12(10). doi: 10.1371/journal.pone.0186282

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