Biologist tracks climate change drivers from as far back as medieval era

York biology Professor Sapna Sharma is interested in predicting the effects of environmental stressors – for example, climate change, invasive species, land use change and habitat alteration − on ecosystems, and improving the scientific approaches used to generate these predictions. Some of her latest research, funded by the Natural Sciences and Engineering Research Council (NSERC) and others, and published in Scientific Reports, suggests that environmental stressors are driving the long-term changes in ice seasonality.

What’s remarkable about this study is that Sharma’s international team − including researchers from the Finnish Environmental Institute, the University of Wisconsin-Madison, Rutgers University, the Center for Integrated Data Analytics (Wisconsin) and Osaka Prefecture University (Japan) – had access to records of ice freezing and melting that had been collected, directly by human observation, centuries prior to the start of the Industrial Revolution. In fact, this research team turned to records as far back as medieval Japan and Finland on the eve of Enlightenment, and over a vast period of time, which extends to present day.

There’s a lot to be learned from ice. The dates of lake and river ice freezing and melting or breaking up can be used to analyze climate change because ice responds sensitively to climatic change and variability.

When did we start looking at ice in this way? Quantitative, direct annual observations by humans of climatic variables starting before the Industrial Revolution – that is, the 1840s – are rare. That’s why Sharma’s research has captured the imaginations of many. Scientists and non-scientists are intrigued by the notion of what this old ice data can tell us.

Study offers rare glimpse from centuries back

In this study, Sharma’s team analyzed climate-related changes of ice freeze dates from 1443 to 2014 for Lake Suwa, Japan; and of ice breakups from 1693 to 2013 for Torne River, Finland. Together, the two data groups, from two geographic locations very far from each other, tell a collective global story about climate change.

Who was documenting ice records in medieval Japan and pre-Enlightenment Finland, and why? Ice records were collected mainly for religious or economic purposes. Interestingly, the long-term ice freeze record for Lake Suwa, in Japan, was collected by Shinto priests observing a legend in which the male god Takeminakata would cross the lake to visit the female god Yasakatome at her shrine on the other side of the lake.

Since 1443, the long-term ice freeze record for Japan’s Lake Suwa was collected by Shinto priests.

In Finland, the record for the date of ice breakup for Torne River was started by a merchant named Olof Ahlbom in 1693. (There are only seven years missing data in this time when Olof had to flee Finland when the Russians invaded.) The ice breakup time series was preserved due to Torne’s important role in trade, transportation, food and recreation beginning in the 17th and 18th centuries.

Interestingly, ice breakup guessing competitions since the 20th Century reveal, to the minute, when the river ice melted as thousands of people bet on the timing of river ice breakup on Torne River.

With this data in hand, Sharma’s research team sought to answer the following questions:

• Do ice dates reveal more rapid warming?
• Do warm extremes increase in frequency?
• Do drivers (i.e. explanatory factors) of ice seasonality change?

Ice seasonality has been associated with local weather at seasonal scales, such as temperature and precipitation, and large-scale climatic drivers, including the solar sunspot cycle, North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO).

Ice breakup guessing competitions since the 20th Century reveal, to the minute, when the river ice melted as thousands of people bet on the timing of river ice breakup on Torne River in Finland.

Key findings tell story of warming trends and no freeze years

Sharma’s research found three main things:

1. A shift towards later ice formation for Suwa and earlier spring melt for Torne;
2. Increasing frequencies of years with warm extremes; and
3. Stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution.

Importantly, two things happened after the Industrial Revolution: The researchers found a significant relationship between 1) ice dates and atmospheric CO2 concentrations for Suwa and 2) ice dates and air temperatures for Torne. For air temperatures, the effect of warmer winters on delaying the Suwa ice date was significantly greater than the effect before the Industrial Revolution, and warmer springs were correlated with earlier ice breakup dates in Torne after the Industrial Revolution.

Important drivers after the Industrial Revolution

Sharma emphasizes that the most important explanatory factors for ice freeze and breakup dates were atmospheric carbon dioxide (CO2) concentrations and local seasonal air temperatures – March, for Suwa and January-April, for Torne.  In addition, NAO was significant for Torne after the Industrial Revolution, while for Suwa ENSO was not a significant predictor in either period.

“Although local factors influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems,” Sharma explains. “This suggests that global processes including climate change and variability are driving the long-term changes in ice seasonality,” she adds.

This research was funded by NSERC, the North Temperate Lakes Long-Term Ecological Research Program at the University of Wisconsin-Madison, U.S. National Science Foundation, U.S. Geological Survey Office of Water Information and Rutgers Institute of Marine and Coastal Sciences and the Cooperative Institute of the North Atlantic Region.

The article, “Direct observations of ice seasonality reveal changes in climate over the past 5-7 centuries,” was published in Scientific Reports (2016), which is published by Nature Publishing Group.  For more information, visit the Sharma Laboratory website.

By Megan Mueller, manager, research communications, Office of the Vice-President Research & Innovation, York University, muellerm@yorku.ca