Climate Change Human impacts

Tracking the transience of lake ice in a changing climate

Article: Lopez, L.S., B.A. Hewitt, and S. Sharma (2019). Reaching a breaking point: How is climate change influencing the timing of ice break-up across the northern hemisphere? Limn. Oceanogr. 9999, 1-11.

For centuries, people have been tracking seasonal lake ice patterns for a variety of reasons. To many communities, lake ice signals opportunity – it enables ice fishing, winter recreation, even access to remote locations. Take transportation in northern Canada, for instance: the Tlicho Winter Road provides an ice bridge atop which supplies can be hauled to remote indigenous communities of the Northwest Territories. It is the only ground route and is open for just a few months of the year while the lake ice is present. But these communities now face a serious threat: as climate change shortens the duration of the ice season, there is less opportunity to  receive sufficient supplies to last through the year.

Figure 1: Omiwatari (ice ridge) at Lake Suwa. (image credit: Zekkei Japan)

Because seasonal lake ice patterns are important to so many communities, especially those indigenous to these regions, ice records have been collected for centuries. Records even date back to Shinto priests who lived by Lake Suwa in Japan around the 15th century, who believed that large cracks in the ice were created by their god (see Figure 1). Today, this information can be used to tell us how climate change has altered the conditions necessary for ice on such lakes to exist.

Abrupt changes in lake ice linked to warmer spring temperatures

A recent study surveyed seasonal changes of lake ice freeze-up and break-up associated with the difference in air temperature, precipitation, and climate oscillations (such as El Niño) by examining lake ice records for 152 lakes in the Northern Hemisphere from 1951 to 2014. Using records from the Global Lake and River Ice Phenology Database at the National Snow and Ice Data Center, Dr. Lianna S. Lopez and co-authors from York University found trends suggesting broad changes to seasonal lake ice patterns across the Northern Hemisphere.

Using statistical analysis, Lopez found that 97% of lakes in the study exhibited ice break-up earlier in the spring season, averaging about one day earlier per decade between 1951 and 2014.

The trend varied between lakes of different location and depth, but the primary driver for earlier ice break-up was spring air temperature: warmer temperatures, earlier ice break-up. However, abrupt changes in spring ice break-up were often explained by sudden climate shifts, such as phase transitions of climate oscillations – cyclical changes to regional or global climates that cause fluctuations in temperatures, precipitation, and weather patterns of different regions on interannual to multi-decadal timescales. Some  examples include El Niño (ENSO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO).

Figure 2: A projection of lakes in the Northern Hemisphere that may experience intermittent winter ice cover in a warming climate. (Reprinted by permission from Nature Climate Change: Sharma et al. 2019)

For example, 1998 and 1999 were the most common years for early ice break-up among all of the lakes – two years following ENSO and PDO switching to their negative phases, associated with warmer weather in the Great Lakes. Similarly, a NAO phase switch in the 1980s, associated with warmer air temperatures in northern Europe, likely brought on the abrupt early ice break-up in Sweden and Finland during that time. In addition to climate oscillations, the lake altitude and depth determined the vulnerability of certain lakes to early ice break-up – low-lying, deep lakes were most susceptible to changes, while high-altitude, shallow lakes were less so.

A new normal

The study by Lopez was one of the first to identify the trends, drivers, and abrupt shifts in lake ice break-up in the Northern Hemisphere. Using over 60 years of data, the researchers were able to link changes in seasonal lake ice patterns – a vital component of local ecosystems, cultures, and economies – to warming temperatures and climate patterns over many decades.

While some lakes saw only modest changes, the impending pervasiveness of warming is undeniable: we are headed towards a new normal in which intermittent lake ice, and thus unstable living conditions for the wildlife and people in these regions, will become unavoidable (see Figure 2). The window of opportunity is closing for communities around the world that depend on lake ice; with adjustments already being made for voyages along the Tlicho Winter Road, the people of the Northwest Territories are some of the first who are threatened by disappearing lake ice caused by climate change.

Additional references:

Sharma, S., K. Blagrave, J.J. Magnuson, C.M. O’Reilly, S. Oliver, R.D. Batt, M.R. Magee, D. Straile, G.A. Weyhenmeyer, L. Winslow, R.I. Woolly (2019) Widespread loss of lake ice around the Northern Hemisphere in a warming world. Nature Climate Change, 9, 227-231.

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