Earth's Heat Budget: How Lakes and Glaciers Are Connected

Kellie Schaefer,

Michigan Technological University

When I initially signed up for JIRP, I had no idea how I would be able to find a connection between my field of study and glaciers. The only correlation between the two that I could think of was the fact that about 2 billion people worldwide rely on annual snow pack and glaciers for drinking water (Griggs, 2015). On that note, it is relevant to mention the fact that approximately 90% of the city of Anchorage, AK relies on the Eklutna Glacier for drinking water, and about 15% of its electricity comes from a hydropower plant that utilizes meltwater from the glacier (Sinnott, 2013). While this idea was fascinating to me, I wanted to find other connections between Environmental Engineering and glaciers.

Now that I am back in school, I am finding that what I learned on the icefield can be found everywhere in the classes that I am currently taking. My Senior Design project involves calculating a mass balance model to find various concentrations of copper in a mining basin. Soil Science has showed me just how important glaciers are when forming landscapes and depositing till in certain areas (not to mention the fact that we get to dig pits, although digging a dirt pit is a much slower process than digging a snow pit). In Geohydrology, we discussed how the global groundwater flux, or movement of groundwater over a specific area, is almost equivalent to global glacial meltwater flux. Surface Water Engineering brought up the fact that inland freshwater lakes are being affected by a change in Earth’s climate due to an imbalance in our heat budget.

 Meltwater from the Thomas and Lemon Creek glaciers pours into small lakes (green with glacier silt), and continue on to Lemon Creek and the Pacific Ocean. Photo by M. Beedle.

Meltwater from the Thomas and Lemon Creek glaciers pours into small lakes (green with glacier silt), and continue on to Lemon Creek and the Pacific Ocean. Photo by M. Beedle.

This “heat budget” concept really struck a chord with me. The sun emits shortwave radiation, which enters our atmosphere. This shortwave radiation can be reflected back into space (clouds), absorbed by Earth’s surface, or absorbed by chemical compounds in the atmosphere and re-emitted as longwave radiation back to Earth’s surface. Typically, the Earth would have a balanced heat budget, with incoming radiation equivalent to outgoing radiation. The atmospheric chemistry of the Earth has been anthropogenically altered, and now the heat budget of the Earth is imbalanced. Greenhouse gases absorb reflected shortwave radiation from the Earth’s surface, and re-emit it as longwave radiation. 

What does this imbalance in Earth’s heat budget mean? In terms of surface water, lakes are absorbing more shortwave radiation and increasing in temperature. This is especially true for Lake Superior, which has had an increase in mean lake temperature by 2.5°C since 1976. Additionally, winter ice cover has been reduced by 23% - 12% over the last 100 years (Austin and Colman, 2007). This decrease in the ice cover results in a lower albedo for the lake. More shortwave radiation is absorbed during the winter months, increasing the temperature of the lake. This positive feedback has gradually resulted in reduced ice cover and increased lake temperatures. Freshwater fish require specific temperatures in order to survive, and this increase in lake temperature results in a reduction in the ideal environment for some fish species. Similarly, glaciers provide specific temperatures required for salmon spawning. Streams fed by glacier meltwater become cooler, allowing salmon to spawn in streams that would otherwise be too warm. The decreasing mass in glaciers can sometimes lead to a reduction in the glaciers surface area. This results in a lower albedo for that particular area, since the glacier is no longer reflecting the incoming solar radiation. 

On a global scale, the reduction in glacier surface cover and the shortened ice cover period of inland lakes is resulting in an overall lower albedo. The Earth’s heat budget continues to become more and more imbalanced, with more heat being retained in Earth’s atmosphere than is being emitted back into space. Positive feedback cases such as a reduction in ice cover, both with glaciers and lakes, is resulting in more retained heat. We cannot afford to allow Earth to reach a point where it is impossible to return to a balanced heat budget.

References

Austin, J. A., and S. M. Colman (2007), Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback, Geophys. Res. Lett., 34, L06604, doi:10.1029/2006GL029021.

Griggs, M. B.. (2015), Two Billion People Rely On Snow For Drinking Water, And Supplies Are Melting." Popular Science. Environmental Research Letters, 12 Nov. 2015. Web. 27 Sept. 2016.

Sinnott, Rick (2013), As Eklutna Glacier Shrinks, Anchorage's Water and Power Will Become More Expensive. Alaska Dispatch News. N.p., 15 Dec. 2013. Web. 27 Sept. 2016.