With the lack of ice, why is there little evaporation?

The lack of ice on the Great Lakes is certainly an unsettling occurrence this 2016 winter. On March 8th, Great Lakes Ice Coverage was 8.6%, while it was at 73.7% in 2015, and 91% percent in 2014. 5*

Topsy-turvy weather and evaporation effects have led to low ice this year, and very high ice the prior two years.
While weather varies and changes from one day to the next, it seems to fluctuate to more extremes more often. For more perspective on ice coverage, we need to step further back. From 1973 to 2010, spatial extent of ice coverage decreased in the Great Lakes by about 71% - a climate trend of decreasing ice coverage - impacting Georgian Bay water levels without question.

The usual assumption around low ice cover would be that the Great Lakes would experience more evaporation since there is no 'lid' to keep the water in when the cold air drafts across the warmer than usual water.

However, this is not always the case - and not the case this winter. Understanding this connection in the Great Lakes is a new field of study since the scientific instrumentation has only recently been installed.

Evaporation this winter will be low.

The increased surface water temperature3 and warmer than average air temperatures actually results in minimal evaporation rates due to a lower thermodynamic energy difference.

This higher energy point may then set up for more significant evaporation later on this year or next - depending again on the weather.
Think of the lake as a large heat storage battery. This is why the Great Lakes can actually create their own microclimate. The hot summer sun warms the water throughout the warmer months. In the winter, when a cold arctic blast sweeps across the surface the cold air sucks heat out of the lake in the form of evaporating water. This is where lake effect snow comes from.

In the summer when both the air and the water are comparably warm (i.e. no thermodynamic energy difference)...we see little or no evaporation. It is actually only in the cooler winter months when the water is warmer than the air, that most of the evaporation from the Great Lakes occurs.

Evaporation effects on ice and vice versa:
2 general cases to consider

Case 1 - a warm/low ice winter like the El Nino of this winter

    1. Current season - When the water is 5 degrees and the air is 5 degrees there is again no thermodynamic force to drive the water into the air. So the water doesn’t evaporate.
    2. There isn’t much spring snow melt or lake ice melting, so the sun’s heat actually goes immediately into warming the water that continues to gain heat throughout the summer.
    3. Later - we can imagine in this case, that the fall water temperature will be hotter. Then, if the winter brings cold dry air from the arctic, there will be more thermodynamic energy driving the warm water into the cold, dry air before any state change and so, more evaporation occurs.

Case 2 - a cold/high ice winter

    1. The other important piece of this puzzle is “state change” or “phase transition”. Freezing liquid water to form solid ice requires energy to be removed from the water. This means that even without a change of temperature, energy moves from the water into the air. And once that is completed, the heat in the liquid water now covered by the ice is insulated from the air.
    2. Next, the spring melt and lake ice melting absorbs energy even without the temperature rising above zero. Then, once the phase transition is completed, the water temperature starts to increase.
    3. More phase change energy means less evaporation. This could lead to more ice in the subsequent season and higher water levels.

Jan water levels up..
Higher precipitation and low evaporation weather effects contributed to water levels actually rising in Lakes Huron and Michigan in January by about an 1". Typically, January is a month where water levels decline - the January average for the last 98 years has been a decline of about 1.5". December saw very high amounts of precipitation - 6" verses 1" normally.2

Over the long term, most climatologists predict long term declines of water levels - but periods of high water are possible with weather effects such as flashier storms.
Keeping watch - higher temperatures, water concerns and climate change
Weather and climate are influencing each other. The short term weather patterns are seeming to become more extreme, being driven by longer term climate patterns that are affected by human induced global warming. Continued extreme weather over a long period will effect the climate.

At Georgian Bay Forever, we continue to pursue understanding of the longer term impacts of human induced global warming on the climate of the Great Lakes. Climate change threatens the balance of water levels, water quality, and ecosystems in Georgian Bay that have kept it swimmable, drinkable, and fishable for generations.

To quote a famous scientist around learning and understanding,

" Principles for the Development of a Complete Mind: Study the science of art. Study the art of science. Develop your senses - especially learn how to see. Realize that everything connects to everything else."
Leonardo da Vinci

About Georgian Bay Forever:
Georgian Bay Forever is a charity that funds and supports scientific research and education that protects and enhances the waters of Georgian Bay, as part of the Great Lakes. Our vision is that Georgian Bay waters are healthy and thriving for future generations. Learn more about how you can support out work.

*This post was updated Feb 25 to change the first paragraph Great Lakes ice coverage numbers to Feb 24th numbers from GLERL (NOAA). See reference 5. It was then updated March 9th, with March 8th information

References used in this post:

1 Gaertner, Eric. "Great Lakes ice cover still significantly less than last 2 winters". www.mlive.com. Feb 16. Retrieved Feb.18 at https://www.mlive.com/news/muskegon/index.ssf/2016/02/great_lakes_ice_cover_still_si.html
2 Torregrossa, Mark. " Two Great Lakes Accomplish A Rare Winter Feat". www.mlive.com. Feb 18. Retrieved Feb.19 at https://www.mlive.com/weather/index.ssf/2016/02/two_great_lakes_accomplish_fea.html
3 Water in Lake Huron is +3.5°F higher (Mid - February 2016) than previous two years. National Oceanic and Atmospheric Administration.
4Leonardo da Vinci. Retrieved from: color="026cb6">https://www.goodreads.com/quotes/112565-principles-for-the-development-of-a-complete-mind-study-the target=
5 Post was updated with Feb 24 ice coverage numbers from GLERL (NOAA - Great Lakes Environmental Research Laboratory) GLCFS Annual Comparison. Retrieved on Feb 24 at https://www.glerl.noaa.gov/res/glcfs/compare_years/. It was then subsequently updated with March 8th numbers.

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