Climate change has been a hot topic for years. Climate change researchers often look at the ocean for clues to determine at what rate our global climate is heating up. Oceans are important indicators; whether you are looking at ice cover, water temperatures and circulation, or carbon dioxide absorption and release. Locally, we often look at the status of the Great Lakes for evidence of climate change, through changes in ice cover and water levels especially. Just how indicative of climate change are these factors?
CO2 Sink or Source
Human-caused carbon emissions are the number one contributing factor in global warming. Thankfully, the effects of these carbon emissions are offset by “sinks” on Earth. The ocean is especially capable when it comes to absorbing emissions and heat. Circulating currents within the ocean pull in CO2 and bring it into the depths of the oceans where it is stored in sediments and phytoplankton. As the ocean heats up, it will have a reduced capacity for absorbing CO2 and atmospheric heat.
Human Carbon Emissions are the number one contributing factor causing global warming. Credit: Text provided by Bloomberg Business. Data provided by NASA GISS and IPCC.
Lake Superior has been known to act as both a sink and a source of CO2. Studies from 1998-2000 suggested that Lake Superior was a net source of CO2. Dr. Soren Brothers and Dr. Paul Sibley recently published their analysis of surface oxygen saturation data collected from Lake Superior between 1968 and 2016. They found that Lake Superior absorbs CO2 from late May to early October but releases CO2 in the Winter. Soren and Brothers believe that a reserve of dissolved CO2 was released due to increased sunlight caused by effects of the 1997-98 El Niño but that Lake Superior is more typically a net sink for CO2.
Ice cover on the Great Lakes, particularly Lake Superior, is of great interest to many. The Ice cover dictates how we use the lake as a mode of transportation and recreation, and it changes the accessibility of remote habitats for wildlife. We also see it as a physical representation of climate change.
Ice cover percentages do not necessarily mirror short-term climate trends. For example this year, a small amount of ice remained on Lake Superior into May while the global climate continues to warm. NOAA–Great Lakes Environmental Research Laboratory (GLERL) has been monitoring ice cover on the great lakes for more than 30 years and continues to collect and study their data to better understand the long term effects of climate change on Great Lakes ice cover. For more information on the ice cover work by NOAA-GLERL Click Here.
One of the most often touted effects of climate change is an increase in water levels. Although this is fairly certain for the Oceans, the great lakes water levels are more difficult to predict. This is because precipitation is a huge contributing factor to lake water levels but, as anyone who lives around Lake Superior knows, weather is notoriously difficult to predict.
Climate change is predicted to cause an increase in major storms, which could increase precipitation over the Great Lakes, leading to higher water levels; however, we also anticipate more droughts in the years to come, which would increase evaporation. Currently water levels on the Great Lakes are fairly high. Researchers are still trying to develop more accurate models for predicting long term water levels in large lakes like Lake Superior.
An Indirect Measure for Climate Change
The reality is that all of these factors are interconnected and controlled by a variety of ever changing variables. Increased global temperatures can result in any number of changes to lake ecosystems. It may not be possible to accurately predict how climate change will effect the Great Lakes, but the potential for negative reactions is large. For now, we can continue to learn from our lakes and rivers and do our best to reduce the carbon footprint.