Climate Change

Climate Change Impacts on Kahshe and Bass Lakes

What is climate change and what is driving it?

Since the Industrial Revolution, humans have altered the earth’s atmosphere by burning coal, oil, and gas to power our global economy, thereby releasing massive amounts of carbon dioxide (CO2) into the atmosphere. CO2, as well as methane, water vapor, and nitrous oxide (NO2), are the primary insulating gasses in our atmosphere and collectively are referred to as greenhouse gasses. While each plays a role in the warming of the atmosphere, CO2 is the most important at present, because our actions have and continue to rapidly increase its concentration in the global atmosphere.

Complex global climate models now enable climate scientists to project the likely climate in coming decades, based on a host of assumptions on how large the economy will become and how much of the energy used will be derived from coal, oil, and gas or wind, water and other forms of renewable energy. Using the output of 19 different global climate models, the Muskoka Watershed Council (MWC) was able to project future changes in temperature and precipitation patterns and their impacts on the terrestrial and aquatic environment for the period up to mid-century (2041 to 2070).

This overview page briefly discusses the present and possible future changes in the climate of Canada and Ontario and their potential impacts on Muskoka’s terrestrial and aquatic resources.  These potential impacts are described in reports released by the Muskoka Watershed Council (MWC, 2016), the United Nations Intergovernmental Panel on Climate Change (IPCC, 2018), and the Government of Canada (2019).

What are the potential impacts?

From the MWC’s modeling, a projected mid-century temperature increase for May through September appears to lie somewhere around 2.5oC, which is projected under a medium level of carbon emission reduction. The more recent 2019 Government of Canada document provides similar projections for average annual temperature increases in Ontario for three 20-year periods through to the end of the century. The values presented are for the 50th percentile of model runs with the bracketed values shown for the 25th and 75th percentiles. The temperature increases are based on comparisons to a reference period of 1986-2005.

To give some perspective on how these projected temperature increases compare to current-day temperatures, the figure below plots the average daily mean temperature for each month of the year over the past six years (2016-2021) against the 30-year normal and the MWC’s projected temperatures. We are currently well below the projected mid-century levels for the months from June through September, but that is not the case for the winter and early spring months where current temperatures are already at or near the projected levels.

Based on the MWC model projections, the  impacts of these projected temperature and precipitation changes may include:

• Flooding, particularly during winter and spring, is likely to be substantially more severe than at present, especially in colder years when above-normal snowpack develops.
• Increased evaporation and plant transpiration and dryer soils in the summer, resulting in less water available to nourish wetlands, provide stream flow, and keep our lake levels high.
• Drought and a greater risk of forest loss due to insects and diseases as well as from forest fires.
• Lakes will be ice-free for longer (later freeze over and earlier ice melt), warm up more during the ice-free season, and be at greater risk of deteriorating water quality.
• Algal blooms will be more frequent and there will be changes in the ecology of our lakes and in the composition of aquatic species.

The above findings from the MWC report did not specifically identify the likelihood of more intense precipitation events that have the potential to cause significant runoff and accelerated leaching of algal-friendly nutrients, but these findings have been identified in other studies. More recent work in Ontario also has now identified reduced wind speeds during the summer months as another meteorological variable associated with our changing climate and this may be one of several causal factors related to increased numbers of harmful algal blooms as low wind speeds combined with increasing water temperatures result in very favorable conditions for accelerated algal growth.

Water Temperature Changes in Kahshe and Bass Lakes

As shown in the charts below, the late-season (summer) records of water temperature at increasing depths at mid-lake locations in both lakes have not identified any long-term trends in water temperature.

However, using larger data sets from many Muskoka lakes, the Environment Ministry has demonstrated that a water temperature increase is happening. As such, the KLRA plans to continue assessing whether there are any potential impacts on lake water quality and the health of our aquatic and terrestrial resources. These are discussed more thoroughly in the annual Lake Steward reports.