Overview of Climate Change in Muskoka

By: Ron Pearson

Kahshe and Bass Lake Steward

December 2020

For the Record…

Let’s be clear from the start. I am not a climate research specialist, so the summary information that follows is based totally on my review and understanding of the scientific literature I’ve cited. That said, my science training and over 40 years of employment in environmental biology has given me a broad understanding of how long term changes to aquatic and terrestrial ecological systems can manifest in response to anthropogenic stressors and of how these types of changes can form the basis for projected future outcomes. However, my experience tells me that we must always think critically about the scientific analyses presented and the assumptions upon which they are based, particularly when trying to project beyond the present to future outcomes.

What’s in this overview and how was it developed?

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, as well as its people.  These potential impacts are described in reports released by the Muskoka Watershed Council (MWC) (2016), United Nations Intergovernmental Panel on Climate Change (IPCC, 2018), and the Government of Canada (2019).

The 2016 MWC study and the additional summary documents are linked or attached as PDFs in this section and are cited below as recommended reading for anyone who wants to better understand how projected changes in our climate may unfold.  For a more thorough assessment and discussion of the climate change literature and additional detail on how the projected changes could affect our own lakes as well as a more detailed examination of what the KLRA is doing to monitor these impacts, the reader is referred to the document titled: Climate Change – Impacts on Kahshe and Bass Lakes (click here).

Background Information about climate change science

Before proceeding further, it’s important to understand how the IPCC was formed and how it functions, as the findings from this global agency form the primary foundation of all the material that follows. Here’s a brief description of the IPCC.

The Intergovernmental Panel on Climate Change (IPCC) is an international body responsible for assessing the science related to climate change. It was set up in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to provide decision-makers with regular assessments of the scientific basis of climate change, its impacts and future risks, and options for adaptation and mitigation. The assessments are undertaken and presented in a way that is relevant to policy but not prescriptive of any specific policy.

The IPCC is both scientific and governmental in nature. IPCC assessments are written by hundreds of lead and supporting scientists who volunteer their time and expertise as authors of these reports. IPCC reports undergo multiple rounds of drafting and are independently reviewed by hundreds of both scientific experts and governments to ensure they are comprehensive and objective, and are produced in an open and transparent way.

As the science of climate change is complicated and involves making many input assumptions and utilizing large scale climatic and meteorological datasets, there are some who question the authenticity of the underlying data and the modelling of projected outcomes based on the climate monitoring database. Others have explored the reasonableness of the assumptions that have been made in estimating emission reduction scenarios that form the basis for the projected outcomes. Based on some feedback within the KLRA’s Conservation Committee, this overview document has been modified from the version posted in November to reflect the findings from more recent studies, including a 2019 Government of Canada report.

What is climate change and what is driving it?

The reports cited above project the likelihood of future changes in temperature, precipitation, and storm events by examining greenhouse gas emissions under several different carbon emission reduction scenarios. 

They tell us that emissions from burning fossil fuels are causing increased concentrations of greenhouse gases in our atmosphere.  High levels of greenhouse gases are driving temperature increases, which in turn drive other changes.  It follows, then, that reducing emissions of carbon dioxide (CO2) and other greenhouse gases will slow down the rate of climate change.

How much will the climate change?

It depends on what we do to reduce accumulation of greenhouse gases in the atmosphere.  Table 1 describes two scenarios that were evaluated in the 2016 MWC report.

Table 1 Select climate change scenarios from MWC 2016 Report

Climate Factor

Greenhouse Gas Emission Reduction Scenario RCP8.5

a scenario (often termed ‘business-as-usual’) in which we continue to use fossil fuels as the primary source of energy for our economy

Greenhouse Gas Emission Reduction Scenario RCP4.5

a scenario in which the global community makes a sufficient change to its fuel sources to the extent that we limit warming of global mean temperature to 2oC by 2100.


  • Average daily mean

3-4°C warmer each month

2-3oC warmer each month

  • Summer (May to September)
  • 7-times more summer days above 30°C
  • Monthly mean temperature increase of 3.4°C
  • Increase in number of summer days above 30°C not shown
  • Monthly mean temperature increase of 2.5°C
  • Winter
  • 64% more winter days above freezing
  • % of winter days above freezing not shown


  • Overall 10% increase in precipitation
  • Shift towards 17% more precipitation from late fall to early spring and similar or somewhat less precipitation through summer and early fall
  • % increases not shown

Storm Events

  • Fewer, but more pronounced storm events with precipitation deluges and high winds.
  • Not shown


1.      RCP stands for Representative Concentration Pathway.

2.      Projected changes (compared to historical climate records for the period from 1971-2000) in the climate of the Muskoka area by mid-century (2041-2070).

3.      A third, more aggressive emission reduction scenario (RCP2.6) which would be required to limit average global warming to 1.5°C was not included in the projected temperature increases, as there was no convincing evidence that world leaders were committed to meeting this goal.

What are the potential impacts?

Based on the information I have examined, the RCP scenario likely to best represent emission reduction reality and future temperature increases for the months most relevant to recreational users of the lake would be the RCP4.5. More recent findings have indicated that the RCP8.5 scenario should be considered as a worst-case emission scenario, and not referred to as business-as-usual, as the progress that has already been made in global emission reduction already exceeds the emissions that underpinned the model projections using RCP8.5.

From the MWC’s modelling, a projected mid-century temperature increase for the months of May through September appears to lie somewhere around 2.5oC. 

The more recent 2019 Government of Canada document provides some additional projections for average annual temperature increases in Ontario for three 20-Year periods through to the end of the century. As for the earlier MWC report, these increases are projected under an RCP4.5 emission reduction scenario (medium level of carbon emission reduction). The values presented are for the 50th percentile of 29 CMIP5 model runs with the bracketed values shown for the 25th and 75th percentiles. The increases in temperature are based on comparisons to a reference period of 1986-2005.






1.3 (0.8-1.6)

2.4 (1.8-2.8)

3.2 (2.3-3.8)

These findings are essentially the same as those projected for this emission reduction scenario earlier in the 2016 MWC document.

The potential impacts of these changes in temperature and precipitation are projected to 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 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.

While it is difficult to identify statistically significant climate changes and their potential impact on water quality of Kahshe and Bass Lakes due to the limited sampling and analysis history and the small sample size, the KLRA is actively monitoring changes in climate to assess whether there is any potential impact on lake water quality. As noted earlier, these findings have been discussed in a separate document titled: Climate Change – Impacts on Kahshe and Bass Lakes which can be viewed by clicking here.

References Cited

Peter Sale, Richard Lammers, Norman Yan, Neil Hutchinson, Kevin Trimble, Paul Dinner, Piret Hurrell, Jan McDonnell, and Scott Young. 2016. Planning for Climate Change in Muskoka. A Report from the Muskoka Watershed Council. Muskoka Watershed Council, Muskoka, Canada, 52 pages.

Hoegh-Guldberg, O., D. Jacob, M. Taylor, M. Bindi, S. Brown, I. Camilloni, A. Diedhiou, R. Djalante, K.L. Ebi, F. Engelbrecht, J.Guiot, Y. Hijioka, S. Mehrotra, A. Payne, S.I. Seneviratne, A. Thomas, R. Warren, and G. Zhou, 2018: Impacts of 1.5ºC Global Warming on Natural and Human Systems. In: Global Warming of 1.5°C. An IPCC Special Report. [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I.Gomis, E. Lonnoy, T.Maycock, M.Tignor, and T. Waterfield (eds.)]. In Press.

Bush, E. and Lemmen, D.S., editors. 2019. Canada’s Changing Climate Report; Government of Canada, Ottawa, ON. 444 p.

Ontario Centre for Climate Impacts and Adaptation Resources (OCCIAR) and Ontario Ministry of Natural Resources and Forestry (OMNRF). 2017. Workshop Report – A Workshop on Extreme Weather and Waterfront Property. 2017. 38 pages.

Muskoka Watershed Council. 2018a. Report Card on Climate Change in Muskoka. 10 pages. Web-based HTML document converted to Word and saved as PDF.

Muskoka Watershed Council. 2018b. Brochure 1. The New Muskoka Climate. Muskoka, Canada. 1 page.

Muskoka Watershed Council. 2018c. Factsheet 1 – Planning for Climate Change in Muskoka. The New Muskoka Climate. Muskoka, Canada. 2 pages.

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