A Primer on Climate Change for Peterborough

The Earth is surrounded by a thin layer of gases, held close to the Earth by gravity. The main gas causing climate change is carbon dioxide (CO2) even though it comprises only 0.04% of these gases, because its concentration is changing rapidly. The CO2 concentration is also often given as “parts per million” or ppm. It was close to 250 ppm for the last 800,000 years, but this has risen dramatically with burning of large amounts of industrial fossil fuels and reached 405 ppm in 2017, the highest in more than 300 million years.

About 71 percent of the coming solar energy is absorbed by the Earth system (its atmosphere and the Earth itself) and the rest is reflected back into space. Greenhouse gases (GHGs) such as water vapour, ozone, CO2, methane, and nitrous oxide are all responsible for absorbing part of the reflected energy, much as greenhouse glass traps heat from the solar radiation that penetrates the glass. These GHGs have served to warm the Earth’s atmosphere enough to make it liveable for modern humans who appeared about 350,000 years ago. However, even relatively small changes in the quantity of GHGs can change the average global temperature, and this is what we are seeing with the rapid human-caused increase of atmospheric CO2, and of methane to a smaller extent.

The average global temperature has risen about 0.8 °C since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20 °C per decade. Canada has warmed an average of about 1.5 °C, although the increase varies strongly from region to region. The IPCC (Intergovernmental Panel on Climate Change) has said that dangerous climate change occurs at global increases of about 2 °C, but serious effects occur at lower temperatures.


  1. The number of days over 30 °C in Peterborough has increased significantly, from about 6 days per year 30 years ago to 23 in 2018. Any human is at risk of dying for extended periods near 45oC, and the elderly and young suffer at lower temperatures.
  2. The quantity of water vapour that the air can hold increases about 7% for each degree Celsius increase in temperature, causing much more severe rainfall and flooding.
  3. At the same time, warm air can absorb more water from the soil and vegetation, leading to droughts and
  4. more severe forest fires.
  5. Global temperature differences drive the “polar vortex” which confines weather patterns in North America. The polar vortex is weakened under climate change, resulting in more extreme hot and cold weather events.
  6. The nutritional value of food and the quantity produced both decrease with high temperatures.
  7. Worker productivity decreases at high temperatures, and absenteeism increases.

A recent scientific study in the Proceedings of the National Academy of Sciences USA states that the world must dramatically reduce its greenhouse gases (GHGs) in as little as 10 years to avoid unstoppable climate change that will make the world uninhabitable for humans for thousands of years.

A second study, by the Global Commission on the Economy and Climate, shows that acting aggressively to reduce greenhouse gases within the next three years will generate a $26 trillion economic global windfall, create 65 million new jobs, and avoid 700,000 early deaths linked to air pollution.

How can we reduce climate change and improve the economy?

We must reduce GHG emissions rapidly to avoid the worst effects and reap the economic and health advantages. Peterborough City and County Climate Change Action Plan (CCAP) provides a blueprint for reducing our GHGs by typically 30% below 2011 levels by 2031. (See SustainablePeterborough.ca and look under “Projects”.) This requires no new technology; just the political will to act. For example, 39% of the City’s GHGs come from home heating. The CCAP calls for retrofitting 40% of existing houses by 2031 to make them more energy-efficient, or some 700 houses per year for 13 years. Think of the number of jobs and the boost to the economy! Moreover, every $1 spent today saves $38 in future costs.

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