The Greenhouse Effect and Crop Heat Unit Trends in Northern Ontario

Climate and Change

While weather is based on short term measures of atmospheric conditions such as temperature, precipitation and cloud cover, climate refers to the long term averages for these factors. Since the weather is quite variable on a day to day basis, it can be difficult to detect long term trends without utilizing accurate, long term records. Scientists who study the long term patterns in climate (climatologists) have found that overall, the earth's climate has warmed since the early 1900s, with some dips in the overall trend. The consensus of climatologists is that the average temperature of the earth (lower atmosphere) has risen by 1.4° F. in the last hundred years. While this may not seem like a lot, it can have a big impact on the length of the growing season and the heat available to stimulate plant growth.

Why is It Getting Warmer?

This warming trend is associated with a steady increase in the amount of carbon dioxide (CO2) (and some other gases) in the atmosphere. When energy from the sun's rays strikes the earth's surface, some of the energy which is initially absorbed by the earth is emitted back into the atmosphere in a form which can be absorbed by these gases. Higher levels of these gases results in more of this energy being trapped instead of being lost into space, warming the atmosphere. This is called the "Greenhouse Effect", and the gases are called Greenhouse Gases (GHG). And since the level of GHG is expected to keep rising, it is predicted that average temperatures will continue their upwards trend for at least the next 100 years.

How Does Climate Change Affect the North?

In general, the magnitude of the temperature change associated with the Greenhouse Effect increases with distance from the equator. This has been evident in the dramatic decreases in the amount and duration of seasonal ice cover in the Arctic. Northern Ontario's agricultural regions, at about 46 to 49° latitude (N) lie in the temperate zone, a little over halfway between the equator and the north pole. At this latitude, the effects of climate warming would be expected to be significant. And since crop production in this region has traditionally been hampered by a short, cool growing season, even modest increases in heat could result in significant benefits.

In order to evaluate the impact of climate warming across Northern Ontario, Crop Heat Unit (CHU) data from five locations across the North were reviewed and graphed to determine trends over time (Figure 1). Crop Heat Units are a good measure of the growth and maturing potential of warm season crops such as corn and soybeans. The data for North Bay, Sault Ste. Marie and Kapuskasing covered the past 50 yrs., while data for Thunder Bay and Rainy River included only the past 16 yrs.

Arial map of Great Lakes area with yellow push pins showing locations of cities.

Figure 1. CHU Data Collection Locations

Both Kapuskasing and North Bay displayed a consistent positive trend, with CHU increasing significantly over time. For Kapuskasing, the rate of increase was 117 CHUs per decade (Fig. 2). From 1965 to 2005, seasonal CHUs increased from approximately 1650 to 2150.

Line graph with years along the bottom from 1960 to 2010. Crop Heat Units are listed along the left from 1600 to 2200. A straight line is drawn from the bottom left to top right.

Adapted from Bootsma, A., 2013. Eastern Cereal and Oilseeds Research Center, Ottawa. Final Report, 2013

Line graph with years shown from 1960 to 2010. Crop Heat Units are listed from 2200 at the bottom to 2800. A straight line is drawn from the bottom left to top right.

Adapted from Bootsma, A., 2013. Eastern Cereal and Oilseeds Research Center, Ottawa. Final Report, 2013

The trend for North Bay was an increase of 100 CHU per decade, going from approximately 2300 to 2700 CHU from 1965 to 2005 (Figure 3).

Sault Ste. Marie CHUs show a different pattern, exhibiting a trend which had little change in CHUs from 1965 to 1985, followed by a sharp increase from 1985 to 2005 (Figure 4). The rate of increase from 1985 to 2005 was approximately 130 CHU per decade.

Line graph with years from 1960 to 2010. Crop Heat Units are listed along the left side starting at 2250 to 2600. A curved line starts at the bottom left corner sloping up to the top right.

Adapted from Bootsma, A., 2013. Eastern Cereal and Oilseeds Research Center, Ottawa. Final Report, 2013

In contrast to the other 3 stations, data from Thunder Bay and Rainy River showed no significant change in seasonal CHU from 1997 to 2013 (Figures 5 and 6).

Line graph with years 1995 to 2015 listed. Crop Heat Units are listed along the left side from 500 to 3000 at the top. A straight row of blue diamonds are clustered between the 1500 line and the 2500 line.

Based on data from Thunder Bay Agricultural Research Station.


Line graph with years from 1995 to 2015 on the right. Crop Heat Units start at 0 and go to 3000 at the top. A straight row of blue diamonds are clustered between the 2000 line and the 3000 line.

Based on data from Emo Research Station.

The increase of 300-400 heat units at Kapuskasing, North Bay and Sault Ste. Marie have had a significant effect on the yield of and type of crops which can be grown at these locations. For example, canola is now grown in the Kapuskasing area, while grain corn and soybeans are part of cropping systems in the New Liskeard area. This is contrast to a couple of decades ago, when field crops in these areas were dominated by cereal grains such as barley and oats. Surprisingly, the two stations in the Northwest have not experienced any change in CHU over the past 15 years.

Why the Differences Between Northwest and Northeast Locations?

Hudson's Bay exerts a large cooling effect on the climate of Northeastern Ontario, with the effect increasing the closer a location is to the Bay. The Bay freezes over in the winter, creating a light coloured surface that reflects a lot of solar radiation, leading to colder air temperatures, and forming mass of ice which takes a long time to melt in spring, slowing the advance of spring. However, the ice free period on Hudson's Bay has increased steadily during the last several decades, with the ice forming later in fall and melting earlier in spring. This has had a warming effect on the surrounding landscape due to a shortening of time during which the "refrigerator effect" is happening, and by increasing the length of time the darker (ice free) water surface is available to absorb solar radiation. As well, the Bay is a relatively shallow body of water which heats up more quickly than a deeper body of water would.

Since Kapuskasing is much closer to Hudson's Bay than the other stations, it has likely experienced a greater effect from changes in ice cover in the Bay than the other locations. North Bay is likely influenced to a weaker extent by Hudson's Bay. Sault Ste. Marie presents an interesting case, located close to three Great Lakes. They may be responsible for moderating the climate from 1960 to 1980, when the earth's overall warming trend overcame that effect, with warming then occurring at a rapid rate up to the present. Thunder Bay is located on Lake Superior, a large volume of cold water which would tend to slow the impact of any global temperature increase. Rainy River is located far from Hudson's Bay and relatively far from Lake Superior. The reason for it experiencing no change in annual CHUs, compared with the increases in the Northeastern locations is not clear.

Based on the data reviewed for this article, the growing conditions in Northeastern Ontario have improved markedly over the last 30-40 years, resulting in improved crop yields and widening the array of crops which can be grown. In contrast, Northwestern Ontario locations have not seen any change in growing conditions over the shorter time frame for which data was available.

i Pearson, David. Climate Change in Northern Ontario. Kapuskasing Agricultural Symposium, 2013.

Thanks to Rudy Buitenhuis, OMAF and MRA for Thunder Bay and Rainy River data.

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