In terms of a temperature trend over the past 50 to 100 years, average annual temperatures seem to have increased slightly at a half dozen climate stations that were examined in Alberta. The degree of change is not consistent across the province, with some places recording negligible positive trends while a few others have had increases of up to 2°C in their mean annual temperature. Northern locations appear to be more affected than those in southern Alberta. As well, the amount of temperature increase is not occurring evenly over the whole year; rather, it appears to be mostly seasonal in nature. Relatively small changes are being observed in summer temperatures. Most of the change can be attributed to warmer winters. At this time, given limitations of data records and our understanding of climatic processes, it would be speculative to attribute these changes to either natural or human-induced factors, or a specific combination of these.

The following air temperature plots are taken from three locations in Alberta: Fort McMurray, Grande Prairie and Lethbridge. The first graph for each site shows the annual temperature deviations from the long-term average for that site over time. Essentially, it depicts how different each year was when compared to average. Bars that are above the red line show the year was warmer than average, while bars below the red line indicate it was cooler than average. This is where some see a possible trend in more recent years in that there has tended to be more above-average years. This represents a small sample of sites and the trend is not necessarily strong or uniform. Additional study is needed. The second plot for each site shows how the winter and summer temperatures compared to the winter and summer average over the past twenty years. All three sites show a strong indication that, at least over the past twenty years, the winters have tended to be slightly warmer while the summer temperatures do not appear to have changed very much.

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Fort McMurray

		Temperature deviation from mean					Seasonal temperatures

Grande Prairie

		Temperature deviation from mean					Seasonal temperatures

Lethbridge

		Temperature deviation from mean					Seasonal temperatures

Selection of study sites is important to make reasonable interpretations of the data. Obviously, the longest possible continuous records are an important consideration. However, the long-term data at Edmonton and Calgary, for example, may not be suitable for trend analysis as these climate stations are located in the middle of large cities and are subject to a "heat island" effect. As the cities have grown, the amount of waste heat produced by various activities has increased. As a result the temperatures in the cities tends to be one or two degree higher than the surrounding areas, although the effect is much more noticeable in the winter. Use of such data must be carefully considered as it could lead to an incorrect determination of a temperature trend that may be related only to an artificial local-scale phenomenon.

To read about whether climate change may be influencing water quantity and water supplies in Alberta, click on recent water quantity trends.