Data from my weather station for the period 1997-2020 is compared to Environment Canada’s data from 1914-1983. While the analysis is strongly indicative of a global warming trend in Tobermory, the short time span (24 years) of recent data and the slight differences in location and methodology prevent any absolute conclusions to be drawn. The data do support the claim of many Global Circulation Models that winter temperatures will show a greater departure from the long-term norms than summer temperatures do.
Locations and Observing Procedures.
My station (hereafter “Big Tub Station”) is located at 45°15’28”N, 81°40’14”W on Big Tub Harbour, approximately 40 meters from Lake Huron at an elevation of about six meters above the lake surface. It has operated continuously since late 1996, downloading data to my computer every hour.
Environment Canada’s (“EC’s”) station was located at 45°15’21”N, 81°39’42”W (Bay St. South) approximately one kilometre east of Big Tub Station, but essentially the same distance and height from Lake Huron. Its records run from 1914 to 1983, when it was moved to Cyprus Lake and then more recently to Tobermory Airport. Records since 1983 have been ignored as the latter locations represent quite different microclimates. EC’s daily data were read twice daily by a human observer and recorded manually.
Both stations are/were mounted 1.5 meters above ground in louvered shelters. Big Tub Station uses electronic components to measure temperature; as such components are subject to “drift” over time. They are checked against a calibrated reference (mercury) thermometer every few months and adjusted. In practice the need for this has been quite rare and the adjustments less than 0.2°C.
Generally climatologists consider 30 years to be the minimum length of a record to be statistically viable. Big Tub’s record is only 24 years and thus is not as reliable as a longer record. The difference, however, is unlikely to be significant.
Although the locations of the two stations used in this analysis are very close and similar in terms of surrounding topography, they are not the same and may have some small microclimatic differences.The methods of establishing means are also different. Big Tub Station averages the 24 hourly readings taken each day, whereas EC took the high and the low for each day, just two figures, and averaged them. A comparison of the two methods reveals no meaningful difference in the results. The Data. Summarized below are the data from the two stations. All figures are in degrees Celsius. The chart shows the mean temperatures by month and year for Big Tub Station and the mean for the 24 years 1997-2020, using the integration (24 readings a day) method. The EC means are for the period 1914-1983; the difference between the two stations is recorded on the bottom line. With the exception of April, which is a wash, every month shows Big Tub’s 21st century temperatures are warmer than those of Environment Canada in the 20th century. The greatest differences occur in the winter month, as most Global Circulation Models have predicted.As can be seen, December, January and February are distinctly warmer than in the last century. This is corroborated by subjective observations from local residents – there are now few really cold days in the minus 20°C range. In addition, species of birds and animals hitherto not seen this far north of Lake Erie are spreading throughout the region. Snowmobile trails open later and close sooner than they used to.There are two anomalies observed. Until 2018, April showed a smooth transition from March’s delta of +1.01° to May’s +0.25° An unusually frigid April 2018 contributed to the 24 year average being lower than might be expected. The other anomaly occurs in September which is higher than the trend would lead one to expect. This cannot be laid at the feet of a single warm year – nearly all Septembers this century show warmer weather than the EC figures. This has been discussed with a senior EC climatologist who has seen this anomaly elsewhere. There is presently no explanation, though it is possibly an effect of the lake water temperature. Warmer years may be heating the water up just enough in the summer to maintain temperatures even as the year begins to cool off.
Despite the caveats at the beginning of this paper, the conclusions mesh with those that climatologists are seeing world-wide. NOAA reports that global temperatures this century have risen by 0.95°C over the 1900s. Tobermory certainly seems representative of that increase, especially when one considers that the most warming is occurring at the Poles rather than our mid-latitudes. The findings are consistent with the bigger picture.