Climate change is a common topic of conversation these days. One manifestation of climate change is temperature, and one way to look at temperature trends over the long term is to examine decadal trends. Decadal averages help smooth out the annual variations in temperature and make trends more apparent. Environment Canada makes this easy to do as they provide homogenized data sets for various locations across Canada. These data are calibrated to account for instrument and related changes (see documents in the above link for procedures used).The EC datasets can readily be imported into spreadsheets and decadal averages calculated.
In the chart below, I have calculated decadal averages for all decades (1800s through 2010) for Moncton, Saint John, Fredericton, Bathurst and Chatham/Miramichi. The decadal averages were calculated by averaging the annual mean temperature. The following chart shows all available decadal data (i.e. I’ve omitted decades where data for more than three years of the decade were not available). For some locations, this means we can look at data from the late 1800s. On the other hand, some data are missing from some locations. I refer those interested to the technical reports cited at the EC site for explanations re the effect on data arising from temperature instrument changes, etc, on data quality.
As you can see, the average temperature for each decade has increased at each location over time. The increase in mean annual temperature over the last four decades was 0.9 C for Moncton, 0.6 C for Bathurst, 0.8 C for Fredericton, 1.0 C for Chatham/Miramichi, and 1.1 C for Saint John.
For comparison purposes, the International Panel on Climate Change has calculated that, globally, the rate of surface temperature change was 0.177 C per decade over the past 25 years and 0.128 over the past 50 years. If you multiply those values by 4 (to represent the past 4 decades), you can see that New Brunswick is following the global trend towards warmer annual temperatures.
Where 10 years (the complete decade) of data are available, the average is the mean of those 10 years; where 2 or 3 years of data are not available (because they don’t exist for some reason , or did not meet EC/WMO quality standards), then the average is the mean of those remaining 7 or 8 years. Data from decades with more than three years of data missing are omitted.
A trend of increasing temperature is observed in most locations; Saint John, however, shows a lot more ‘wobble’ than other locations. Note that in most locations, the 1950s seems to have been a particularly warm decade, compared to its nearest neighbours. The most recent decade (2001-2010), however, has been the warmest to date by a significant margin.
Temperature changes over the span of temperatures shown above were calculated simply by subtracting the mean for the first decade from the mean of the last decade. Over the range of locales analyzed, mean temperature increases per decade ranged from 0.14 to 0.25 C. For most locations, that’s a lower rate of increase than over the past four decades alone.
I’d also like to recommend the Wunderground site where data from Maine and other US locations can be viewed. You will see similar trends in Maine to what we see in NB. A good analysis of regional and national temperature trends in Canada can be found here.
[update – seasonal decadal trends for New Brunswick regions can be found here ]
Atmospheric concentrations of CO2, thought by most climate scientists to be one of the main drivers in global temperature, increased slowly from the mid-1800s until the 1950s/60s period. Around that time, CO2 concentrations began to rapidly increase. That would suggest we will see further temperature increases in decades to come. On the other hand, elevated concentrations of sulfur dioxide from industrial activity or volcanoes would suppress the response to CO2. Sulfur dioxide, for example, is thought to have contributed to the observed cooling during the 1960s. In other words, CO2 is not the only driver of climate change; it is just that rising CO2 levels have made it the dominant driver over the past several decades.
Surface temperature datasets have been found to be reliable and well-correlated to satellite temperature data, especially for the northern parts of the globe (such as NB). Note that air temperatures are not the whole story; ocean temperatures also contribute to warming trends.