(Click here for Talk.) We have examined archival records of temperature, relative humidity, precipitation, pressure, wind etc. These measurements were made on an hourly or daily basis at over 75 airports located throughout Canada during the last 55 years. The data is first searched for sudden discontinuities caused by changes in measurements procedure and/or instruments. One then applies statistical tests to search for significant changes in climate. Most recently, we examined over a ¼ billion hourly temperature and humidity measurements made in North American during 1948-2010. The results show there has been a 5o C warming affecting primarily Western Canada and the Mackenzie River Basin.
We have also investigated a claim made that the suspension of commercial flights over North America for 3 days following the tragic events of Sept. 11, 2001 changed the diurnal temperature range (DTR) due to the absence of airplane contrails. Hourly data was observed at 288 stations was examined. The average DTR, temperature, maximum/minimum temperature and relative humidity were found for each day in 2001 and compared to the average value occurring during 1975-2005. For the coterminous U.S., the DTR averaged over the period Sept. 11–14, 2001 was about 1°C larger than that found for the 3 days prior and after the flight ban. However, the day-to-day DTR does not correlate well with the flight ban. Plots of the change in DTR throughout North America during Sept. 8–17 show changes consistent with the natural progression of weather systems.