Measuring the climate

Hourly weather conditions and other climate-related data are recorded at weather observing stations around the world. Satellites, weather balloons and other types of instruments also observe weather conditions. Daily observations may include:

  • total rainfall
  • total snowfall
  • total precipitation
  • amount of snow accumulation on the ground
  • maximum temperature
  • minimum temperature

Data from these stations’ records, averaged over many years, form one type of observed climate record. The period used for averaging is called a reference period and often covers about 30 years. The period often starts at the beginning of a decade. Monthly and annual climate averages (and other statistics) calculated using reference periods (for example, 1971 to 2010) are known as Climate Normals.

Figure 1: Automated weather station: Lansdowne House reference climate station

Automated weather station located in Lansdowne House, Ontario.
Long description

This photo of a weather station in Lansdowne House, Ontario contains a small, white building, which houses a data logger and barometric pressure sensor for this station. There is a small box with slatted sides called a Stevenson screen, which contains instruments for measuring temperature, dew point, and humidity. There are three pole shaped wind sensors with instruments on the top, two of which are 10 meters tall, and the third is two meters tall. These sensors measure wind speed and direction. There are two small precipitation gauges. One is an all weather gauge and the other is a tipping bucket gauge. Finally, there are three snow depth sensors as well. The station is located on a patch of gravel in an open, grassy area.

Weather station observations often cover very long periods, much longer than the 30 years commonly used as a reference period. Many other types of observations, especially satellite observations, are not available for such long periods.

Canada’s climate record started in 1840 with the archiving of basic weather information. Observed climate data are available for most parts of southern Canada from 1900 onwards. For the rest of Canada, observed climate data availability gradually increases from 1913 until after 1950. Daily climate data beginning in 1870 and hourly weather observations beginning in 1953 are available online.

Over the years there have been changes to the way the weather information has been collected.  This can make it challenging to compare the data. For example, stations are moved, the measuring instrument changes, or the urban landscape around a station changes. Climate scientists adjust some observed datasets to account for these changes and to make sure they’re comparable. This procedure is very important for looking at long term changes in climate.

Observed climate data can be provided as point data (each point represents a weather station) or on regularly gridded cells. Like future climate projections, gridded data covers the entire country. To produce these regular grids, conditions at locations between the actual stations are estimated using information from nearby stations.

Explore observed climate data in the library of climate resources or view observed climate data on a map.

Related links

  • Charron, I. 2016. A Guidebook on Climate Scenarios: Using Climate Information to Guide Adaptation Research and Decisions. Montreal, QC: Ouranos.
  • Environment and Climate Change Canada. 2017. Climate data and scenarios: synthesis of recent observation and modelling results. Government of Canada.
  • Hausfather, Z., Cowtan, K., Menne, M. J., & Williams, C. N. 2016. “Evaluating the impact of US Historical Climatology Network homogenization using the US Climate Reference Network.” Geophysical Research Letters 43, 4: 1695-1701.
  • Mekis, É. and L.A. Vincent. 2011. “An overview of the second generation adjusted daily precipitation dataset for trend analysis in Canada.” Atmosphere-Ocean, 49, 2 : 163-177.
  • Vincent, L. A., X. L. Wang, E. J. Milewska, H. Wan, F. Yang, and V. Swail. 2012. “A second generation of homogenized Canadian monthly surface air temperature for climate trend analysis” J. Geophys. Res. : 117.
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