Additional info from the National Oceanic and Atmospheric Administration
Common Questions About Weather Observing Stations
Could weather stations located in potentially warmer locations near buildings and cities influence temperature readings?
Yes. That is one reason why the National Oceanic and Atmospheric Administration (NOAA) created the Climate Reference Network. These stations adhere to all of the established monitoring principles and are located in unpopulated areas. They are closely monitored and are subject to rigorous calibration procedures. NOAA’s National Climatic Data Center also provides data checks of the measurements, looking for discrepancies. These efforts ensure the temperature readings are reliable.
Does a station near a building or a city record warmer temperatures than a station in an unpopulated area?
Not necessarily. Many local factors influence the observed temperature: whether a station is in a valley with cold air drainage; whether it’s a liquid-in-glass thermometer in a standard wooden shelter or an electronic thermometer in the new smaller and more open plastic shelters; whether the station reads and resets its maximum and minimum thermometers in the coolest time of the day in early morning or in the warmest time of the day in the afternoon; etc. But for detecting climate change, the concern is not the absolute temperature — whether a station is reading warmer or cooler than a nearby station placed on grass — but how that temperature changes over time.
Is there any question that surface temperatures in the United States have been rising rapidly during the last 50 years?
No. Even if NOAA did not have weather observing stations across the United States, the impacts of the warming are clear and present. For example, lake and river ice is melting earlier in the spring and forming later in the fall. Plants are blooming earlier in the spring. Mountain glaciers are melting. Coastal temperatures are rising. A multitude of species of birds, fish, mammals and plants are extending their ranges northward and, in mountainous areas, uphill toward cooler areas.