claim: Two American researchers allege that U.S. government scientists have  skewed global temperature trends by ignoring readings from thousands of  local weather stations around the world, particularly those in colder  altitudes and more northerly latitudes, such as Canada.
evidence: Human activities, primarily the burning of fossil fuels (coal, oil, and natural gas), and secondarily the clearing of land, have increased the concentration of carbon dioxide, methane, and other heat-trapping ("greenhouse") gases in the atmosphere...There is international scientific consensus that most of the warming observed over the last 50 years is attributable to human activities.