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The most reliable indicators of climate change are temperature records. Weather stations around the world are regulated by the World Meteorological Organization. This organization makes sure temperatures are measured at the same time of day, using the same instruments, at a fixed height above the ground, by trained observers.

To accurately calculate Earth’s average temperature, scientists take into account any abnormalities at weather stations that would cause jumps or false trends in the record. Scientists then average together all the information they have to get a global picture of what Earth’s temperature has looked like each year from today back to 1850, the first year there were enough stations to calculate a global average.

From these observations, we see two things. First, there is considerable variability from one year to the next. That’s weather. Second, there is a steady, long-term trend over the entire century. That’s climate.

Global temperature has increased by 1.3°F since 1900. Out of nearly 160 years of records, the ten warmest years have all occurred since 1997.

Average temperatures across the United States and Canada have risen even faster than the global average, more than 2°F since 1950. In the western and northern United States, temperatures have risen on average 70 percent faster than the global average; in some parts of Alaska, by as much as 4°F.

Here’s what the global temperature record looks like:

The calculation of Earth's average temperature is based on observations from thousands of locations around the world. Here, temperature changes are shown relative to the global average temperature for the period 1961-1990. Over the last century, global average temperatures have risen steadily despite year-to-year variations.

And here’s where you can get the data for yourself, from the U.K. Meteorological Office.

Want more? The American Institute of Physics explains the history of temperature over the lst century.