Global Average Near-Surface Temperatures—Monthly Anomalies (1961–2002)

Measuring climate change is more difficult than simply taking measurements of weather phenomena at one time and place. Climate refers to overall, long-term weather patterns, so understanding climate change involves combining many different measurements. For example, climate researchers can compare changes in a measured global temperature each year with the normal temperature, or long-term mean, averaged over prior years.

This graph shows near-surface atmospheric temperature anomalies—differences between the average measured global air temperature and the long-term mean. These data come from many instruments on land, ships and buoys, and satellites.

Discerning a trend between 1961 and about 1977 is difficult: Sometimes the average global temperature was above normal, sometimes below. This is not surprising, because temperature is inherently variable—short-term fluctuations are not unusual. But most anomalies since 1977 have been above normal—warmer than the long-term mean. The latest averages indicate a global temperature increase of around 0.7ºC. This might seem small, but the complexity of the climate means that even small deviations can have major effects.