Monthly Temperature Anomalies Versus El Niño

The graphic below depicts the monthly global temperature anomalies—that is, each month compared to its 20^th century average—since 1950, and the influence of the El Niño - Southern Oscillation (ENSO) phenomenon.

The height of the bar represents the global temperature anomaly for the month. The color of the bar represents the ENSO status, defined by the Oceanic Niño Index (ONI), which is the three-month average temperature anomaly in the Niño3.4 region centered on that month. Months colored in red had ONI values indicating an El Niño episode active (at least five consecutive months with the three-month Niño 3.4 temperature more than 0.5°C [0.9°F] above the working "normal"). Blue represents La Niña episodes, more than 0.5°C (0.9°F) cooler than normal. Months in grey indicate ENSO-neutral conditions, when neither El Niño nor La Niña were present.

Several observations are apparent in the figure. First, nearly every month since the late 1970s has been above the 20^th century average, and has generally warmed through the period. Second, El Niño-like conditions (those months in red) tend to be warmer than neighboring periods, and La Niña-like conditions (blue) tend to be cooler. Third, protracted El Niño-like episodes tend to warm through the event, while La Niña-like episodes tend to cool through the event. Fourth, and finally, there are exceptions to all of the above points.

Global monthly temperature anomalies, with ENSO status