1. El Niño-Southern Oscillation
El Niño-Southern Oscillation—Seasonal to Interannual Climate Changes
Not all climate changes are on decades to centuries time scales.
Scientists have recently learned to predict seasonal climate changes associated with annual changes in the El Niño-Southern Oscillation (called ENSO).
El Niño refers to above-normal sea surface temperatures that typically appear around Christmastime in the Eastern Pacific Ocean. Fishermen of Ecuador and Peru named it El Niño, which means “the little boy” or “the Christ Child.” The opposite, below-normal sea surface temperatures,is referred to as La Niña.
During El Niño years, the easterly winds that blow across the Pacific weaken and no longer cause cold water to rise to the surface. This ocean-atmosphere interaction affects weather around the world.
The record-breaking El Niño in the winter of caused unusual (but predictable) weather in parts of the U.S.—flooding in the Southeast, an ice storm in the Northeast, and flooding in California.
Scientists cannot say with certainty that global warming is affecting El Niño or La Niña events. But a recent study by scientists suggests that global warming may be worsening the effects of El Niño. El Niño events have become more frequent with greater climate impacts over the past century.

2. Climate vs. weather
“Climate is what we Expect, Weather is what we Get”
Weather: Daily impacts of individual storms
Climate: Longer-term general conditions (The “sum” of weather)

3. El Niño & La Niña
El Niño and La Niña are changes in ocean temperatures along the equator, near Peru
Warmer than usual ocean temperatures indicate El Niño, whereas colder indicates La Niña
It occurs every 2-5 years or so. Scientists are getting better at predicting it
Where El Niño happens: If there are warm ocean temperatures in the oval it is El Niño. If the waters are cold, it’s La Niña.
Past El Niño winters since 1950:
, 63-64, 65-66, 68-70, 72-73, 82-83, 86-87, 90-95, 97-98
Past La Niña winters since 1950:
, 54-57, 64-65, 70-72, 73-76, 83-85, 88-89, 95-96, 98-99, 99-00
El Niño events have been happening for several thousand years and are a natural part of the earth’s system. However, for many years, El Niño was not well understood or monitored. Now, with satellites, buoys, and high power computer simulations of the atmosphere and ocean, we are able to make predictions of El Niño that could not have been made 10 to 15 years ago.

6. Typical US winter patterns during
El Niño & La Niña
Typical US winter patterns during
El Niño and La Niña
El Niño (warm) and La Niña (cold) are changes in ocean temperatures along Equator, near Peru.
It occurs every 2-5 years or so. Scientists are getting better at predicting it (forecasts 6 months in advance are good)
It is one of the major influences on year-to-year climate variability in the Southwest

7. El Niño conditions

9. Sea Level Pressure

12. El Niño & Arizona winter precipitation
El Niño winters
may be very wet.
Very wet winters are typically El Niño winters, but not always.
La Niña winters are typically dry &
almost never wet.
Oct-Mar Precipitation
2002
1998/99
1997/98