La Niña Alert: Weather Extremes Are On the Way

By Michael D. Lemonick

The overall long-term trend in Earth’s climate is toward higher temperatures, as humans continue to pump carbon dioxide and other heat-trapping greenhouse gases into the atmosphere. The temperature rise is evident on a scale of decades, but over shorter time periods, natural climate variations can accelerate or hold back the warming in different parts of the world — and one such variation is likely to dominate weather in the U.S. this coming winter.

Map of projected winter precipitation anomalies in the U.S. Credit: NOAA.

It’s La Niña, a periodic cooling of water in the equatorial Pacific that happens about every two to five years. As you can see in this Climate Center video, La Niña's cooling effect could keep this year — the warmest on record globally so far — from holding onto that title.

It could also lead to a winter of weather extremes that differ from those seen last year. According to a new report issued yesterday by the National Oceanic and Atmospheric Administration (NOAA), much of the Pacific coast, the northern parts of North Dakota and Montana, and central Alaska are likely to be cooler and wetter than average, while the South and Southeast are likely to be warmer and drier. This may have major implications for drought conditions, which have emerged in the Southeast and persisted in parts of the Southwest. Historically, La Niña events have been associated with noteworthy droughts in the Southwest.

Map of projected winter temperature anomalies in the U.S. Credit: NOAA.

La Niña is essentially the mirror image of El Niño, which is characterized by warming in the Pacific — but it turns out that either one can disrupt weather patterns, just in different ways. Currently the 2010 La Niña is classified as moderate to strong in strength, as judged by how cold the ocean temperatures are compared to average. This means that La Niña is more likely to be the main influence on the average weather pattern this coming winter, although other variables will also enter into the picture.  Here’s how NOAA put it on its website:

A moderate to strong La Niña will be the dominant climate factor influencing weather across most of the U.S. this winter.

None of this comes as a big surprise to climate scientists, who have been tracking alternating El Niño/La Niña events for years; and Climate Central reported weeks ago that “you’re going to be hearing a lot more about La Niña in coming months.”