Meteorologist explains how climate change will affect the back-and-forth La Niña, El Niño weather patterns

This is a simple question that may not be so easy to answer.

Scientists expect rising global temperatures to affect weather patterns known as La Nina and El Niño — but how strong that effect will be is unclear. will depend on many other variables that contribute to our daily weather and long-term climate.

These factors include natural variability, competing weather patterns, location, geography, and even ocean chemistry.

What are El Nino and La Nina anyway?

Before we dive into the nitty-gritty, let’s start with the basics.

During El Niño years, warm waters from the Pacific near the equator push warm, tropical air into our region. This pattern is most prominent in the winter months and usually means warmer, drier weather.

We are currently in an El Nino year, so you may be seeing some of these effects. Mountain snowpack is down across the board (although there are other factors as well). Seattle had its warmest December on record, followed by another record-setting warm week in January.

The pattern is ending now, though, and meteorologists expect La Niña to replace it.

Think of La Nina as the mirror image of El Niño. Cooler ocean water in the tropics pushes cooler air into the Pacific Northwest. Again, most prominent in the winter months, this usually makes for cold and wet weather.

Of course, these patterns affect each region of the continent differently, said Dennis Hartman, professor of environmental sciences at the University of Washington.

For example, La Ninas mean more storms and hurricanes for the southeastern United States and drought for the southwest. The effects in the Pacific Northwest are relatively minor, Hartman said.

“It’s not like off the coast of South America, where an El Niño shuts down the fishery,” Hartman said.

How does climate change factor in?

Simply put, climate change – caused by human burning Biofuels– is warming the atmosphere. So it’s likely to moderate the warming effects of El Nino and reduce the cooling caused by La Nina, said Aaron Levine, a UW research scientist who has a doctorate in meteorology.

For example, next January’s average temperature in the Pacific Northwest could be one degree warmer than normal due to climate change, Leon said. If El Nino conditions also prevail this year, we can expect temperatures to rise by half a degree from this pattern.

Those two effects will combine for a January that is 1.5 degrees above normal, Levin said.

For the record this is a simplified version. These things don’t happen in a vacuum and never work so cleanly.

Consider the same scenario at the other end of the spectrum.

If climate change raises the average temperature for January by one degree above normal and La Nina lowers temperatures by half a degree, we’ll see a month that’s only half a degree above average.

There is still a warmer trend due to climate change, but a La Nina year will moderate this trend, if only for a few months.

“On an individual level, you probably won’t notice this change all at once,” Levin said. These patterns—and their trends—are measured on decades, not on daily or even annual scales.

Nick Bond, a state climatologist with the UW, said there’s also a bigger picture of whether climate change will increase the frequency or intensity of El Niño and La Niña patterns. But the data is still unclear.

“Like many other things related to climate change, we’re still learning,” Bond said. But these are some of the questions climate scientists are asking, and they are actively seeking answers.

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