The Weather Corner: How climate change impacts La Niña, and what it means for agriculture

We’re bringing you exclusive content from our newsletter, The Forecast, right here on Medium. Sign up for our newsletter here. This story is from our feature called the Weather Corner, where we take a deep dive into weird weather around the world, from our December 11th, 2020, newsletter.

Typical late fall through early spring upper level jet stream positions with La Niña (left) and El Niño (right) events.

This week, we’re taking a deep dive into one of the most interesting and significant weather phenomena in the world, which is coincidentally occurring with strength, as we speak: La Niña.

La Niña, the counterpart of El Niño, is characterized by lower-than-usual ocean surface temperatures in the Pacific near the Equator. It’s the result of shifting wind patterns in the atmosphere, where the jet stream curves and shifts north, and it happens every 3–5 years.

La Niña often means a cold and stormier winter across the North, while the southern hemisphere stays warmer and drier than normal. La Niña also typically results in more rain than average through Indonesia, cooler and wetter weather in southern Africa, and drier weather in southeastern China, among other impacts. In the US, La Niña events often bring drier-than-average winter conditions to the Southwest, but can cause more severe storms in the Northern part of the country due to the change in the jetstream.

It also could have had a hand in this past record-breaking Atlantic hurricane season, which we wrote about in the last two newsletters. La Niña weakens winds between the ocean surface and the upper levels of the atmosphere, which can allow hurricanes to more easily grow.

La Niña has begun to strengthen this year. A strong La Niña — defined as sea surface temperatures at least 1.5 degrees Celsius colder than average — would be the first in a decade. Strong La Niña events have different impacts on local weather conditions around the world including, for example, strong catastrophic floods in northern Australia. The 2010 La Niña event correlates with one of the worst floods in the history of Queensland, Australia.

Source: Climate.gov

Climate change has altered some of the typical impacts of La Niña.

“La Niña tends to pull down global temperatures, but in recent years we have been warming the planet so fast, it’s like hitting a small speed bump at 80 mph — it barely even registers,” CNN meteorologist Brandon Miller said in July.

It can affect agriculture, too. La Niña conditions began in September, just as corn and soybeans were being planted in South America, and wheat was going in the ground in the U.S.

Dan Basse of AgResource predicts a strong impact on the corn crop in South America. That’s due in large part to the dryness in the Southern hemisphere, which could reduce the yields of Argentine and Brazilian corn.

On the other side of the world, excess rainfall in Oceania could hinder yields and the ability to harvest palm oil.

Have any more questions about global weather events, their impact, and how they’re linked to climate change? Send them to media@climate.ai — we will choose one to answer in the next newsletter.

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