La Niña

If you blow hard across the top of a mug of hot cocoa, the warm surface liquid glides to the far side, and the cooler drink underneath wells up to take its place. The exact same thing happens in the tropical Pacific Ocean. There, powerful atmospheric currents known as trade winds blow steadily from east to west.

Normally, these winds carry warm surface water toward Southeast Asia. But during a La Niña, the trade winds kick into overdrive. They aggressively shove warm water westward, allowing cold water from deep below (dozens to hundreds of meters down) to surge upward and replace it. This process is called upwelling, where deep cold water rises to the surface.

As this deep, chilly water spreads across the surface, ocean temperatures off the coast of Peru plunge. Even a seemingly minor drop of 0.5°C to 2°C is enough to throw the entire global atmosphere off balance.

Whenever ocean temperatures change, the atmosphere resting above them transforms as well. In the western Pacific (around Indonesia, the Philippines, and Australia), warm water piles up deep, making the sea unusually warm. Warm air rises rapidly, creating towering thunderclouds that bring frequent downpours and severe flooding. Tropical cyclones also become more common near Australia, and typhoons tend to form closer to the Asian mainland.

Meanwhile, the eastern Pacific tells the opposite story. Over cold water, air cools and sinks rather than rising, preventing clouds from forming. Over North America, the winter jet stream shifts farther north, leaving the southern United States unusually dry. This prolonged lack of rain triggers severe droughts and heightens the risk of dangerous wildfires.

Because the ocean and atmosphere are locked in a continuous loop, a small temperature shift in the equatorial Pacific triggers a massive worldwide domino effect.

In Spanish, La Niña means 'the little girl'—named as the counterpart to El Niño, 'the little boy' (referencing the Christ child). While El Niño happens when trade winds weaken and ocean waters warm up, La Niña is the opposite extreme, marked by supercharged winds and unusually cold seas.

If El Niño acts like an oversized space heater for the planet, La Niña serves as an oceanic air conditioner, briefly slowing global temperature rise. During extended La Niña periods, the upward climb of Earth's average surface temperature often appears to hit a temporary plateau.

However, this does not mean global warming has stopped. Excess thermal energy continues to accumulate deep in the oceans, while extreme weather simply shifts into different gear. For example, East Asia often experiences harsher, colder winters as the Siberian High strengthens, though other atmospheric patterns can alter the outcome year by year.