As humans put more and more heat-trapping gases into the atmosphere, the Earth warms. And the warming is causing changes that might surprise us. Not only is the warming causing long-term trends in heat, sea level rise, ice loss, etc.; it’s also making our weather more variable. It’s making otherwise natural cycles of weather more powerful.
Perhaps the most important natural fluctuation in the Earth’s climate is the El Niño process. El Niño refers to a short-term period of warm ocean surface temperatures in the tropical Pacific, basically stretching from South America towards Australia. When an El Niño happens, that region is warmer than usual. If the counterpart La Niña occurs, the region is colder than usual. Often times, neither an El Niño or La Niña is present and the waters are a normal temperature. This would be called a “neutral” state.
The ocean waters switch back and forth between El Niño and La Niña every few years. Not regularly, like a pendulum, but there is a pattern of oscillation. And regardless of which part of the cycle we are in (El Niño or La Niña), there are consequences for weather around the world. For instance, during an El Niño, we typically see cooler and wetter weather in the southern United States while it is hotter and drier in South America and Australia.