The tropical Pacific Ocean entered La Nina state in October 2025, according to the Beijing Climate Centre.

La Nina refers to a sustained cooling of sea surface temperatures across large areas of the eastern and central equatorial Pacific. The development has raised public concern about whether this winter will be warmer or colder than usual and about the likelihood of low-temperature events, including rain, snow, and freezing conditions.

Climate experts explain that meteorological agencies track the sea surface temperatures in the central-eastern equatorial Pacific using the Nino 3.4 index. When the index drops below minus 0.5 degrees Celsius, the region is considered to be in a La Nina state.

However, a La Nina state is not the same as a La Nina event. According to national standards, a La Nina event is officially recognized only when the Nino 3.4 index stays below minus 0.5 degrees Celsius for at least five consecutive months.

Experts from the Zhejiang Provincial Climate Center note that La Nina usually occurs every two to seven years. However, in recent years, its frequency has increased, a trend closely linked to the complex mechanisms of global warming.

Earlier this year, a weak La Nina event had already taken place, which allowed cold subsurface waters in the central-eastern equatorial Pacific to keep accumulating and created favorable conditions for La Nina to re-emerge toward the end of the year.

This has raised questions about the possibility of a so-called "double La Nina" this winter. Experts clarify that a "double La Nina" does not mean two events within the same year, but rather La Nina events occurring during two consecutive winters.

According to forecasts from the National Climate Center, the likelihood of a double La Nina event happening this winter is still low.