La Niña is now present in the tropical Pacific and forecasters are suggesting these conditions will continue throughout the winter months.
La Niña is one of the three phases of the phenomenon known as the El Niño-Southern Oscillation, El Niño – the warm phase, La Niña – the cool phase and lastly the neutral phase. During La Niña strong trade winds blow warm water towards the west Pacific causing an upwelling of cool water from the ocean depths in the east Pacific leading to variations in global weather.
These changes in the location of warm and cool ocean water lead to a shift in rainfall towards the western Pacific putting areas such as north-east Australia, and Indonesia at risk of heavier than normal rainfall. While areas on the other side of the tropical Pacific, such as California, could be at risk of drought. La Niña can even influence the Atlantic jet stream and our weather here in the UK.
“In late autumn and early winter it historically promotes high pressure in the mid-Atlantic, which stops Atlantic weather systems from delivering mild air to the UK, and therefore can allow cold conditions to intensify. However, in late winter La Niña can drive a shift of the jet stream towards the Poles increasing storminess and heavy rainfall, while bringing milder conditions”.
Other factors affecting our winter weather.
The Quasi-Biennial oscillation, the variation in winds high above the equator, is in its westerly phase at present and this increases the chance of a mild, wet and stormy winter.
Meanwhile, the sun is in a new solar weather cycle, solar cycle 25. This cycle started around 9 months ago and at this stage can be associated with colder winter weather.
How will La Niña impact global temperatures?
Globally 2020 remains on track to be one of the warmest on record. Although La Niña historically reduces global temperatures, it is not expected to be enough to counterbalance human-induced climate change, but it may be enough to just prevent 2020 from being a new record.
This comes after 2019 was one of the three hottest years on record and all the years since 2013 have been warmer than any previous years since records began in the 1800s.