Another La Niña impacts temperatures and precipitation – but not climate change

Geneva, November 30, 2021 (WMO) РLa Ni̱a has grown for the second year in a row and is expected to last until early 2022, influencing temperatures and rainfall. Despite the refreshing influence of this natural climatic phenomenon, temperatures in many parts of the world are expected to be above average due to accumulated heat trapped in the atmosphere due to record levels of greenhouse gases, according to the World Meteorological Organization. (OMM).

Most models indicate that the La Ni̱a 2021/2022 event is likely to be weak to moderate Рslightly weaker than the 2020/2021 event.

Even so, climate sensitive sectors like agriculture, health, water resources and disaster management will be affected. WMO is providing support and advice to international humanitarian agencies in an attempt to reduce impacts at a time when adaptive capacities in vulnerable countries have been strained by extreme weather conditions and the continuing pandemic of COVID-19.

La Niña refers to the large-scale cooling of ocean surface temperatures in the central and eastern equatorial Pacific Ocean, associated with changes in tropical atmospheric circulation, namely winds, pressure, and precipitation. It usually has the opposite effects on weather and climate like El Niño, which is the warm phase of what is called the El Niño Southern Oscillation (ENSO).

“The cooling impact of La Niña 2020/2021 – which is typically felt in the second half of the event – means 2021 will be one of the ten hottest years on record, rather than The Year the hottest. This is a short-term respite that does not reverse the long-term warming trend or reduce the urgency of climate action, ”said WMO Secretary-General Professor Petteri Taalas .

According to the WMO update, there is a high probability (90%) that tropical Pacific Sea surface temperatures will remain at La Niña levels until the end of 2021, and a moderate chance ( 70 to 80%) that they persist at La Niña levels. until the first quarter of 2022. This is based on forecasts from the WMO World Long Range Forecast Production Centers and expert interpretation.

Global seasonal climate update

The Southern Oscillation El Niño (ENSO) is the dominant driver of natural climate variability and also the main source of seasonal climate predictability. In a warmer world, the associated variability of ENSO precipitation on a regional scale is likely to intensify, according to the latest report from the Intergovernmental Panel on Climate Change (IPCC AR6 WG1).

El Niño and La Niña are not the only factors, and no two La Niña or El Niño events are the same. WMO therefore now publishes a monthly Global Seasonal Climate Update (GSCU) to provide additional actionable information to policy makers.

In addition to El Niño and La Niña, the GSCU incorporates influences from other climatic factors, such as the North Atlantic Oscillation, Indian Ocean Dipole, to assess their likely effects on regional surface temperature and precipitation regimes and, as such, used to inform much of the seasonal discussions with the United Nations and other partners.

Therefore, decision makers should always monitor the latest seasonal forecasts to get the most recent information.

Probabilistic surface air temperature forecast for December-February 2021-2022.

The reference period is 1993-2009.

The figure is generated by the WMO Main Center for the Long Range Forecasting Multi-Model Set.

Despite poor La Niña conditions in the central and eastern equatorial Pacific, significantly warmer-than-average sea surfaces elsewhere dominate the air temperature forecast for December-February 2021-2022, according to the GSCU.

Many land regions are expected to experience above average temperatures, with the only major exceptions being northwestern North America, the Indian subcontinent, the Indochinese Peninsula and Australia.

An exceptionally warm winter is expected in the far north and northeast of Asia and the Arctic. Above-average temperatures are also expected in eastern and southeastern North America, including much of the Caribbean, and in northeastern Asia and much of the Europe, depending on the model.

Further south, above-average temperatures are forecast over a large area of ​​the maritime subcontinent extending into the South Pacific, as well as near Equatorial Africa extending southeast over Madagascar.

Near normal or below normal temperatures are forecast for most of South America north of about 15º S, while much of the west coast of South America is expected to experience temperatures below normal.

Precipitation

Some typical La Niña rainfall impacts are expected. There are increased chances of abnormally dry conditions along the equator centered near the date line and extending to the southernmost part of South America and into the northwestern parts of southern Asia. and the Middle East.

Abnormally humid conditions are forecast for parts of Southeast Asia immediately north of the equator and extending into the Southwest Pacific and North Central Pacific, as well as the Northeast and the extreme northwest of South America.

There are weaker indications of abnormally humid conditions over parts of western North America and parts of southern Africa, as well as over much of Australia.

Over much of the rest of Africa, Europe and Asia, forecast precipitation is inconsistent.

Probabilistic precipitation forecast for the December – February 2021-2022 season.

The reference period is 1993-2009.

The figure is generated by the WMO Main Center for the Long Range Forecast Multi-Model Set.

The World Meteorological Organization is the authoritative voice of the United Nations system on weather, climate and water