Forecast centres around the world have now declared that an El Niño, the most powerful fluctuation in our climate system, has begun in the tropical Pacific.
For more than a year, scientists have been talking of an increased risk of the start of El Niño conditions in the tropical Pacific.
Scientists have been watching closely because it can change the odds of floods, droughts, heat waves and cold seasons for different regions around the world and can even raise global temperatures.
Early signs of an El Niño last year failed to fully develop and atmospheric conditions remained close to neutral into the start of 2015.
Now, however, observations from the tropical Pacific show that we have moved to weak El Niño conditions for the first time in five years.
While it is still too early to determine with confidence how strong this El Niño might be forecast models from centres around the world – including the Met Office – suggest this El Nino could strengthen from September onwards.
What are the impacts likely to be?
El Niño is a warming of the Pacific Ocean as part of a complex cycle linking atmosphere and ocean. It sees a huge release of heat from the Pacific Ocean into the atmosphere, which can disrupt weather patterns around the world.
It can be linked with poor monsoons in Southeast Asia, droughts in southern Australia, the Philippines and Ecuador, blizzards in the United States, heatwaves in Brazil and extreme flooding in Mexico.
The consequences of El Nino are much less clear for Europe and the UK.
Each El Nino event is unique, however, so it’s not possible to say exactly what the consequences will be for any given year.
What will happen next?
Predicting exactly how an El Niño might develop remains difficult, but as we move a few months ahead it’s likely forecast models will provide a higher level of certainty about what will happen.
The current outlook suggests that at least a moderate El Nino is likely and there is a risk of a substantial event.
What does this mean for the UK?
There has been some media speculation about how the El Niño conditions could impact our weather over the coming months.
However, even a strong El Niño only slightly changes the risk of extreme UK spring and summer weather and we wouldn’t expect it to be the dominant driver of our weather over the next few months.
Looking further ahead, there are a number of factors that affect winter conditions in Britain. The increase in risk of a colder winter this year from the developing El Niño is currently considered small.