La Nina climate cycle is over: UN
La Nina is a large-scale cooling of surface temperatures that occurs every two to seven years in the central and eastern equatorial Pacific Ocean.
The effect has far-reaching effects on weather around the world, usually in the opposite direction of the El Nino phenomenon, which causes global temperatures to rise.
The temporary global cooling effects of La Nina, however, were insufficient to prevent 2020 from becoming one of the three hottest years on record.
"All naturally-occurring climate events now take place in the context of human-induced climate change, which is increasing global temperatures, exacerbating extreme weather and impacting seasonal rainfall patterns," said the WMO.
According to atmospheric and oceanic indicators, La Nina conditions have been present since August-September 2020.
As a moderate-strength event, the phenomenon appeared to have peaked in October-November.
The WMO stated that La Nina "ended in May" and that neutral conditions (i.e., neither El Nino nor La Nina) are expected to dominate the tropical Pacific in the coming months.
According to the WMO, there is a 78 percent chance of neutral conditions in the tropical Pacific until July, then a 55 percent chance from August to October.
'False sense of security'
Air temperatures over land are expected to be warmer than average from June to August "over almost the entire northern hemisphere," according to the WMO.
The end of La Nina and widespread above-average sea-surface temperatures caused by global warming are to blame.
"La Nina has a temporary global cooling effect, which is typically strongest in the second year of the event. This means that 2021 has got off to a relatively cool start -- by recent standards," said WMO Secretary-General Petteri Taalas.
"This should not lull us into a false sense of security that there is a pause in climate change."
The Mauna Loa Observatory in Hawaii is used to measure carbon dioxide levels as a benchmark reference station.
April's monthly average was 419.5 parts per million, up from 416.45 parts per million in April 2020.
"Carbon dioxide concentrations remain at record high levels and so will continue to drive global warming," said Taalas.
"There is a 90 percent likelihood of at least one year between 2021-2025 becoming the warmest on record.
"This would dislodge 2016 -- a strong El Nino year -- from the top ranking."
A busy hurricane season is on the way
The annual Atlantic hurricane season begins on June 1 and lasts until November 30.
Last year's Atlantic hurricane season set a new record with 30 named storms, including 13 hurricanes and six major hurricanes.
Given the absence of El Nino, which tends to suppress hurricane activity, another above-normal season is expected this year, according to WMO spokeswoman Clare Nullis.
The National Oceanic and Atmospheric Administration in the United States predicts 13-20 named storms this year, with six to ten of them potentially becoming hurricanes. As many as five of these storms have the potential to become major hurricanes.
At least 400 people were killed and $41 billion was lost due to the Atlantic storms of 2020.