Hot, hot, hot. April was the seventh month in a row to smash global temperature records, but a brief respite could be on the horizon.
Since October, every month has exceeded the 1951-1980 monthly global temperature average by more than 1 °C.
The ongoing heat wave is being fuelled by a double whammy – background global warming and a strong El Niño cycle.
The relative contributions of these two phenomena are difficult to gauge, but clues can be found in previous El Niño cycles, says Blair Trewin of the Australian Bureau of Meteorology.
“If you compare the temperatures of the last 12 months with the same stages of the last strong El Niño event in 1997 and 1998, it’s about 0.3 °C warmer this time round,” he says. “This is consistent with an overall warming trend.”
However, the record run may be interrupted when La Niña, the opposite weather cycle to El Niño, kicks in towards the end of the year, he says.
El Niño is a cyclical weather pattern that warms the central and eastern tropical Pacific Ocean, while La Niña has the opposite cooling effect.
The US government’s National Oceanic and Atmospheric Administration (NOAA) reported last week that the current El Niño phase, which began in 2015, has a 75 per cent chance of switching to La Niña as early as September.
This transition is likely to reduce sea surface temperatures in the central tropical Pacific to between -0.5 °C and 0.5 °C from average, from a high of more than 2 °C above average when El Niño peaked in November, according to the World Meteorological Organisation.
Average global temperatures are likely to fall slightly as a result, Trewin says. “A strong La Niña like we saw in 2010 and 2011 will drop global temperatures by 0.1 to 0.2 of a degree, but weaker events won’t have as strong an impact,” he says.
Even if La Niña does put the brakes on global temperature, the effect is likely to be short-lived, says Agus Santoso of the University of New South Wales, Australia.
“La Niña sometimes lasts for a year, sometimes two years,” he says. “It will be very interesting to see what happens when La Niña emerges. If records are still being broken, it will suggest that it is background warming that is playing the key role.”