We got so tired of repeating those words every month. This week, we reached a disturbing milestone: the one year mark. We just lived through twelve record-smashingly hot months, April to April. On top of that, 2016 is now all but assured to become the hottest year on record -- stealing the title from 2015 which just became the hottest year on record.
Will the sizzling streak ever end? Our planet could see some relief by the end of the year, if El Niño is overtaken by La Niña. But the effect would only be temporary.
We're currently on the tail end of a very strong El Niño event which is partially responsible for our record run of record hot months. El Niño, which comes every three to seven years, is characterised by a warming of surface ocean waters across the equatorial Pacific, an effect that disrupts atmospheric circulation patterns around the globe. Some parts of the planet become cooler and wetter, while other regions get warmer and drier. But on the whole, El Niño releases trapped ocean heat into the atmosphere, resulting in a slight uptick in global temperatures.
La Niña brings the equatorial Pacific back down to a simmer.
"It's sort of the opposite of El Niño, which affects global circulation by pumping extra heat out of the ocean," meteorologist and Weather Underground blogger Bob Henson told Gizmodo. "La Niña draws heat back in."
While the regional effects of La Niña are every bit as complex as those of El Niño, Earth's thermostat tends to dial down a bit during La Niña years. After new temperature records were set during the 1997-1998 El Niño, a three year La Niña phase saw the planet cool slightly. Heat records were broken again during the 2009-2010 El Niño, but during the subsequent La Niña, global average temperatures fell by 0.1 to 0.2C.
Global averaged temperature anomalies as compared with historic averages, from 1880 -- present day. Image: NOAA
What will happen as our current El Niño fizzles out is not yet certain. NOAA's most recent models predict about a 75 per cent chance of La Niña developing during spring or summer -- which sounds like pretty good odds. Even if strong La Niña conditions emerge by spring, however, 2016 is still going to be a scorcher of historic proportions.
That's because the double whammy of a strong El Niño and the underlying global warming trend have resulted in a tremendous buildup of heat in the atmosphere. And that heat is going to take time to dissipate. In fact, Gavin Schmidt, head of NASA's Goddard Institute for Space Studies, estimates a greater than 99 per cent chance that 2016 will be the hottest year yet, given the incredible head start we've already had over last year.
On the other hand, the emergence of La Niña conditions could pump the brakes on planetary record-breaking in 2017.
"I think it will be difficult for 2017 to beat 2016 -- in fact it would be shocking -- if La Niña comes into play," Henson said. "We could have one or more years that don't quite match 2016, assuming this year sets the record."
It's crucial to stress that any slight global warming relief in the coming year or two will be temporary. In the long term, our planet will keep heating up as long as we're pumping carbon into the air, and there's no indication that we're going to stop any time soon. We're teetering on the edge of a world where atmospheric carbon concentrations are permanently above 400 parts per million; the highest they have been in millions of years. The rate of carbon emissions hasn't been this high any time in the past 66 million years -- since the dinosaurs went extinct or even earlier.
And Earth's thermostat is responding in a predictable way. Global average temperatures are now nearly 1.5C warmer than they were in the pre-industrial past.
"Every decade for the last half century has been warmer than the preceding one, and there's no sign that's going to change," Henson said. "El Niño is a blip of heat on top of the ever-warming planet, and La Niña chips away at that slightly."