A local attempts to extinguish a fire near the Greek mainland city of Volos. Photo: AFP / Eurokinissi / Tatiana Bolari
Humanity has experienced its first year of living at temperatures most countries have been trying to avoid - 1.5C above the preindustrial average - says the EU's climate service.
Other major temperature records also agree that the world was about 1.5C degrees hotter last year than before the boom of fossil fuels.
It's not a permanent state of affairs, and is not expected to become normal until the 2030s, but climate scientists say 2023 was "extraordinary" and a sign of what is to come.
It matters politically when the the 1.5C threshold is crossed permanently, because it is the level New Zealand and many other nations are aiming to stay within, under the Paris Agreement.
The goal was set after a landmark 2018 report laid out how much worse the damage to people, nature and property would be from 2C of heating, versus staying at 1.5C.
But climate scientist Nathanael Melia of Climate Prescience says the physical reality is there is no magic number - every fraction of a degree hotter has an impact.
Climate extremes do not go up in a tidy line, so a small increase in average temperatures can have major effects, he says.
Tristan Meyers Photo: NIWA
Niwa forecaster Tristan Meyers explains that it is not like taking a gentle 21C degree summer's day and turning it up to 22.5C.
"What we're really measuring is the amount of energy and heat that is stuck in the atmosphere. Think about the oceans. The oceans are enormous and we're heating up the oceans and it's causing a lot of things to destabilise."
2023 brought New Zealand's second-hottest average temperatures, rounding out an unwelcome trifecta, making the past three years the country's hottest three on record.
Meyers says the hotter averages can push out extremes to levels forecasters have not seen previously. Increasingly, extremely hot and dry conditions will fall back to back with extreme rain, worsening the impacts.
Meyers said last year was exceptional, but in 10 years that heat will be normal.
"There is an up and down trend, but if you smooth it out...over decades, the trend line is up," he said.
Melia said last year's global record heat was a bounceback, after three years of heat suppression. Before that Covid kept emissions down, as did three years of a La Nina climate system, before the "spring" rebounded last year with a flip to El Nino and economies recovering, he said.
He said it was ironic that cleaning up deadly air pollution from smokestacks and vehicles also temporarily increased temperatures, because the pollutants acted as mirrors reflecting some of the sun's heat.
Melia and Meyers agreed that with an El Nino system influencing temperatures, fossil fuels' impact could help boost the globe to another record-breaking year in 2024.