A car sits amid floodwater in Brandon, Florida, amid Hurricane Milton on October 9, 2024. A just-issued stocktake on the state of the world's climate noted a slew of extreme weather events last year. Photo / AFP
A car sits amid floodwater in Brandon, Florida, amid Hurricane Milton on October 9, 2024. A just-issued stocktake on the state of the world's climate noted a slew of extreme weather events last year. Photo / AFP
Our planet just experienced its warmest year – but also its first above the symbolic global warming threshold of 1.5C.
That’s among a catalogue of worrying observations in the World Meteorological Organisation’s (WHO) just-issued State of the Global Climate report for 2024.
Jamie Morton picks out three figures that tell the bleak story of another year under climate heating – and a trend that risks pushing the Paris Agreement’s goals out of reach.
1.55C
One figure we’ve often heard climate scientists and advocates cite is 1.5C.
That’s the global mean near-surface temperature mark, above the pre-industrial average, at which the world aspires to limit climate heating.
Beyond this threshold lies more heatwaves and disastrous floods.
Holding that line might still be technically possible, but it’s looking increasingly unlikely, given current trends in global warming and the human-sourced emissions driving it.
The World Health Organization (WHO) noted 2024’s mean temperature came in at about 1.55C above the 1850-1900 average, making for the planet’s hottest year in the 175-year observational record.
While that level wasn’t quite yet our globe’s “new normal” – long-term warming is presently tracking at between 1.34C and 1.41C above the pre-industrial average – scientists say it should be loudly ringing alarm bells.
As World Meteorological Organization (WMO) secretary-general Celeste Saulo put it: “It is a wake-up call that we are increasing the risks to our lives, economies and to the planet”.
The #StateOfClimate report, released today, reveals key climate change indicators again reached record levels in 2024.
— World Meteorological Organization (@WMO) March 18, 2025
Rising emissions weren’t the only factor behind 2024’s record global warmth: the report also cited changes in the solar cycle, a massive eruption, a drop in cooling aerosols and a shift to El Niño (a climate driver that in turn led to a comparatively cooler year for New Zealand).
But the greenhouse gases humanity has pumped into the atmosphere – today at their highest levels in some 800,000 years – remained the greatest climate-warmer.
The report noted a slew of extreme weather events that destroyed homes and livelihoods and pushed annual displacements to the highest levels seen since 2008.
All of that compounded the effect of shocks ranging from conflict, to drought, to high domestic food prices – yet Victoria University climate scientist Professor James Renwick worried this global reality still wasn’t hitting home for the average person.
“Greenhouse gas emissions that drive climate change just keep increasing, regardless of the bad news,” he said.
“This latest report is saying global temperatures are higher than they have been for at least 175 years – and yet 2024 will be one of the coldest years this century, as we keep adding warming gases to the atmosphere.”
In 2024, global mean sea level was the highest since the start of the satellite record, having risen from 2.1mm per year from 1993-2002 to 4.7mm per year over 2015-2024.
Along with that climbing sea level – posing a clear threat to tens of billions of dollars of property and infrastructure in Aotearoa – the report noted rising ocean heat.
About 90% of the energy trapped by greenhouse gases in the Earth system is stored in the ocean, which in 2024 reached its highest heat content in 65 years of observations.
Each of the past eight years has set a new record and the rate of ocean warming over 2005 to 2024 is more than twice that recorded between 1960 and 2005.
Ocean acidification will have implications for New Zealand's species-rich marine environment. Photo / File
Climate projections show that ocean warming – leading to more tropical storms, degraded marine ecosystems and higher seas - would continue for at least the rest of the 21st century, even for low carbon emission scenarios.
The ocean surface is also becoming more acidic, with notable decreases in pH levels observed in the Southern Ocean below New Zealand, but also the eastern equatorial and northern tropical Pacific, and some regions of the Atlantic Ocean.
Already, these irreversible changes have hit coral reefs and fisheries.
Associate Professor Melissa Bowen, of the University of Auckland’s School of Environment, said humanity now needed to prepare for the impacts of a warming ocean.
She added that it wasn’t soaking up the extra heat uniformly.
“Some places in the ocean, such as the region around New Zealand, are picking up more heat and storing it at different depths,” she said.
“How the ocean circulates determines where the heat goes - how fast it will return to the surface, how much it will change the sea surface temperature - and how it will affect the atmosphere.”
4.28 million km2
In New Zealand, one of climate change’s clearest calling cards has been the gradual loss of our postcard glaciers.
Scientists recently estimated that, since just the turn of the century, they’d lost nearly a third of their ice.
The WHO report put that grim trend in a global context, finding that 2022-24 represented the world’s most negative three-year period for glacier mass balance on record.
“This is concerning because glacier melt impacts global sea level rise, water resources, hazards, ecosystems, and cultural connection to place,” Victoria University glaciologist Dr Lauren Vargo said.
If warming eventually reached 5C, Vargo said we stood to lose almost all of the glaciers that exist today; but if it could be limited to 2C of temperature rise, then many of those in the Southern Alps might survive.
The report also set out alarming trends in the extent of sea ice at both ends of the planet.
The minimum daily extent of sea-ice in the Arctic in 2024 was 4.28 million km2 - the seventh lowest extent in the 46-year satellite record.
New Zealand's glaciers have lost nearly a third of their ice since the turn of the century. Photo / Niwa
In Antarctica, the minimum daily extent tied for the second lowest minimum in the satellite era - and marked the third consecutive year that minimum Antarctic sea-ice extent dropped below two million km2.
Renwick said that, for many years, the extent of Antarctica sea ice in the Southern Ocean had been a “hold-out” amid global trends all pointing to a warming world.
“The warming of the oceans has finally started to materialise over the surface of the southern oceans and sea ice is paying the price.
“There will be plenty of ups and downs over coming years - but the trend will very likely be down from here.”
Professor Nick Golledge, of Victoria University’s Antarctic Research Centre, said the report ultimately painted a bleak - but by now unsurprising - picture of the state of the climate.
But the most concerning aspect was that simply stabilising our emissions wouldn’t be enough to limit temperature rise to 1.5C - or even the Paris Agreement’s “safe” limit of 2C.
“Stringent mitigation is now critically important if we are to retain a habitable climate for our planet.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
