We've had 12 months of recordbreaking global heat. How close are we to passing the 1.5 C limit?
While the last 12-month pe‐ riod globally reached 1.64 C above pre-industrial levels, according to the latest data from the Copernicus cli‐ mate research program, that isn't quite the same as breaching the 1.5 C limit set in the 2015 Paris Agreement.
But it's a major alarm that we're close, and that global warming has continued to speed up in the past few years.
Each month from July 2023 to June 2024 was the hottest on record for that month, and each one reached or crossed 1.5 C above that month's pre-in‐ dustrial average, the Euro‐ pean program said.
The warming is driven in part by the natural El Niño weather pattern, which typi‐ cally raises temperatures. But the underlying trend of global warming is clear and experts are pointing to fac‐ tors in addition to green‐ house gas emissions that may have pushed tempera‐ tures to the current record levels.
More than greenhouse gases to blame?
Zeke Hausfather, a scientist with Berkeley Earth, a nonprofit that works on data analysis for climate science, says the temperature rise is in line with what their climate models predict and the accel‐ eration of global warming being seen over the past 15 years.
"It is a pretty dire sign that the world will soon exceed the 1.5 C target, and that we have effectively waited too late to reduce emissions to avoid it," he said in an email.
"The recent 12-month pe‐ riod above 1.5 C is also in line with an apparent recent ac‐ celeration in the rate of warming which is in line with what our climate models ex‐ pect in a world where planetcooling aerosol emissions (e.g. of sulfur dioxide) are being rapidly reduced while emissions of CO2 and other greenhouse gases remain at record high levels."
Those aerosol emissions refer to air pollutants from things like burning coal and shipping fuel. New regula‐ tions have reduced the emis‐ sions of these pollutants which are harmful to human health, but also reflect heat and have a cooling effect on the atmosphere.
Reducing their emissions, some models are suggesting, could be having a warming effect.
The magnitude of heat in 2023 has scientists looking more seriously at the impact of removing these aerosols from the atmosphere - and the long-term impact on cli‐ mate change, according to Bill Merryfield, a climate sci‐ entist at Environment and Climate Change Canada.
"2023 was so extraordi‐ nary that there's been a lot of speculation that there may have been effects on top of the greenhouse gas driving of global warming," said Mer‐ ryfield, referring to the im‐ pact of the new fuel regula‐ tions.
"The magnitude of the ef‐ fect is still being studied and debated. Some scientists think it's very small, some think it may be significant," Merryfield said.
How is this different from the Paris threshold?
The alarming statistics fur‐ ther point to a climate sys‐ tem teetering on the edge, with the impacts of that warming being seen in cli‐ mate disasters like storms, floods and extreme heat hit‐ ting countries around the world, experts say.
But those impacts don't reflect what it actually means to cross the 1.5 C threshold of the Paris climate accord, which refers to a more longterm shift in average temper‐ atures.
"Crossing 1.5 C for 12 months is not the same as crossing the threshold year after year in a global average sense," said Stanford Univer‐ sity climate scientist Rob Jackson. "It's different for ice melt, it's different for all kinds of processes."
Jackson's upcoming book, Into the Clear Blue Sky, talks about climate solutions and the urgent need to repair the damage to the atmosphere.
"It's surprising and dis‐ couraging to be so close to crossing the 1.5 C threshold," he said. "We've sprinted right to the edge of that threshold quickly and quite cavalierly."
Beyond extreme weather, pushing global average tem‐ peratures past 1.5 C would have serious impacts on sealevel rise, and could possibly start triggering climate tip‐ ping points, such as the irre‐ versible melt of the Arctic permafrost or a change in major ocean currents that regulate global weather.
These major impacts would not be seen if only a few years temporarily crossed the 1.5 C threshold.
According to the World Meteorological Organization, 2023 was the warmest year on record, and there's an 80 per cent chance that at least one of the years between 2024 and 2028 will exceed 1.5 C.
Back in 2015, the chance of this was close to zero, ac‐ cording to the WMO.