Global heating is accelerating faster than is currently understood and will result in a key temperature threshold being breached as soon as this decade, according to research led by James Hansen, the US scientist who first alerted the world to the greenhouse effect.
The Earth’s climate is more sensitive to human-caused changes than scientists have realized until now, meaning that a “dangerous” burst of heating will be unleashed that will push the world to be 1.5C hotter than it was, on average, in pre-industrial times within the 2020s and 2C hotter by 2050, the paper published on Thursday predicts.
This alarming speed-up of global heating, which would mean the world breaches the internationally agreed 1.5C threshold set out in the Paris climate agreement far sooner than expected, risks a world “less tolerable to humanity, with greater climate extremes”, according to the study led by Hansen, the former Nasa scientist who issued a foundational warning about climate change to the US Congress back in the 1980s.
Hansen said there was a huge amount of global heating “in the pipeline” because of the continued burning of fossil fuels and Earth being “very sensitive” to the impacts of this – far more sensitive than the best estimates laid out by the UN’s Intergovernmental Panel on Climate Change (IPCC).
“We would be damned fools and bad scientists if we didn’t expect an acceleration of global warming,” Hansen said. “We are beginning to suffer the effect of our Faustian bargain. That is why the rate of global warming is accelerating.”
The question of whether the rate of global heating is accelerating has been keenly debated among scientists this year amid months of record-breaking temperatures.
Hansen points to an imbalance between the energy coming in from the sun versus outgoing energy from the Earth that has “notably increased”, almost doubling over the past decade. This ramp-up, he cautioned, could result in disastrous sea level rise for the world’s coastal cities.
The new research, comprising peer-reviewed work of Hansen and more than a dozen other scientists, argues that this imbalance, the Earth’s greater climate sensitivity and a reduction in pollution from shipping, which has cut the amount of airborne sulphur particles that reflect incoming sunlight, are causing an escalation in global heating.
“We are in the early phase of a climate emergency,” the paper warns. “Such acceleration is dangerous in a climate system that is already far out of equilibrium. Reversing the trend is essential – we must cool the planet – for the sake of preserving shorelines and saving the world’s coastal cities.”
To deal with this crisis, Hansen and his colleagues advocate for a global carbon tax as well as, more controversially, efforts to intentionally spray sulphur into the atmosphere in order to deflect heat away from the planet and artificially lower the world’s temperature.
So-called “solar geoengineering” has been widely criticized for threatening potential knock-on harm to the environment, as well as over the risks of a whiplash heating effect should the injections of sulphur cease, but is backed by a minority of scientists who warn that the world is running out of time and options to avoid catastrophic temperature growth.
Hansen said that while cutting emissions should be the highest priority, “thanks to the slowness in developing adequate carbon-free energies and failure to put a price on carbon emissions, it is now unlikely that we can get there – a bright future for young people – from here without temporary help from solar radiation management”.
This year is almost certain to be the hottest ever reliably recorded, with temperatures in September described as “gobsmackingly bananas” by one climate researcher. A report this week found that the carbon budget to limit the world to 1.5C of heating is now nearly exhausted due to the continued burning of fossil fuels and deforestation.
But while scientists are clear about this being part of an upward trend of global heating, there is as yet no agreement that this trend is accelerating.
Michael Mann, a climate scientist at the University of Pennsylvania, said that Hansen and his co-authors are “very much out of the mainstream” in identifying an acceleration in surface heating that has “continued at a remarkably constant rate for the past few decades”. Mann said that cuts to shipping emissions have only a tiny effect on the climate system and that calls for solar geoengineering are misguided and a “very slippery slope”.
Bärbel Hönisch, a paleoclimatologist at Columbia University, said she had “some reservations” about the certainties expressed in Hansen’s research about the state of the Earth’s climate millions of years ago, which helps predict the consequences of warming today. “I’d be a little more reserved, but they may well be correct – it’s a nicely written paper,” she said. “It raises a lot of questions that will trigger a lot of research that will bring our understanding forward.”
Some other researchers are less skeptical of Hansen’s dire warning of supercharged global heating, highlighting his previous prescient warnings about the climate crisis that have largely played out due to decades of inaction to stem the use of fossil fuels.
“I think [Hansen’s] contention that the IPCC has underestimated climate sensitivity somewhat will prove to be correct,” said Rob Jackson, a Stanford University scientist and chair of the Global Carbon Project. “It’s hard to know what’s unlikely any more in terms of warming. No fossil fuel has declined in use yet globally, not even coal.
“I think Hansen’s pessimism is warranted. He stood up 35 years ago and sounded the alarm – and the world mostly ignored him, and all of us.”
