One of modern climate science鈥檚 pioneers is warning that the world isn鈥檛 just steadily warming but is dangerously accelerating, according to a study that some other scientists call a bit overheated.
The work from former NASA top scientist James Hansen, who since leaving the space agency has become a prominent protester against the use of fossil fuels, which cause climate change, illustrates a recently surfaced division among scientists about whether global warming has kicked into a new and even more dangerous gear.
Hansen, to the harms of climate change in , said Thursday that since 2010, the rate of warming has jumped by 50%. Hansen argues that since 2010 there is more sun energy in the atmosphere, and less of the particles that can reflect it back into space thanks to efforts to cut pollution. The loss of those particles means there鈥檚 less of the cooling effect that they can have.
Hansen said a key calculation used in figuring out how much the world will warm in response to carbon pollution shows much faster warming than the United Nations鈥 Intergovernmental Panel on Climate Change estimates. He called the international goal of limiting warming to Celsius (2.7 degrees Fahrenheit) since pre-industrial times 鈥渄eader than a doornail鈥 and said a less stringent goal of 2 degrees Celsius (3.6 degrees Fahrenheit) is on its deathbed. That matters because increases in average global temperatures lead to more frequent and intense extreme weather events.
鈥淭he next few years will show that we indeed do have an acceleration in the global warming rate,鈥 Hansen said in a press briefing. 鈥淎nd it鈥檚 based on simple good physics.鈥
鈥淭he planet is now out of (energy) balance by an incredible amount, more than it ever has been,鈥 said Hansen, who has been nicknamed the Godfather of Global Warming.
Several climate scientists contacted by The Associated Press expressed skepticism about Hansen's study, tinged with respect for his long-term work.
Hansen鈥檚 study in Thursday鈥檚 journal is broad-ranging 鈥渂ut has little by way of analytical depth or consistency checks when making claims quite far outside the norm,鈥 said Robin Lamboll, a climate scientist at the Imperial College of London. 鈥淚t seems primarily aimed at convincing policymakers rather than scientists.鈥
University of Pennsylvania climate scientist Michael Mann, who insisted that since 1990 warming is steadily increasing but not accelerated, to Hansen鈥檚 claims and said climate change right now is bad enough and there鈥檚 no need to overstate the case. Mann said 鈥渋t has always been risky to ignore (Hansen鈥檚) warnings and admonitions鈥 but when claims are made so out of the mainstream the standard for evidence is high, and he said Hansen hasn鈥檛 met them.
Yet a check of lends support to Hansen's modeling.
Hansen鈥檚 study said from 1970 to 2010, the world warmed at a rate of 0.18 degrees Celsius per decade, but projected that would increase to a rate of at least 0.27 degrees Celsius per decade after 2010. NOAA data shows that 0.27 degrees is the rate since September 2010.
That starting date is key because that's when scientists could start to see the effect of clean air regulations that reduced aerosol pollution and the amount of sulfur in fuel used by ocean shipping, Hansen said. That type of more traditional sooty air pollution has a cooling effect that masks a fraction of the warming from the burning of coal, oil and natural gas, Hansen and many other scientists said.
When scientists try to figure out future and past warming one of the crucial variables is climate sensitivity, which is how much the world warms when carbon dioxide levels in the air double. These calculations have had a wide range and scientists have yet to settle on it, but the latest U.N. climate panel said it is within a , with the likely range between 2.5 and 4 degrees and 3 degrees being a good midpoint.
Hansen鈥檚 study has it at 4.8 degrees Celsius. That鈥檚 within the widest range, but barely.
It鈥檚 that high because past research was based on wrong calculations of how fast the world warmed between glacial periods, Hansen said.
Past calculations were based on plant and animal fossil data, figuring microbiotic organisms wouldn鈥檛 adapt to warming, but would move to their preferred temperature range. Hansen said recent research shows that the organisms adapt and stay put, and when his team calculated past temperature changes based on chemical, not biological markers, it showed much faster warming for when carbon dioxide doubled in Earth鈥檚 ancient history.
Studies on climate sensitivity vary widely and are inconsistent, with showing 2.8 degrees not 4.8, said climate scientist Zeke Hausfather of Berkeley Earth and the tech company Stripe. He said Hansen鈥檚 calculations are 鈥渘ot implausible but not particularly well supported by the literature.鈥
Stanford University climate scientist Rob Jackson, however, said 鈥淚 tend to trust Hansen, despite his advocacy. I think his contention that the IPCC has underestimated climate sensitivity will prove out.鈥
Hansen said a more recent climate model 鈥 downplayed by the U.N. climate panel for running too hot 鈥 is actually more accurate than the ones mainstream climate scientists prefer based on cloud conditions in the southern ocean.
With a strong natural El Nino, which tends to temporarily warm the globe, and and in the , scientists in the past month about what鈥檚 happening to the globe.
Mann said the warming the world is seeing is what has long been predicted and is not the indication of something unusual or acceleration. The increases reported, he said, are statistically insignificant.
Hausfather said the world is warming faster, but he calculated the rate at 0.24 degrees Celsius per decade instead of Hansen's 0.27 degrees.
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