James Hansen, the former director of the NASA Goddard Institute for Space Studies, commonly known as the Godfather of Climate Science, and three colleagues, Makiko Sato, Reto Ruedy, and Leon Simons, suggest that by early next year, the world may have reached the dreaded 1.5 Celsius above long-term temperature average. Hansen’s testimony to Congress three-plus decades ago was the first time climate change finally became an issue in international mass media.
Keeping temperature rise below the 1.5 C temperature limit was the fundamental goal of the Paris Climate Agreement. In climate circles, it “has been widely adopted as a guardrail for avoiding worsening devastation that affects lives, livelihoods and nature.” In September, news that the temperature rise had reached 1.8 caught many of us off guard.
It does not mean that the 1.5 C guardrail is gone. According to reporting by Adam Morton of The Guardian, the Intergovernmental Panel on Climate Change (IPCC) noted that 1.5 C temperature would need to be trending for twenty years to be determinative of a breach. James Hansen’s paper challenges that timeframe. They argue that the energy imbalance (more sun reaching Earth than being reflected to space) guarantees increasing temperatures.
Morton covers the technical release of Hansen’s most recent paper published at Columbia University Mailing.
For the past four months, the globe has been 0.44C hotter than in 2015, a year chosen because it was the last time we were heading into an El Niño, which tends to warm the planet. The scientists argue if this keeps up until the northern spring (the southern autumn) the 12-month average will be at least 1.6C above temperatures more than a century ago.
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They say that would mean 1.5C had been reached “for all practical purposes” and “there will be no need to ruminate for 20 years, as the IPCC proposes” about whether we have actually got there. “On the contrary, Earth’s enormous energy imbalance assures that global temperature will be rising still higher for the foreseeable future,” they say.
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Hansen and co dedicate most of their paper to what is causing the recent heat surge. They suggest the current El Niño is a relatively minor player compared to previous similar events, and may ultimately be smaller than the “super” El Niños in the hot years of 1997-98 and 2015-16.
They argue a more likely explanation for a warming spike could be a reduction in human-made aerosols, particularly from power plants and factories in China and the global shipping fleet. Aerosols interact with sunlight and clouds to produce a cooling effect that until recently has offset some of the underlying heat caused by greenhouse gases in the atmosphere. A decline in aerosols pollution, motivated by a desire to improve air quality, could unmask human-induced heating already in the global system.
Hansen has long described this as the Faustian climate bargain. Using fossil fuels releases both aerosols and greenhouse gases, but the cooling effect of the former lasts only days, while the warming of the latter lasts centuries. He says eventually the payment – a rapid increase in warming – was going to come due.
Morton provides examples from other climate scientists, such as Michael Mann, who do not believe Hansen and Co are correct on aerosols or that the 1.5 C threshold has been reached. Other scientists believe he is being too conservative. No one is saying there is no acceleration in global heating; no one serious anyway.
boatsie covers the James Hansen subject in Kitchen Table Kibitzing: “Change your diet, save the climate – eat the rich”
For further reading, from Meteor Blades.
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