Shipping emissions reduction in 2020 ‘likely’ led to 2023 temperature spike, study finds – so the spike should last?

Thermometer with Fahrenheit and Celsius units [image credit: Stilfehler at Wikipedia]

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Once again climate models are claimed to be able to prove things. These same models have consistently overestimated observed warming by sometimes wide margins. If there’s a spike, it should persist since the shipping emissions reduction is supposed to be permanent. Conversely, if the model isn’t correct the spike could fade away.
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The summer of 2023 saw a surprising increase in global temperatures, even within the context of the ongoing greenhouse gas-driven warming trend, says Phys.org.

Many scientists were flummoxed. Their simulations didn’t show this kind of spike.

“Climate scientists were saying this is essentially impossible, that it is bonkers to see such a jump all at once,” said Daniele Visioni, assistant professor in the Department of Earth and Atmospheric Sciences. “People were saying, ‘Climate change is suddenly accelerating.’ We’d never seen something like this.”

Visioni’s paper, “Modeling 2020 Regulatory Changes in International Shipping Emissions Helps Explain Anomalous 2023 Warming,” published Nov. 28 in Earth System Dynamics, gets to the bottom of it.

Mandated reductions in sulfate emissions from international shipping routes in 2020 are partly responsible for the record high temperatures, the researchers found. Reducing the amount of aerosol particles in the atmosphere reduces cloud coverage; thus, clouds’ ability to reflect solar radiation back to space is diminished.

The paper’s findings suggest future policy decisions around abrupt reductions in tropospheric aerosols should take into account their surface temperature impact.

Past research indicated that such change would lead to a minor increase in the global temperature due to a reduction in cloud formation, but Visioni and co-author Ilaria Quaglia, postdoctoral researcher in the Sibley School of Mechanical and Aerospace Engineering (Cornell Engineering), used Earth system model simulations to prove the significance of the sudden drop in sulfate shipping emissions. [Talkshop comment – models can’t *prove* things]
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The Cornell researchers looked at monthly global temperature anomalies over the period 2020–23, removing the assumed linear contribution from greenhouse gases and seasonality, in order to determine the shipping industry’s impact on temperature anomalies.

They found that removing sulfur dioxide from shipping fuel likely [sic] increased the planet’s temperature by 0.08°C.

“The unprecedented heat became a normal warm year once you accounted for that,” Visioni said.

Full article here.
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Image: Thermometer with Fahrenheit and Celsius units [credit: Stilfehler at Wikipedia]