A 2023 global heat spike was partly due to reduced sulfate emissions from shipping, which decreased cloud cover and raised temperatures by 0.08°C. Cornell researchers stress the need for stronger emissions cuts and potential climate interventions to manage global warming.
In the summer of 2023, global temperatures rose unexpectedly, surpassing predictions despite the ongoing trend of greenhouse gas-driven warming. Many scientists were puzzled. 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 at Cornell University. “People were saying, ‘Climate change is suddenly accelerating.’ We’d never seen something like this.”
Visioni’s paper, published in Earth System Dynamics, gets to the bottom of it.
Researchers found that mandated reductions in sulfate emissions from international shipping routes in 2020 partly contributed to record-high temperatures. Fewer aerosol particles in the atmosphere lead to reduced cloud cover, weakening clouds’ ability to reflect solar radiation back into space. The study suggests that future policy decisions on rapid reductions in tropospheric aerosols should consider their impact on surface temperatures.
Modeling the Impact of Sulfate Reductions
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.
These changes in the shipping industry had been discussed for years, Visioni said, with the International Maritime Organization (IMO) making a decision in 2014 to begin enforcing stricter sulfate emissions by 2020. Fuels with lower sulfur are much more expensive, so it took some time for the industry to adjust, he said.
The regulation required ships to use fuel with a sulfur content of no more than 0.5%, down from the previous limit of 3.5%. This reduction led to a more than 80% decrease in total sulfur oxide emissions from shipping.
And while there was some talk of this tradeoff within the shipping industry, he said, there was little attempt to call widespread attention to the potential effect.
“There was no attempt to say we should have all eyes on the shipping corridor,” Visioni said. “In hindsight, it would have been great to study that four years ago before the problem manifested itself.”
Quantifying the Temperature Increase
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 increased the planet’s temperature by 0.08 degrees Celsius.
“The unprecedented heat became a normal warm year once you accounted for that,” Visioni said.
Quantifying how much these polluting aerosols reflect heat back into space to make a noticeable increase in the Earth’s temperature is not, Visioni said, a suggestion that these pollution-cutting efforts should be curtailed.
“Air quality improvement is immediate, and everyone is always going to go for that. A lesson here is we make decisions about trade-offs all the time,” he said. “We are reducing air pollution more than was predicted 10 years ago, so there needs to be a lot more open discussion. It means the urgency of emission reduction is even greater.”
The shipping industry has, like many industries, shifted toward alternative fuels to meet the IMO’s decarbonization goals, and methanol, hydrogen, ammonia, wind-assisted propulsion systems, and other technologies are gaining traction.
“We need to be more forceful about emissions reductions,” Visioni said. “We have to bridge a gap. But we should work to prevent warming of the planet through other means. Cloud brightening, geoengineering climate interventions – these are not things that are going to reduce emissions, but they are things we might need to prevent further warming.”
Reference: “Modeling 2020 regulatory changes in international shipping emissions helps explain anomalous 2023 warming” by Ilaria Quaglia and Daniele Visioni, 28 November 2024, Earth System Dynamics.
DOI: 10.5194/esd-15-1527-2024
The study was funded by the Cornell Atkinson Center for Sustainability with a 2030 Fast Grant.
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12 Comments
Interesting
Nice to know what’s going on
James Hansen has been proven correct. He describes it as the devil’s bargain. We are at a point where reducing sulfur pollution for the purpose of saving millions of lives may also cost millions of lives. This also has dire implications for the Earth’s sensitivity to a doubling of carbon dioxide. The presumption is currently about three degrees c but Hanson calculates four and a half.
Nice to know what’s going on keep me up dated
They solved nothing…we SCRUB thru the particles in space and WAY out in the thermosphere its 3000 deg…its all about expansion from burning and SCRUBBIBG…there is no solution now.
This is odd. Climatologists claim clouds are a net increaser to global warming, because it insulates the dark side while reflecting the Sun on the bright side. Supposed to be a net heater.
This is the second time Ive read an article on it being a net cooler. Last time I saw was in 2003 or so.
No, its not bonkers at all. Sadly, what we are experiencing is the evolution of permanent global climate change. We have passed the point of no return. For 40 years we have chosen to listen to the polluters and
do nothing so at this late date it is now too late to correct. We chose $$ over saving our planet. Now we
have to pay the price. From here on we will see hotter blistering hot summers & more wicked winter weather. So long earth. It was nice to have knowed ya.
!
LOL…the earth will be fine. You are certifiably insane
Please do your part by staying off the internet.
In the mid-20th century, reduced atmospheric particulates also raised the global temperature. There is a lesson here, which nobody seems to want to hear.
This is not exactly new info. This happened on 911, when the US grounded all planes for a few days.
There was a theory call Global Dimming, which suggested that smog particles were reducing sunlight to earth. There was actually a request to test the theory, for some large country to ground their airplanes for a day so they could measure whether the temperature would rise or not. They were laughed at, of course. But then 911 happened, and so they got exactly what they needed to test their theory. I believe they measured something like a 1 degree rise in temperature over those few days.
I know it seems odd they could measure that accurately, but they look at the difference between the high and low for the day, rather than just one temp. And somehow they can measure that difference.
I assume something similar happened in the pandemic, when so many cars weren’t commuting to work.
The really bonkers think here is that all our efforts to reduce CO2 emissions by reducing the use of fossil fuels, actually also reduces the smog particles, which seems like it will offset the benefits of CO2 reduction. And the effect of reducing smog particles is almost immediate, but the effects of reducing CO2 takes years, as I understand it.
Just don’t understand why no one seems to be talking about this…
“They found that removing sulfur dioxide from shipping fuel LIKELY increased the planet’s temperature by 0.08 degrees Celsius.”
I question whether we can determine the “planet’s temperature” to a precision of +/- 0.005 degrees C. It is probably better to round up to 0.1 degrees C than to claim that we know the temperature to such a high precision. What does “likely” actually mean? What is the numeric value of the probability and margin of error?
Moving on the the issue of accuracy, we don’t actually have a good measure of the ‘average’ temperature of Earth. What we start with is the mid-range ({Tmax-Tmin}/2) of daily temperatures, which tells us nothing about the variance of the actual temperatures. (While modern weather stations can provide us with virtually instantaneous temperatures, the legacy historical data sets are limited by the ubiquitous diurnal high and low temperatures, which are used to calculate mid-range so-called ‘anomalies.’) The mid-range values alone, lose information such as the fact that daily lows (night and Winter) generally appear to be increasing faster than than the daily highs, despite the fact that it seems that alarmists are always warning us that the oceans are “boiling” or that heat waves are becoming more severe and frequent.
https://wattsupwiththat.com/2019/09/06/the-gestalt-of-heat-waves/
What we end up with is the arithmetic mean of the annual mid-range temperatures, or the difference between that and the ‘baseline’ mid-range temperature for some 30-year period in the past, commonly called an anomaly, which is non-stationary data. That is, an index for the change in the mid-range temperatures. This is where we start delving into non-parametric statistics. That is, the fundamental thing we want to know about, the atmospheric temperature at any time, as provided currently, is lacking statistical descriptors such as mean, mode, median, variance, and kurtosis of the actual temperatures. Non-parametric statistics, lacking such descriptors, are a poor tool for prediction, which is of critical interest.
Definitions are important!