However, burning fossil fuels not only causes global warming, but also coolingAir pollution, which has claimed tens of millions of lives, is one of the great ironies of climate change. Some of the worst effects of global warming.
The fine particles produced by burning coal, oil, and gas reflect sunlight and encourage the formation of clouds that block the Earth’s sunlight. Since the 1980s, these particles have 40 percent and 80 percent Global warming caused by greenhouse gases.
And now, as society cleans up, that cooling effect is fading: New regulations have reduced the amount of sulfur aerosols emitted from global shipping traffic across the oceans, and China has dramatically reduced its sulfur pollution over the past decade as it battles its own air pollution problem.
The result will be further increases in temperatures, although exactly how much is still a matter of debate. The answer will have lasting implications for humanity’s ability to meet climate goals.
“We’re starting out in a very uncertain zone,” said Zeke Hausfather, a climate scientist at payments company Stripe and lead researcher. “It’s possible that the temperature drop is completely hidden.”
Most of the cooling effect of air pollution comes from sulfur aerosols, which act in two ways: the particles themselves are reflective and bounce the sun’s rays back, blanketing the planet, and they also make existing clouds brighter and more mirror-like, cooling the planet.
Coal and oil 1 to 2 percent sulfur — And when humans burn fossil fuels, they release that sulfur into the atmosphere. This is deadly: Sulfur dioxide has been linked to respiratory problems and other chronic diseases, and air pollution is responsible for about 1 in 10 deaths worldwide.
Over the past few decades, countries have been working to phase out these pollutants, beginning with the United States and the European Union, followed by China and India. China has reduced its sulfur dioxide emissions by more than 70% since 2005 by installing new technology and scrubbers in fossil fuel plants. More recently, the International Maritime Organization set a limit on the amount of sulfur that can be in marine fuels in 2020. — One of the most polluting fuels used in shipping, sulfur dioxide emissions from ships fell immediately by about 80%. Mediterranean countries Similar transport regulations Towards 2025.
“We’ve seen a pretty steep decline over the last decade,” said Duncan Watson-Paris, an assistant professor at the Scripps Institution of Oceanography at the University of California, San Diego.
These measures have saved an estimated 200,000 premature babies. Several deaths have already been averted in China and the new shipping regulations could save around 50,000 lives a year. Global temperatures. Scientists estimate that aerosol changes due to the new shipping regulations alone could lead to 0.05 to 0.2 degrees Celsius of warming over the next few decades.
Some researchers The findings suggest that changes in maritime shipping regulations may have been a major factor in last year’s record heat, and that aerosols may have been hiding much more heat than previously thought. rejection After sulfur emissions were reduced.
“NASA satellite data shows that in the areas where this would occur, there is a very large increase in absorbed solar radiation,” said Leon Simmons, an independent researcher and member of the Club of Rome in the Netherlands, pointing to the shipping areas that would be affected by the new rules. “And we see an increase in sea surface temperatures in the same areas during this time.”
new paperScientists from the University of Maryland have argued that the decline in aerosols could cause global warming to double in the 2020s compared to the rate since 1980. But other researchers Criticized Their results.
Most experts consider the impact to be modest, between 0.05 and 0.1 degrees Celsius. “In terms of uncertainty, I think it’s unlikely we’ll see a doubling or more,” said Michael Diamond, a professor of meteorology and environmental science at Florida State University.
Some scientists see the boat ban as similar to a less-polluting way researchers are exploring to intentionally brighten clouds to stop global warming. In Alameda, California, researchers recently took a first step by releasing sea-salt aerosols into the atmosphere to study how the particles brighten clouds and reflect sunlight. City officials later halted the project, despite reports that the experiment was safe.
But the real problem is yet to come. Currently, the UN’s Intergovernmental Panel on Climate Change estimates that aerosols are hiding about 0.5 degrees of global warming. But that figure could be as much as 1 degree higher or as little as 0.2 degrees lower. That difference could be the difference between meeting the 2015 target or not. Paris Agreement or not?
For example, if aerosols were masking more cooling than expected, the world could unknowingly overshoot its climate targets by a large margin.
Under the Paris Agreement, nearly 200 countries around the world committed to keeping global warming to well below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. Scientists believe that a warming between 1.5 and 2 degrees would cause many dangerous impacts, from the collapse of coral reefs to the melting of major ice sheets.
“This isn’t just about greenhouse gas emissions,” said Robert Wood, a professor of atmospheric sciences at the University of Washington. “Cleaning up quickly or continuing to fumble with the same aerosol emissions could be the difference between crossing the 2°C threshold or not.”
No scientist would argue for an end to aerosol removal efforts because air pollution causes so many deaths. “There are good reasons to want to remove air pollution,” Diamond says. “The public health benefits are really important.”
But researchers worry that removing air pollution without stopping fossil fuel use, as China is doing, for example, could lead to even greater and more rapid warming. “You have to make sure you’re doing it at the same time as removing methane and carbon dioxide,” Diamond said. Reducing methane emissions could help offset the effects of reduced aerosols, he noted. Methane has a warming effect, but like aerosols, it doesn’t stay in the atmosphere for long.
Still, many scientific questions remain, and until those are answered, the world won’t know exactly how much warming is evident from falling aerosols.
Harry Stevens contributed to this report.