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In an Odd Twist, Cleaner Air in China May Mean a Warmer Earth

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Over the past 15 years, Chinese officials saved the lives of an estimated more than 200,000 residents by reducing the air pollution from coal-fired power plants. But this public health campaign has an unfortunate side effect: The drop in pollutants is helping warm the planet.

In fact, China’s push to continue cleaning up its air in the future could warm the entire northern hemisphere by 0.1 degrees Celsius by the end of the century, making it even tougher to keep the Earth’s temperature below the 1.5 Celsius degree (2.7 degrees Fahrenheit) warming limit that scientists say is necessary to avoid severe weather disruptions, increased rainfall, sea level rise, droughts, and other disastrous climate change effects by the year 2100. That’s because the same sulfur dioxide particles that come from coal burning and cause respiratory problems in humans also reflect sunlight, which cools the planet.

In a new study published this week in the journal Environmental Research Letters, a team of researchers from China and the United States analyzed emissions data between 2006 and 2017 during China’s big air cleanup. By installing scrubbers and other new technologies on older coal plants and other factories, the country cut sulfur dioxide emissions by 70 percent. The researchers then developed a computer model to forecast how this change in air quality would affect something called “radiative forcing,” or the amount of the sun’s energy that becomes trapped by the Earth’s atmosphere, minus the energy the Earth reflects back to space.

The scientists ran their model to simulate the passage of 150 years at both the higher 2006 emissions rate and the lower 2017 emissions rate. Then they looked at what the temperature changes would be after about a century. The results show that the emissions reductions will allow more energy to reach the