Curbing sulfur
It turned out that there was a huge spike in sulfur emissions up until the 1980s, at which point sulfur pollutants dropped, Wild said. The drop in sulfur emissions corresponds with the introduction of legislation in a number of countries to reduce air pollution, Wild said. (Diesel exhaustoften contains high levels of sulfur compounds.)
It's not surprising to scientists that higher levels of pollutants could dim the Earth's surface: After volcanic eruptions, for instance, the huge amounts of sulfur spewed into the atmosphere can cool the planet for a few years. That's because the tiny particles can scatter and absorb light, reducing how much of that light ultimately reaches the Earth's surface, Wild said.
Air pollution can also alter the light reaching Earth in other ways.
"Polluted clouds, counterintuitively, become brighter," Wild said. "The polluted clouds can also stay longer in the air because their droplets are small." [In Images: Mysterious Night-Shining Clouds]
Here's how the cloud brightening works: Aerosols that are normally in the air are insoluble and act as seeds for water droplets to condense around, and ultimately to form clouds. Polluted air, on the other hand, contains water-soluble particles, leading to clouds with more, yet smaller, water droplets. These numerous and tiny droplets provide more surfaces for light to reflect off, and voilà — brighter clouds.
These brighter clouds also reduce how much light reaches the ground, he added.
What's more, this unintentional geoengineering may have already impacted global warming, Wild said. Global temperatures held fairly constant from the 1950s to the 1980s, and warming only accelerated starting in 1985, when the global brightening seems to have begun, Wild reported in a study published this month in the journal WIREs Climate Change.
He also sees evidence that this unintentional geoengineering affected the world's hemispheres differently. Temperatures held steady until the mid-1980s in the Northern Hemisphere, where most of the world's population lives, and spiked up sharply afterward. By contrast, in the "relatively more pristine" Southern Hemisphere, which has much fewer people, the region experienced a steadier uptick in warming. That suggests that air pollution had a measurable effect on global warming on the globe's northern half, and less so in the southern half, he said.
Curbing sulfurIt turned out that there was a huge spike in sulfur emissions up until the 1980s, at which point sulfur pollutants dropped, Wild said. The drop in sulfur emissions corresponds with the introduction of legislation in a number of countries to reduce air pollution, Wild said. (Diesel exhaustoften contains high levels of sulfur compounds.)It's not surprising to scientists that higher levels of pollutants could dim the Earth's surface: After volcanic eruptions, for instance, the huge amounts of sulfur spewed into the atmosphere can cool the planet for a few years. That's because the tiny particles can scatter and absorb light, reducing how much of that light ultimately reaches the Earth's surface, Wild said.Air pollution can also alter the light reaching Earth in other ways."Polluted clouds, counterintuitively, become brighter," Wild said. "The polluted clouds can also stay longer in the air because their droplets are small." [In Images: Mysterious Night-Shining Clouds]Here's how the cloud brightening works: Aerosols that are normally in the air are insoluble and act as seeds for water droplets to condense around, and ultimately to form clouds. Polluted air, on the other hand, contains water-soluble particles, leading to clouds with more, yet smaller, water droplets. These numerous and tiny droplets provide more surfaces for light to reflect off, and voilà — brighter clouds.These brighter clouds also reduce how much light reaches the ground, he added.What's more, this unintentional geoengineering may have already impacted global warming, Wild said. Global temperatures held fairly constant from the 1950s to the 1980s, and warming only accelerated starting in 1985, when the global brightening seems to have begun, Wild reported in a study published this month in the journal WIREs Climate Change.He also sees evidence that this unintentional geoengineering affected the world's hemispheres differently. Temperatures held steady until the mid-1980s in the Northern Hemisphere, where most of the world's population lives, and spiked up sharply afterward. By contrast, in the "relatively more pristine" Southern Hemisphere, which has much fewer people, the region experienced a steadier uptick in warming. That suggests that air pollution had a measurable effect on global warming on the globe's northern half, and less so in the southern half, he said.
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