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April 28, 2009
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Aerosols may drive much Arctic warming, scientists find
April 9, 2009
Courtesy NASA
and World Science staff
Discussions on global warming usually center on
the heat-trapping greenhouse gases blamed for the trend. But new NASA research suggests around half the atmospheric warming measured in the Arctic is due to airborne particles called aerosols. Aerosols can influence climate directly by either reflecting or absorbing the sun's radiation as it moves through the atmosphere. The tiny airborne particles enter the atmosphere from sources such as industrial pollution, volcanoes and residential cooking stoves.
(Image courtesy NASA Goddard Scientific Visualization Studio)
Emitted by natural and human sources, aerosols can influence climate by reflecting or absorbing sunlight. The particles also affect climate less directly by changing cloud properties, such as reflectivity. For one type of aerosol, scientists said, reductions rather than increases in its emissions seem to have promoted warming.
A study led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies in New York used a computer model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols.
The investigators found that Earth’s middle and high latitudes are especially responsive to changes in aerosol levels. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming
measured in the Arctic since 1976. The results are published in the April issue of the research journal
Nature Geoscience.
Though there are several types of aerosols, previous research indicates two — sulfates and black carbon — play leading roles in climate. Both are products of human activity. Sulfates, which come mainly from the burning of coal and oil, scatter sunlight and cool the air. Over the past three decades, the United States and European countries have passed
clean-air laws that have halved sulfate emissions, researchers said.
The models showed that regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976, in particular the Arctic, Shindell said; in the Antarctic, aerosols play less of a role.
Researchers with the U.S. National Oceanic and Atmospheric Administration
reported in the April 3 issue of the journal Geophysical Research
Letters that Arctic summers may be ice-free in as few as 30
years. That was the latest in a series of increasingly nearer-term
forecasts for Arctic melting from various scientific groups.
The Arctic region has seen its surface air temperatures rise by 1.5 C (2.7 F) since the mid-1970s. In the Antarctic, surface air temperature has increased about 0.35 C (0.6 F). That makes sense, Shindell explained, because the Arctic is near North America and Europe, highly industrialized zones that produce most of the world’s aerosols.
“In the mid-latitudes of the Northern Hemisphere and in the Arctic, the impact of aerosols is just as strong as that of the greenhouse gases,” said Shindell. “If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we’re much better off looking at aerosols and ozone” than the greenhouse gas carbon dioxide whose emissions many environmentalists
are targeting, he added.
Aerosols tend to be short lived, staying in the atmosphere for just days or weeks, whereas greenhouses gases can persist for centuries. Atmospheric chemists thus think the climate may respond most quickly to changes in aerosol levels.
NASA’s upcoming Glory satellite is designed to enhance current aerosol measurement capabilities to help scientists reduce uncertainties about aerosols by measuring the distribution and properties of the particles.
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Discussions on global warming usually center on heat-trapping greenhouse gases blamed for the trend. But new NASA research suggests around half the atmospheric warming measured in the Arctic is due to airborne particles called aerosols. Emitted by natural and human sources, aerosols can influence climate by reflecting or absorbing sunlight. The particles also affect climate less directly by changing cloud properties, such as reflectivity. For one type of aerosol, scientists said, reductions rather than increases in its emissions seem to have promoted warming. A study led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies in New York used a computer model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols. The investigators found that Earth’s middle and high latitudes are especially responsive to changes in aerosol levels. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades. The results are published in the April issue of the research journal Nature Geoscience. Though there are several types of aerosols, previous research indicates two — sulfates and black carbon — play leading roles in climate. Both are products of human activity. Sulfates, which come mainly from the burning of coal and oil, scatter sunlight and cool the air. Over the past three decades, the United States and European countries have passed laws that have halved sulfate emissions, researchers said. The models showed that regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976, in particular the Arctic, Shindell said; in the Antarctic, aerosols play less of a role. The Arctic region has seen its surface air temperatures rise by 1.5 C (2.7 F) since the mid-1970s. In the Antarctic, surface air temperature has increased about 0.35 C (0.6 F). That makes sense, Shindell explained, because the Arctic is near North America and Europe, highly industrialized zones that produce most of the world’s aerosols. “In the mid-latitudes of the Northern Hemisphere and in the Arctic, the impact of aerosols is just as strong as that of the greenhouse gases,” said Shindell. “If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we’re much better off looking at aerosols and ozone” than the greenhouse gas carbon dioxide whose emissions are targeted by many environmentalists, he added. Aerosols tend to be short lived, staying in the atmosphere for just days or weeks, whereas greenhouses gases can persist for centuries. Atmospheric chemists thus think the climate may respond most quickly to changes in aerosol levels. NASA’s upcoming Glory satellite is designed to enhance our current aerosol measurement capabilities to help scientists reduce uncertainties about aerosols by measuring the distribution and microphysical properties of the particles.