July 23, 2011

Atmospheric Particles Slow Global Warming: NOAA

Volcanic ash from small-scale eruptions and soot resulting from the burning of fossil fuels may be responsible by slowing the rate of global warming up by to 20-percent, according to the results of a new National Oceanic and Atmospheric Association (NOAA) study released Thursday.

Particles such as these, commonly referred to as "aerosols", can reflect sunlight back into space once they reach the stratosphere, which according to an NOAA press release, "leads to a cooling influence on the ground."

In the study, which has been published in the online edition of the journal Science, the organization determines that an increase in the number of particles in the atmosphere "has offset about a third of the current climate warming influence of carbon dioxide (CO2) change during the past decade."

"Stratospheric aerosol increased surprisingly rapidly in that time, almost doubling during the decade," NOAA Earth System Research Laboratory (ESRL) Physicist and study author John Daniel said in a statement. "The increase in aerosols since 2000 implies a cooling effect of about 0.1 watts per square meter--enough to offset some of the 0.28 watts per square meter warming effect from the carbon dioxide increase during that same period."

The reason for the increase in these stratospheric aerosol particles are unclear at this time, and is the topic on ongoing research, noted study co-author Ryan Neely, a member of the University of Colorado and the Cooperative Institute for Research in Environmental Sciences (CIRES).

However, the NOAA believes that natural sources, including smaller-scale volcanic eruptions, and sulfur-emitting human activity likely played a role in the aerosol spike.

"The findings show that both natural and human factors have slowed the rate of global warming 20 percent since 1998," Juliet Eilperin of the Washington Post wrote in a Thursday article. "The study is significant because although average global temperatures last decade were higher than in the 1990s and 1980s, it appears the rate of warming has slowed compared with previous decades."

The potential implications of this study could potentially lead to an inexpensive but fairly radical solution to global warming, observes BBC News Environmental Correspondent Richard Black.

"The cheapest of all geo-engineering techniques yet conceived involves putting multiple tons of this stuff into the stratosphere, where it would reflect sunlight back into space, cooling the Earth's surface," he wrote in a July 21 column.

"Controversial, of course; but a number of eminent people such as UK renewable energy pioneer Stephen Salter suggest that research should begin in earnest, because they don't believe our society is going to curb greenhouse gas emissions at anything like the rate needed to slow global warming," Black added. "Clearly, if this is ever to be attempted, understanding how the particles will behave in the upper atmosphere would be of paramount importance."

Joining Daniel and Neely as authors of the NOAA study were Susan Solomon of the University of Colorado, J.P. Vernier of the NASA-Langley Research Center and University of Paris, Ellsworth Dutton of the Global Monitoring Division of NOAA-ESRL, and Larry Thomason of NASA-Langley.


Image 1: Lidar instruments - pointing up from the ground or down from satellites - use reflected light to measure the amounts of particles and their locations, which can influence climate. Credit: CIRES/NOAA

Image 2: Sources of aerosols reach the stratosphere from above and below, as shown in the graph. Sulfur dioxide (SO2), carbonyl sulfide (OCS), and dimethyl sulfide(DMS) are the dominant surface emissions which contribute to aerosol formation. Credit: NOAA


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