May 6, 2013
Pollutants Effect On Clouds Could Actually Lead To Climate Cooling
redOrbit Staff & Wire Reports - Your Universe Online
While manmade pollution and other natural emissions are often blamed for their role in global warming, new research from the University of Manchester suggests that they could actually play a role in cooling the world´s climate.
According to the study, which has been published in the journal Nature Geoscience, those emissions could make clouds brighter. Clouds, the researchers explain, are comprised of water droplets that condense onto minute particles suspended in the air. Those particles swell into cloud droplets when the air reaches a high enough level of humidity.
Scientists have long known that the number and size of those particles affect how bright clouds appear to be from the top. That, in turn, impacts how effective clouds are at scattering sunlight back into space. Climate experts have struggled to understand exactly what impact this phenomenon has on global warming, especially in parts of the world where there tends to be large amounts of pollution or natural emissions.
These particles can be the result of sea spray or dust, or they could originate from automobile exhaust fumes or industrial activities, the researchers explained. They typically contain a sizable amount of organic matter and tend to be volatile in nature, existing as a vapor in warm conditions.
During their study, the authors discovered that this effect is reversed in the atmosphere, as the volatile organic compounds evaporate and let off aromas. However, under the moist, cool conditions under which clouds form, these molecules prefer to be in the liquid state and create larger particles that are more effective seeds for cloud droplets.
“We discovered that organic compounds such as those formed from forest emissions or from vehicle exhaust, affect the number of droplets in a cloud and hence its brightness, so affecting climate,” said study author Professor Gordon McFiggans of the University of Manchester's School of Earth, Atmospheric and Environmental Sciences.
“We developed a model and made predictions of a substantially enhanced number of cloud droplets from an atmospherically reasonable amount of organic gases,” he added. “More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds.”