New York: A team of researchers has uncovered the processes behind the formation and evolution of small atmospheric particles free from the influence of pollution that can help them create accurate models to predict global climate change. Clouds and aerosols -- small airborne particles that can become the seeds upon which clouds form -- are essential to climate predictions because they reflect sunlight back into space, according to the researchers, including scientists from the Carnegie Mellon University in the US. Reflecting light away from Earth can have a cooling effect, masking some of the warming caused by greenhouse gases. "The best estimate is that about one-third of the warming by greenhouse gas emissions is masked by this aerosol cooling, but the fraction could be as large as half and as little as almost nothing," said Neil Donahue from Carnegie. In order to have complete climate prediction models, scientists need to incorporate clouds and aerosols into their calculations, but understanding how new aerosol particles form and grow in the atmosphere, and how they affect clouds and climate, has been challenging. The new study, published in the journal Nature, found that new particles can form exclusively from the oxidation of molecules emitted by trees without the presence of sulfuric acid. Sulfuric acid largely arises from fossil fuels, so the new findings provide a mechanism by which nature produces particles without pollution. "This softens the idea that there may be many more particles in the atmosphere today due to pollution than there were in 1750, and suggests that the pristine pre-industrial climate may have had whiter clouds than presently thought," Donahue said.