The aerosols conundrum
Just how much warmer Earth will become as a result of greenhouse-gas emissions — and how much it has warmed since preindustrial times — is much debated. In a 2007 report, the Intergovernmental Panel on Climate Change, an agency formed by the world’s largest governments to assess climate change, said that the planet’s average surface temperature will rise by between 2 and 11.5 degrees Fahrenheit by 2100, with a best estimate at between 3.2 to 7.2 degrees F. However, the IPCC’s computer models have a record of overestimating warming: If the IPCC models were right, the planet should now be hotter than it is. The IPCC attributes the discrepancy to aerosols — microscopic particles in the atmosphere that are created by both nature (dust blown by desert winds) and human activity (liquid droplets created from fuel combustion). Because aerosols help cloud droplets form into icy particles and reflect sunlight back...