Fossil-fuel emissions, considered a key factor in the phenomenon known as global warming, contain two gases, carbon dioxide and sulfur dioxide, that have opposite effects on atmospheric temperatures. Carbon dioxide traps heat, tending to warm the atmosphere, whereas sulfur dioxide turns into sulfate aerosols that reflect sunlight back toward space, thereby tending to cool the atmosphere. Given that the heat-trapping effect is stronger than the cooling effect, cutting fossil-fuel emissions might be expected to slow the rise in global temperatures. Yet, surprisingly, if fossil-fuel emissions were cut today, global warming would actually be enhanced for more than three decades before the temperature rise began to slow. Which one of the following, if true, most helps to explain the claim made in the last sentence above? ['Carbon dioxide is produced not only by automobiles but also by power plants that burn fossil fuels.', 'Sulfur pollution is not spread evenly around the globe but is concentrated in the Northern Hemisphere, where there is a relatively high concentration of industry.', 'Carbon dioxide stays in the atmosphere for many decades, while the sulfate aerosols fall out within days.', 'Because fossil-fuel emissions contain sulfur dioxide, they contribute not only to global warming but also to acid rain.']