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Scientists concerned about significant long-term effects of global warming discuss a geoengineering proposal to cool the planet.

Scientist 1

Solar Radiation Management (SRM) could reverse global warming by seeding the stratosphere with sulfuric aerosols (SO4), recreating past periods of global cooling caused by volcanic activity. Naturally reflective sulfate aerosols resulting from this seeding would be dispersed by atmospheric winds, forming a layer of fine particles that would reflect about 1% of sunlight back into space. On the basis of computer models, scientists have predicted that SRM would reduce the amount of sunlight entering earth’s atmosphere, thereby reducing global average temperatures.

Atmospheric CO2 levels were around 275 parts per million (ppm) prior to the Industrial Revolution. A level of 350 ppm is the critical threshold beyond which significant global warming occurs; current levels are around 400 ppm. Since CO2 remains in the atmosphere for a very long time, even eliminating all CO2 emissions immediately would leave global temperatures elevated far into the future. Reducing CO2 emissions alone is not enough to preserve our climate; further action is needed. Preliminary research suggests SRM may be a way to stop or even reverse global warming.

Scientist 2

More research needs to be conducted before seriously discussing the injection of sulfate aerosols into the stratosphere. It will do nothing to affect CO2 levels, and unintended consequences of SRM are so severe that that it should not be considered as a possible "solution" to global warming. There is no way to experimentally predict the consequences of manipulating the atmosphere on a worldwide scale, as climate patterns simply cannot be isolated and manipulated on a local scale.

Injecting sulfate particles into the stratosphere would increase acid rain and have a drastic impact on Earth's protective ozone layer. One study concluded that artificial injections of sulfates could destroy between one-fourth and three-fourths of the ozone layer above the Arctic. This could affect a large part of the Northern Hemisphere because of atmospheric circulation patterns.The sulfates would also delay the expected recovery of the ozone hole over the Antarctic by about 30 to 70 years, or until at least the last decade of the century. A healthy ozone layer is critical for life on Earth because it blocks dangerous ultraviolet radiation from the sun.

Adapted from: Rotman, David. A Cheap and Easy Plan to Stop Global Warming. MIT Technology Review. 8 Feb 2013. AND National Science Foundation Press Release 08-069. “Injecting Sulfate Particles into Stratosphere Could Have Drastic Impact on Earth's Ozone Layer.”

Choose the option that best answers the question.

Which of the following statements best explains why Scientist 1 mentioned sulfuric aerosols?