The author’s main purpose in writing the article is to warn of______. A. warm weather B. hot weather C. a new ice age D. a new iceberg
Aerosols are collection of small liquid or solid particles dispersed in air or some other medium. The particles are all so tiny that each is composed of only a few hundred atoms. Because of this they can float in the air for a very long time. Perhaps the most commonly experienced aerosol is industrial smog (烟雾) of the kind that plagued London in the 1950s and is an even greater problem in Los Angeles today. These collections of aerosols reflect the Sun’s heat and thereby cause the Earth to cool.
Dr Rasoo1 and Dr Schneider have calculated the exact effect of a dust aerosol layer just above the Earth’s surface in the temperature of the planet. As the layer builds up, the present delicate balance between the amount of heat absorbed from the Sun and the amount radiated from the Earth is disturbed. The aerosol layer not only reflects much of the Sun’s light but also transmits the infrared (红外线) radiation from below. So, while the heat input to surface drops, the loss of heat remains high until the planet cools to a new balanced state.
Within fifty years, if no steps are taken to stop the spread of aerosols in the atmosphere, a cooling of the Earth by as much as 3.5~C seems inevitable. If that lasts for only a few years it would start another ice age, and because the growing ice caps at each pole would themselves reflect much of the Sun’s radiation it would probably continue to develop even if the aerosol layer were destroyed.
The only bright spot in this gloomy forecast lies in the hope expressed by Dr Rasoo1 and Dr Schneider that nuclear powder may replace fossil fuels in time to prevent the aerosol content of atmosphere from becoming critical.