Read the text below then answer the following questions.

What is Global warming?

    Global warming is a term used to describe a gradual increase in the earth's average ground and atmospheric temperatures across the whole planet. Measurements indicate that the global temperature has increased by about 1 degree Fahrenheit in the past century. This warming trend appeared during a period when human activities were beginning to increase the carbon dioxide (CO2) and other greenhouse gases in the atmosphere.

    Although most scientists believe that a rise in carbon dioxide emissions will lead to further global warming, uncertainties remain about the timing and severity of resulting climatic change.

    Neverthesless, many are convinced that human activities are partly responsible for the long-term warming, of the fast century and that climatic changes caused by greenhouse gas increases will be continuing part of our future.

    The impact of global warming could be devastating. Global warming cause ozone depletion, melting polar ice, and rising ocean levels. The ozone layer, which protect all life from ultraviolet (UV) radiation, is being destroyed by the realese of chlorofluarcocarbons (CFCS) into the atmosphere. The widening holes in the ozone layer allow in more UV rays, which can cause skin cancers, cataracts, and immune system damage. UV rays are detrimental to pollination, seed production, and marine life food supplies as well.

    Ice sheets in the Artic Ocean have receded to record lows, and Antarctic glaciers are melting at fast rate, causing sea levels to rise and indigenous wildlife to lose its habitat. Rising ocean levels could eventually cause worldwide flooding of coastal areas, forcing people and wildlife to migrate inland. Many expert predict global warming will cause a dramatic increase in excessive rainfall in some areas and severe drought in other, resulting in floods, crop failures, and a rising number of forest fires and land slides

    Many of the world's most knowledgeable climate-change scientist forecast that the earth's temperature will rise from 1.44 to 6.3 F by the year 2100 if we don't take steps to reduce greenhouse gases. An increase of 1 to 3.6 F will occur event if we do act, because many gases have already been released.

What do the climate-change scientists forecast if we don't take steps to reduce greenhouse gases?