A、Significantly increasing the temperature of the Earth. B、Significantly cooling the Earth. C、Keeping the atmosphere reasonably

Climate researchers still do not agree on whether the earth will become warmer during the century. Even more importantly, none of them expect the planet to get very much warmer in the foreseeable future. They say that the earth is likely to warm by no more than 2 degrees Centigrade during this century.
     Satellite studies indicated that additional cloud cover would moderate any warming trend. Highly ac curate satellite data for the last nineteen years show a slight cooling of the atmosphere. Most of the one-half-degree Centigrade of warming that has occurred in the last one-hundred years took place before 1940—before humanity put very much CO2 into the air. Thus there is strong evidence that the two are unconnected.
    Research has only recently produced a computerized climate model able accurately to mimic the weather the world has accurately had. This more-accurate model projects only a 2-degree Centigrade increase in temperatures.
    Between 900 AD and 1300 AD, the earth warmed by some 4 to 7 degrees Fahreheit—almost exactly what the models now predict for this century. History books call it the Little Climate Optimum. Written and oral history tells us that the warming created one of the most favorable periods in human history, crops were plentiful, death rates diminished, and trade and industry expanded—while art and architecture flourished,
    Researchers tell us that we need not fear a return of the Little Climate Optimum. If there is any global warming in the 21th century, it will produce milder weather that marked the medieval Little Optimum—with the added benefit of more CO2 in the atmosphere and therefore a more luxuriant natural environment.