The Greenhouse Effect Is a Natural Phenomenon That Keeps the Earth's

The greenhouse effect is a natural phenomenon that keeps the earth's surface warm. Without greenhouse gases-water vapor, carbon dioxide, methane, nitrous oxide, halocarbons, and ozone-life as we know it wouldn't exist. The current problem is that

A) there are more cooling than warming radiative forcings.
B) the atmospheric concentration of greenhouse gases has reached its highest level in 400,000 years, and this rise has upset the balance of radiative forcings working to warm and cool the earth.
C) scientists cannot agree on a general model of how the greenhouse effect went from being a positive to a negative and a life-threatening force.
D) global warming actually benefits 90 percent of the world population, so it is difficult to mobilize the will to address the anthropogenic causes of climate change.
E) it is difficult to distinguish between climate change and global warming.