Which of the following is not a theory supporting global warming? a. It is predicted that the average temperature will rise 1.4° C or more over the next 100 years. b. Human activity has increased greenhouse gases. c. Over the last 100 years the earth has warmed by 0.74° C d. Carbon dioxide is an insignificant greenhouse gas.

The answer is D. Carbon dioxide is an insignificant greenhouse gas. Carbon dioxide is actually a significant greenhouse gas and contributes greatly to the global warming seen on Earth. One example is seen on the hottest planet in the Solar System, Venus. 96.5% of Venus's atmosphere is Carbon dioxide, heating the planet to a balmy 872 degrees Fahrenheit from the greenhouse effect of that gas.