According to the U.S. Environmental Protection Agency,

Chapter 2, Problem 24

(choose chapter or problem)

According to the U.S. Environmental Protection Agency, carbon dioxide makes up 84.6% of the total U.S. greenhouse gas emissions. Carbon dioxide, or \(\mathrm{CO}_{2}\), arises from the combustion of coal, oil, and gas. Greenhouse gases trap heat on our planet, causing it to become warmer. Effects of this phenomenon are already being seen in increased melting of glaciers and permafrost. If this continues unchecked, water levels will rise, causing flooding in coastal communities, where the majority of the U.S. population lives. (See Exercise 13.) The graph at the top of the next page shows the average rate of change in the concentration of atmospheric \(\mathrm{CO}_{2}\) since 1990. (Note that before 1900 the average rate of change in \(\mathrm{CO}_{2}\) emissions was typically 0.2 ppm or below.)

a. Is the average rate of change always positive? If so, does that imply that the amount of atmospheric carbon dioxide is always increasing? Explain your answer.

b. What does it mean when the average rate of change was decreasing (though not negative)?