Your Friend Is Wary of Environmentalists' Claims That Global Warming

Your friend is wary of environmentalists' claims that global warming could lead to major biological change on Earth. Which of the following statements can you use in response to your friend's suspicions?

A) We know that atmospheric carbon dioxide has decreased over the past 150 years.
B) Through measurements and observations, we know that carbon dioxide levels and temperature fluctuations are indirectly correlated.
C) Global warming could have minor effects on agriculture in the United States.
D) Scientist have evidence that climate change has already altered primary production, as well as ecosystem services.