In a Conversation with Her Friends, Dana Was Asked to Give

Multiple Choice

In a conversation with her friends, Dana was asked to give an example of an environmental tipping point. Which of the following would she offer?

A) Researchers reporting that they had discovered a connection between wind power turbines and hearing loss in humans.
B) Researchers reporting that permafrost in a region of Siberia has started to melt for the first time since it formed 11 000 years ago at the end of the last ice age.
C) Researchers reporting that global warming is responsible for the increase of methane in the atmosphere.
D) Researchers reporting an increasing number of community gardens in urban areas.