Preparing for the 21st Century: Challenges Facing A Changing Society http://www.nas.edu/21st/environment/ Environmental awareness among the public and policymakers has been growing since the 1960s, when it became widely recognized that human activities were having harmful and large-scale effects on the environment.
(http://www.nas.edu/21st/environment/; has been growing; T:since the 1960s)
http://www.nas.edu/21st/environment/
has been growing
T:since the 1960s