Weather

[A]s science investigates the natural environment, it also modifies it, and that modification may have incalculable consequences for evil as well as for good...

[S]cience has the power for the first time in history to undertake experiments with premeditation which can irreversibly alter our biological and physical environment on a global scale.  The problem is difficult, because it is hard to know in advance whether the cumulative effects of a particular experiment will help or harm mankind.

--John F. Kennedy, October 22, 1963
Address at the Anniversary Convocation of the National Academy of Sciences.