COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	\input jmclet
C00005 ENDMK
C⊗;
\input jmclet
\jmclet
\vskip 10pt
\address 
Editorial Correspondence
Science
1333 H Street NW
Washington, D.C. 20005

\body
To the Editor:

	It seems that the heat balance of the earth is substantially
affected by relatively small amounts of various compounds in the upper
atmosphere. Much research, e.g. (1), describes effects of emissions
that are by-products of human activity aimed at other purposes.

	There needs to be research aimed at discovering how to use
this phenomenon to humanity's advantage.  The most obvious objective is to
be able to avert ice ages and little ice ages and perhaps even to cancel
the climatic effects of large volcanic eruptions.

	More generally, it seems unlikely that Nature is so benevolent
that the present heat balance is optimal.  Moreover, differential effects
may be possible, i.e. to make different changes in different places.
Perhaps more places can have a California climate.

	Even taking the usual gloomy environmentalist viewpoint in which
all change is bad, it may turn out that the best way to avoid undesirable
changes presently projected, is to emit substances into the upper
atmosphere that will counter the effects of the substances being
inadvertently admitted.

	Understanding aimed at control should be our goal.


\centerline{REFERENCE}

\noindent 1. V. Ramanathan, {\it Science}, {\bf 240}, 293 (1988).

\closing
Sincerely,

John McCarthy
Computer Science Department
Stanford University
Stanford, CA 94305

\end