In last week's story about Environmental Defense ("The Devil's Advocate," September 24), James Verini described our work to build voluntary coalitions that achieve real environmental results -- from protecting the oceans to reducing pollution. But the article may have left a misimpression on a key point of our global warming policy: There is no substitute for government action. Only a cap on greenhouse gas pollution will create the market incentives necessary to fix this problem -- because only a cap will create a monetary value for reduced emissions and drive investment into new energy technologies. Voluntary coalitions like the US Climate Action Partnership -- which was formed by the joint efforts of several environmental and corporate leaders -- are a means to achieve that government action, not a substitute for it.

As an organization founded by scientists, we judge any proposal by its ability to deliver results for the environment. By that measure, a mandatory cap on greenhouse gas pollution -- like the one adopted by much of the industrialized world and an increasing number of US states, from California to New Jersey -- is the indispensable element of effective energy and climate policy. It's time for Congress to deliver it.

Fred Krupp
President, Environmental Defense